shell - well planning

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. - ~ ' \ , L W . ~ t d ~SHORT NOTES. C/--T;t, ~

~ 3~ " " - ~ - - - -

WELL PLANNING

AND

PROPOSAL FOR

PRODUCTION GEOLOGISTS

IN THE

PETROLEUM INDUSTRY

P.O.Okeke



1\11 Ilgllls reserved. No part of this publication

111ily 1)(' reproduced. stored in ' a retrievalsyl'l ( ' I I I or l ransmit led in any form or by any

11H'r1llh. eleclronic. me.cl18nica l. photocopying, 9n'('C)J(\Il1i!, or otherWise wlthoul the pnor

pernJiI'lHIOl1 of' the Publisher.

I-F ',

1\

FII : ' ( Publi.shed 2006

DulllCS Publishing Co. Ltd.

J \/'!.7 ('111111(' Avenue, New I-Iaven. Enugu.

'1\'1: 011·2 310903, 0803-955-5253

(0 P.O. Okeke, 2006

ISI3N 978-32:327 - 1-1

CONDITIONS OF SALES

Published and Printed in Ni/4eria by

Dulacs Publishing an d Printing Press Ltd.

ii

~

J

PREFACE

The ability of the geologists in handling

seismic and well log data will either lead

positively or mislead later well 'jJlanners

(geophysicists, petrophysicists and reservoir

engineers) and drillers. This is th e bottomline. Everything must be done in o rder to dril la successful well. Nobody would like to be

heJd responsiblc for any failure. The entir e

approach must be interactive.

What you will read in this text book ar e

short notes that could enable a potential

production geologist contribute meaningfully

so that a good result is achieved. Petroleumexploitation and development remain a very

expensive bus iness, and mistakes must be

reduced as much as humanly possible.The book is divided into five chapters:-

(i) Chapier I - Usefulness of production

Geology in Well Planning and

Proposal,

(ii) Chapter 2 - Log Correlation

techniques. Deviated/Directionally

drilled wells and Mul1Jlaterals,(iii) Chapter 3 - Well Log Evaluation.

(iv) Chapter 4 - Well Planning and

Proposal (A Summary), and

ii i

"



CONTENTS Mature ~ i t ~ l d e.g NigerDelta.'.Ni.geria': 'I : :.... i, ' 8Oil in Agbada Formation . . ,

(Niger Delta. Nip:eria) .. 8True Verlical Thickness

(TVT)I) f

Expected Grq§E! sandThiclcness., .. ft·· 8. Deviation Data . } . . ! J ~ .. -.,,:: 11

Q r q ~ $ - s e c t i Q n S n , . . .. 12

l ) a t a r e q l l i t e ~ f ' Q ~ W : e l 1 , P l ~ n ~ ~and ProPQsa] '" , __« •• 15

G e o p h y ~ i c a i p i . : o ~ p e ; C t i n g in 'the search, for Petroleum

,Aswmmaxy. . . . . 16 :

Ba.siC Materials needed in the ...

detennination of the b Y d r o c a . r b ~ , ~ ·potentiql Qf ClJly ,reservoir level

q ~ Q Q ~ _ . .",': ",. .. 24

: ~ d r " g c . a r b : a n migration the

Jlfage.r D e l ! a . ~ . , " ,( " ., -2@Seals in t.he NJger ,Diclta' .. 25Reservoir i c l ~ , t l i j f i q a . t i o n . "Structures and· B:YR-r9carbon , .accumulation ..,.' ( ~ $

1.19

1.17

1.18

1.20

1.21

1.22

1.24

1.25

1.26

1.27

1.28

7

67

2

4

4

1

1

1

tanning And Proposal

Major objective ..Planning a well ..\Vell types (Definit.ions)Well ,lrajectories (Planning

and Advice)Well path or Trajectory.

Horizontal Sidetrack.. ..International Geological Data

base (I.;PB)t . . . ~ , ~ r · 4Detern:ttnation of fluid ontacts 5JuxtapositionI COffirllunjcation INon-sealing between two (2)

sand units 5Why inject water into wells? 5

1d ntification of Hydrocarbon

h 'aring intervals ., .. 6I) t rm in lion of Hydrocarbon

tvp '(s)1.1 ti v sand

I I teroliLic lay r(s)

on1partruentalization and

HOlnogeneity of reservoirs ., 7

Net and Gross sand 7

1.1.

1.1

1.1;'>

1. I'

1.16

\.10

1. I I

1.8

I.

1. I\ .')

1 . : ~I,

Preface

D die tion

CHAPTER ONE

U fulness Of Production Geology In

Wll

v i vii



CHAPTER TWO

Log Corelatio:J} Techniques. Deviated!

Directionally Drilled Wells. And Multi

Laterals

ix

54

47

55

56

56

58

58

58

59

65

66

I f )

Hi

CHAPTER THREE

Well Log Evaluation

3.1 What is the role of a Petrophysicist

in tJle Oil and Gas industIy? 45

Net-lo-Gross ratio N/G). .. 47

Discrimination between sand

and shale .Discrimination amongst Hydro-

carbons. Fresh water and saline

water sands (brackish watersands).48

Inlerpretation of well logs- ."'"

Qualitative and Quantitative

QU[llita1.ive Evaluation of porosityvalues

Porosily. & Permeability values

in Ihc Niger Delta. . . . . 55

Radioactive sand. oil. water and gas.55Lithofacies scheme for th e NigerDelta.

Well Evaluation at a glance

Sand correlation across wells in atypical hydrocarbon field ...Gas or oil column ..

Isopach maps

Wire Line Logs, logs from

Measuremcnt while Drilling(MWD) and Core Analysis..

DetenTlination ofSaturation (S)

Qualitative and Quantitative

EVrlluation orWell Data

3.2

3.3

3.4

3.5

3.6

3.7

3.83.9

3.10

11

:1.12:1.13:1. 14

viii

'hicf objeclives of LogC o r r e l a t io n . . 29

Factors that can complicate

correlation .. 29

Log correlation Techniques/Tips 30

Faults. Fault cuts. Variation

Slratigraphy. and Unconformities 34

Faults vs. Variations in Stratigraphy

Pault cut determination 34

True stratigraphic thickness 35

Unconformities. . .. 37

Some checks .. .. .. 37

Relationship between structuredirection and stratigraphic

lhickpess . . . . 38

Deviation/Directionally dirlledwells. 38

llorizontal wells 40

Multilaterals.. 41

Applicat.ions of directional

drJIling 43

/I .,.o l

2. J

fl ()

..,n.n

,,,: \

:VI.: Ir1 • i 1••1

:l./I. IIJ.t! ,I

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1\. I ()



x

CHAP'fERFIVE

Questions And Answers Useful In Well

Planning. Proposal And Drilling.

5.1 Why do you construct structural

and sediment.ological sections? 93

5.2 Projection of Well in the cross

section is along stril<e. How done? 94

5.3 In the horizon map. why are some

wells proposed and drilled within the

boundary fault? 95

5.4 What is the basis for any cluster? 95

5.5 Distinguish between the Ol;ginalan d present flUid contacts.

WhClt are the ir implications? 97

5.6 What is BS & W? 98

5.7 What is the least separation

distance between two wells (allowable)

in a given reservoir? 98

5.8 Define the follOWing Drilling/

driller's terms usually seen on the

Driller's Planning report: - TFO:Turn; Build: DLS. VS? 98

"'.9 Gainma - ray logs for the

structural/sedimentalogical cross-

section give TVD and not

FTAH. Why? 99

b10

What are single. dual or multiplecompletions? 99

I I I Choice of drainage area.

I!orizontal well ranges between

91

79

8687

88

89

90

77

77

71

71

73

4.104. I I

4.12

4. 1:1

4.14

4. \ ()

4.84.n

4. 34.4

4.5'l.G4.7

CHAPTER FOUR

Well Planning And Proposal (Summary)

4. J Relationship between pilot holeand development well 69

Environmental Impact Assessment

(EIA) 70

Reservoir Management 70Advantages of horizont.aI wells,

over vertical onesUseful terms in proposing a well

Terminal dept.hs (TD)

Increase of Production/

development of reserves

SidetracksDefinition of some terms used

in Well Proposal

ToleranceWhy deviate?

ndrained oil/Attic oil

Commingle

S Ismic SupportTipS on the Production of Cross-

RCct.ions from Top structure

horizon map.

4.2



..I

(i I) Exploration/Pilot:

The e ar e w e ~ s drilled in a proven orr ognized firld. They e oft n of

g ological int ires t. and th obj iv L

1

C ~ T E R NE

USEFULNEsl OF PRODUCTION

GEOLOGY WELL P:L.ANNING

AND rROPOSAL

Major O b j e c t i ~ e :The main o b j e ~ t i v e . in SUlnmary. is lhedeveloprn nt air the reserve(s).

Planning a wJl1:Two onditio?-s lTIUst be looked at

namely: I(a) The type of well. Well types ar eWild at I D viated. V rtica!,Exploratioh/Pilo. Appraisal or

Deve1oprn¢nt. .(b) Often sOfe information on th e

enVisaged complet ion is mcblded,e.g.. i n g l ~ . multiple zone. or dualstring etc. I

1.3 Well types (Definitions)

(i) Wildcat: IThese are first wells in a virgin

rea.

1.2

1.1

105

105

105

104

105105

103

103

104

99

100

100100

101102

y.1000ft a 1

5 . 1 2 ~ What i s DFE?5.13 What is Deviation/Build up

rate? How:is the c.a1culation

done? ~ " ' f "' ... ..5.14 What ~ f l e t J { O P and EOB?

,5.15 W h a t j ~ ~ S T I ..5.16 S e i S ( J l l ~ 0 : , s U p p o r t - why?17 Whal.are th e implications of

1 shaliow hydrocarbons? 102

:18 What is collision risk? 103

).19 What is a n ( ) v e r p r e s s u r c . ~problem? ," .... 103

. .20 What Is the problem of shales, '1n tn t borehole stability?5.211 U n c ~ r t a t n t i e s ..

5 ~ 2 ~ Name th e mud logging types•.!1;' In the prognosis.. what does. 11569ftss or 11580. ftss.~ for example. mean? ..

What is plug b a ~ k ? ... What is inclination? ..

e seme well data for th e

u1 lecUve sand?5.27 I I do )O U detect thin

r H rvoirs?

5';2 are sandstone teservoirchar c-t ~ h s t l c s typical of the p I i J ; ' \ ~ ~ p a 1depositional environments?,

xi i

,.,



(Iv)

3.

~ l i ) :Depth map(stntctural map.

ifhls is a sub-surface map of the

.ireservoir of interest.

NB: In order Lo say co t . plan your

surface well location in th e already

acquired space.

(ti}lIorlzontal

Section:Draw your proposed horizontal section

where and how you want your well to

go,' bu t consider th e contacts. faults.

contours, th e drainage area for your

proposed well, an d th e adjoinin . well

(whi 'h should serv (' th conLrol).

NB: Mal e sur your horizon al section

land inside th e reservoir.

( ) Cross-Section:Draw your cross-section. (structural

and sedimentological) llsln;g 1VD .(Tr,ueVertical Depth) and not AHD (AlongHole bepth) from the Gamma-ray lqgs.

!'Insert the follOWing: ,(i} The wells (whether projected

(along th e strike' or not -Unto th e

cross-section).(ii) The contacts (GOe (gas-oil

contact. owe (oil-water-contact)etc.(Hi} The well trajectory and i n c l u d ~

the Heel and Toe (see later).

(ii i)

2

10 It" l 1b c lr ad . availabl

Pt OpllY. 'jea! da a and in t 11)r la ions.

ppraisal:'I Ill' > (3) or four (4-) wells are drilled in

n 'lei in order to appraise th following:

(:\) Number of reservoir sand ..

(1 ) Lateral e t nt ofth

hydrocarbOI.bemin ) sands, and

(c) Estimate of ih hydrocarbon in

place in that f luid.

evelopment:'[ 11 e ar wells d ri lle d in order toxLrac the availabl hydro arbons in

II I fi ld.

I . Well t rajectories (Planning and

Advice):n iUlportant que lion that fiU t be

:\11 w red is: Has the re s Ivoir b en

t l l ' in d at all and/or before? If lh

t i l l . wer is positive, then i t is necessary

I ( on ider if it is vii e econon1ical ly to

(I n in fu rth r. If COlltinuati n is valid.

II '1 planning will invol e th e follo"ving

II lJHl l :

( .I) M erials required

(II Lo(" lion Inap (surface filap)'Il< k if Lhe area of interest has

1)(' ' t l 'lcquired by th e Company.



(d) Co '":' ordinates:Determine the co-ordinates' of surface

location. pt'Oposed Heel (landing point).propOsed (Final point).

'- '

( ) Well path or Trajectory.

Finally, th e geologists will submit the

'o-ordinat s to the R e s e . I ; V 9 J ~ Dn ing

Engineers who will" use an adequate'omputer program to detenfiine the

I. J H e e l ~ the T o ~ , the KOP (Kick Off Point),

and "theBuild up angle HPJ, Some ofthese tenus used. in deviated wells willbe ~ l a i n e d ' l a t ~ r i.n the textbook as

t h e ~ t . · needs arise,f.t,Jr'H6rlzontal'Sic\etrac.k:.. . T h i ~ :is dr il ling a horizoritalhole from

an wexisting well into ane'xisting•. r e s ~ r v o i r where the 'oil is collected.. \see

" j'J' ~ e c t i o n 4:8 for mbre 'details).

l . ~ ' , J n t e r n a t i o n a l Geologi'eal riata BaseJi(lGDB):

t' . ~ ( i \ This is a Sands File storing suchI .. J.\4I- d' t Tihfor,mation, as co-or Ina es, ops

I'and Bottoms of sands. Fluid

.. l contacts, Deviation.. TVDss (True J

Vel1ttcal Depth sub-seal] TV ] ) (True iVertical Depthl,AHD (Along 01

Depth). etc, They are details of thstrat.a.

4

~(11) I t is stored in one server and data

can be migrated to another server

(software) using ASCII fonnat.

NB: 1VD = ftss + DFE (Derrick FloorElevation)

Ftss = Feet sub-sea

Ftab = Feet along hole.

1.8 Determination ·of fluid contacts:Original fluid contact can be

determined usmg Densi ty or Neu tron

Logs, while the present fluid contact is

determined by RST logging or MaterialBalance.

1.9 J11Xtapo$ition/Communication/Non

sealing between two (2) sand units:

Evidences are(i) $ame original owe value/S i .e

OOWC (Original O i l - W ~ t e rContact). .

(ti) Intervenitlg ' shale is no t sealing.(iii) Check'on the GST results for

POWC ( p r e s e n ~ Oil-Water Contact),

I. 0 Why inject water into wells?:This -. is done either for pressure

maintenance or for disposal intoshallow aqUifers.

5

.;r.1

L '



1.14

1.13·.11 Identification of Hydrocarbon'; V ,' , bearing intervals:·

This can 00 -' achieved using amhina(ion of lh e following:

(i) Shallow and de p resisUvily l o , g ~ .and

(ii) An overlay of tIl compu ted R 1 g

(from a porosity d _vi.c and tht:

estimated 'true' formationesistivity) ,and a RI\" curve

comput d from th SP uev aflercorrecting baseline drifl.

I.12 Deterntination of the Hydrocarbontype(s):

This can be done based on:

nOl' (1) The· t t ~ s u 1 t 8 o f side wall :sample::f' a n a l ~ s ' '·(m.arked ort -the-: PDLS

(Petrophysical Data Logs)" ' , I.(ii) WLFf (Wireliae:, Formation Tester)formation litessureS' 'and! samplesdata. j ' - ' ,- : ,Y, •

(Ut) The density"'rieu'trron overlay'. ,and-flv) Neutron count rate:: idVerlays for

gas - oil differentiation. '

NB: . Units. of - e a s u r e r n ~ e r i t forhydrogcarbons:

Gas-) nunscf (milli0rls standard

cubi fe [)

Oil ~ stock t ank ba rr I (3tb)

6

1.J5

1.16

I

Objective ~ a n d :This is sirrtPly the target sand or thereservoir interest.

HeterolitiJ layer(s):

Simpl , . sh ~ e s . usually charact riz cI by:(i] low pern7eability. and

(ti) llnes lIlat will reduce verti al

permeabrlity and impairproduction I.e. ct as baffles tovertical ~ o w _

C o m p a r t m ~ n t a l i z a t i o n andHomogeneIty of reservoirs:

(i) Camp r t nenta lj za tion

Simply, Fault blocks or faultcompart$ents.

(ti) Hornoge1eity

Almost homogeneous, implying

that we1l6 in th reservoir are incomn1uni ation.

N.B Fo r any comlTIunication between

fields. c h ~ c k th e followin6:(i) Well prodpction data,

(ti) Bottom Hole ternperatures andp r e s s u r e ~ .

Evidence: sinj1ilar or same results in

th e wells being considered.

Net and G r ~ s s SandGross ~ Totfll Le. and and ShaJ

Net ~ only ~ a n dI

I 7

I

I



N.B From the above. Net-to-Gross

ratio can be calculated. ifnecessary.

1. i 7 Mature Fields e.g. Niger Delta,

Nigeria.

With time and drilling activities insome fields, wells start pmducmg

excess water. This excess water iseither used for pressure maintenanceor disposed of by:

(i) Re-injection into shallow aquifersor

(ii) Channeling into the se a or ocean.

These happen in a typical maturefield.

1.18 Oil in Agbada Formation (Niger Delta):

The characteristics are:(il Paraffin type.(ii) Very low sulphur,

(iii) Very low asphaltene, and(iv) CAP!, 15°- 50".

1. 19 True Vertical Thickness (TVT) or

Expected Gross Sand Thickness.

This can be determined using any of

the following three (3) methods:

(i) Structural Cross Section.

(ti) Sands File (IGOB) or

(iii) FOP (Field Development Plan)

Update Reservoir Top Structure

8

map based on 3-D Seismic and

well data).

Method (i) - Structural Cross S clion

X Proposed/Planned- - - - - - ~ ~ = = - - - \Iv'ell path /Tra1"ctory

-TIl r·· ...."

Objl'Cli\ e S"nd or T"rget San

Iqg. 1. I Construction of Slructural Cross-section

using thicknesses (Ta, Tb, and Tc).

Prol(';edure:

Til. Tb and Tc are the gross sand

Il1fcl nesses a5 determined at the

Inte:I'sections of the well p.'lth with the

, \rious reservoir lOpS (X.Y.2).

NB: Often these values differ significantly

f'mm those calculated from the sands

!l



10

which

File

J I

(i) 7. 9 anel ] 2 are cxist ing well

had proper IGDS/Sandsinformation.

(ii) This is done for c\'ery reservoi,·.

Procedure:

1. Read off the Horizontal Section (Z)

for the reservoir from th e Deviation

Data Sheet.

2. With appropJiate Sca le ( that o f th e

Top structure map) measu re out

the reading of (1) above I.edetermine T (rnd o[ horizontalsection).

3. 1\rt [o r this reservoir falls between

that of well 7 and that of well 9

obtained [rom the Sands File.4. Inlerpolate (depending on where T

falls nearest (i.e (0 7 or 9).

This is th e proposed Tvt. This value

must be a whole number (i.e. not afraction).

I .20 Deviation Data:

These include the following:

[i) Target co-ordinates (Easting and

North ing) [or each well (surfaceand sub-sUlfacc).

(ii) Horizontal drift

(iii) Depth (nss an d Ilah)

Piss = feet sul>-:,ea

that pass

/)n)p()sL'd \ \'-l'I 1

Limitof thl' hydro('ilri"IHl

column/arcd foJ' thIs 1"t,:.''''L'nUlr

'9' 0 ' ~ " " " . ' . ,\ .V \:../ . . . . _. . )1 '

X ;<. _. .• . . _. \' ..:..\..>(.1;;\,,"... .. ' \t' ... , ·.,of\• t\-0\:\

oT

@,

Fil /IGDB [or lhe wellsthrough lhese reservoirs.

Method (ii) - Sands File (IGDB).f"W(.1J rrunn Top

Base ! GrossSand Iode AHBOF AJ-IBOF 'Thickness I(Reservoir)J !

X y I V-X lor each I,1 reScryoir

Jnd well..

Pig. l. 2 Construction of Cross Sec tion usingPDP update.

NB: AHBDI" means Along Hole bel,Q::I",

Derrick F l o ~ ~ F- ~ ~ ('''''''Method (iii) - FOP Update.

(a) Data Needed

1. Top structure map showing the

proposed well pos it ion. hor izon ta l

section along the well path. anel

Deviation e1ata.



J1)

\

k

Ftah = feet along hole(iv) DFE (Derrick Floor Elevation)(v) Build up rate

(vi) Maximum deviation. and(vii) Azimuth

1.21 Cross-Sections (X-Sections):

Basically, the aim of constructing across-section is to produce a 2-D viewof the sub-surface through line ordirection of interest.

Types of cross-sections are:(i) Dip - always advised and strongly

favoured.

(iil Strike - structureless. and

therefore no t recommended.

(iii) Stratigraphic - very useful.

For the purposes of this textbook. materials

needed for successful construction of across-section are listed below:

Protractor set square. Divider (forhorizontal scale). Ruler, GeologicalTemplate (1 :5.000 or 1: 10.000 scales).FleXible curves or French curves.

Structural/Horizon map showing the line of

the proposed section. transparencies,

leaner/Eraser. Masking tape. and Pencil(HB; 28 preferred).

The cross-section should contain thefollowing:

12

Fault(s) (boundary or any other). Verticalscale. 1-1Ol-izon tal Scale. Fluid contacts,

Azimuth. Wells. Horizon/Sand tops. Intra

Shales. TD of the proposed well. wcllTrajectory/ Path (proposed), Gamma-ray

signatures for adjoining wells. thicknesses

of th e sands and shales. legend. key mapand title.

NB: The following well data must be

included because a stratigraphic

(structure and sedimentology) X-

section is normally reqUired in

planning and proposing any well:

• Top of reservoir (ftss)• Expected hydrocarbon column

(ftah)• Maximum inclination (degrees)• OGOe (ftss) from density/neutron

logs

• PGOe (ftss) from RSTImaterial

balance calculations

• oowe (ftss) fromdensity/Neutron logs

• powe (ftss) from RST/Material

balance calculations.

Explanations:

RST means Reservoir Saturation ToolPGOe means Present Gas-oil-contact

co e means Original Gas-oi!'colliat'l

13



GOC

Wilter

~ ~ , , ~-_ fa

+

I_ Proposed ,veil

1\

TVSS

'depthi

15

o

1.22 DATA REGUIRED FOR WELL

PLANNING AND PROPOSAL

a) Minimum:

LSite Visit

ranput from T e c h n o l o , ~ & Petrophysics

:Horizon maps (structural with co-ordinates)

:Stratigraphic/sedimentological

sec·tion/structural section

I Location map/surface with coordinates

Scismic section with support

Section A'

"=snft' gnp (2/3)

b = safe g"p II ;, )

Fig. 1 .3 Conslruction of a Horizontal Section

fa met'e sketch)

~ W v " -. . .

1\'

0-- Pn ' r H ) ~ I . . ' d wL'l1A . / \ 1_ - I I ( ) r i / ( ) n t ~ l l Sl'Ctidl1 to d r ~ l i n

the oil tro1110

CD-- Q ) an.' vvL'lI:-..

OOWC means Original Oil-Water-contact

POWC means Present Oil-Water-contact

14

A

1.21.1 HORIZONTAL SECTION

The length of the Horizontal section isgUided by the following:

a) The potential Le. the reserve to develop

e.g. long section (higher potential[arguable) and more production).

(bl The structure and the sedimentology:

Choice of horizontal seclion



DWell data

[]nput from rese rvoir Engineers and

operations (drillers)

b) Others:

[Devialion calculations (for deviated weIll

[[Pressure prognosisJProvisional status diagram

1.23 GEOPHYSICAL PRO SPEC TIN G IN

THE SEARCH FOR PETROLEUM _A SUMMARY.

OUTLNE

(1) Introduction

(2) The accumulation of oil & gas

(3) Geophysical methods of prospecting:

(i) Gravitational methods

(ii) Magnetic methods

(iii) Seismic methods

(4) Application of GeophySics to PetroleumExploration

(5) Cost of GeophYSical Surveys.

1.23. I: INTRODUCTION

Geophysical prospecting ha s pro\'edvaluable in the search for oil and is almost

certain to be relied upon more and more to

find the oil and gas for the ever increaSing

energy reqUired for the transportation.

16

power, heat, and chemiral activit lcs of thepeople of the world.

1.23,2 (1) THE ACCUMULATION OF OIL& GAS

Accumulation of oil and gas occurs under

certain, rather restricted, underground

conditions.

Note the [allowing terms:-

(i) Oil '1'001'

Not an open underground lake bu t

a porous rock. more or less

saturated with oil.

(ii) Reservoir rock

, Usua lly a porous sandstone or

limestone.(iii) Source rock

Oil will no t accumulate unles s

there is a place for it to come from.Hence, there must be 'source'

rocks', usually shale beds

containing organic matter,

(iv) Cap rock

Oil would no t be held in a

particular place unless there wassomething to prevent it s further

migration from that place, Heney,there mllst be an impervious '('ap

17



GEOPHYSICAL METHODS OF

PROSPECTING

1.23.3

I,)

Any conceivable p ro perty or p ro cess

which can be measured or carried out

at or above the sur face and which is

affe ted by the nature or a tt it ude o f

rocks (or by oil itseH) through a cover

of hundreds of many thousands of feet

of intervenincr rock s may be made th eba is of a method of geophysical

prospec mg. Many principles have been

S1.l crested and tried but practically allthe geophysical search fo r oil dependson a very few basic physical principlesnamely:

(Al· Gravitational methods:

Measurement at! the':l$,urface: . o f ~ · s m a l l• variations' in .:the:;j ~ a Y i ~ t i O f l a 1 !lleld.

Tl1 refore, i f geoloo'ical movements

i valve rock s of diH ring densi-ty. th

r ulting irregularity in m . .

eli. tnbutjon Will mal< a carre. pan lit I

(vii) Traps

Thes'€.; are;- ·due· ')1fOL vnrf ty of

!Cj.,· I ge010gic ' p r o c e s s ~ ~ " , " ' t J r ('k

defonnations. Such d r n 11nll )11,are usual ly caJJed 'StruClllr s' . Toserve as a trap it is essenli 1 tl tthe structure be closed.

18

rock' or other trapping conditionabove or adjacent to th e reservoirrock.

(v) Migration

The oil indigenous to the SOurcerock is no t sufficiently-concentrated to make an oil pool.The required accumulation

necessitates 'migration of oilthrough porous. rocks and some

irregu1anty. of the rocks which willarrest· th e migration in acomparatively local area. .

, ., I

(vi) V o i d s / S p a c e S / P ( ) r ~ s J t y :Th.e spaces between the' grains of

porous rocks ar e almost never vJi dbut ar e filled with flUid which may

be 'oil, gas or water- either separate

·Or·-miXed. As, the flUids migrate

thr0ugh' tnep())rous rocks, the

lighter ones tend to rise through

an d float on the heavier ones. If atrap of some kind exists within

.which the migrating flUidsaccumulat e, they will tend to

e a i

densities, th e lightest (gas) at th etop, t.he oil next, and the heaviest(water) below.



pro 1 ing

II ('11 'ug(l l n bl

( I

surfac apalJl n-

8t ru tural reI'e[ jilt JI(

s-dimcnb whi h -'ouldfor th a cumulation of il.

(C) Seismic Methods: Ba I 11 tlw

mea 'uremenl of travel time rartificially indue d elastic waves. Such

way s. e up y explosives or by othersour or pub or continuous

aCOLl li" n rgy at or near th e surface.

trav 1 in L 11 directions from th e

saure =>s. Wa s having paths in cer ta in

dir ' ions ar r [rae I d or reDected so

th a hey OIne back to th e surface.

A senes of sensitive s e t s U 1 ~ d e t e ~ t o r s , .at the surface and at. vart01J1,$ distanGes

from th e sou rc e : c ~ n n e 9 t e d through

suitable . filters and ,amp lifi ers to arecorder. The resulting seismic record,

which may be visual. or on m a ~ t i ctape or both. proVides .th€ ' : < d a t a j ~ f o rdetermination of th e depth and form of

certain r e f l ~ c t l l 1 g .. or r ~ f t a c t i n g'horizons' in th e unde.rlipg rock .. s e r i ~ ' ,Under favourable conditions:, & ( i } ' i ~ i n i cmethods ma$' give information that can

be i n t e r p r e ~ d qUite s;imply and dttectlyin turns of geologiccQpditions" . .' I. I

v ri tion, in t he int ensi ty of gravity.Th measured variations are

I' • I interpreted in terms of probable

I " II subsurface mass distributions, which

in tum are the basis for references

about probable geologic conditions and

the presence o r ' absence of trc:psfavourable for th e accumulation of oilor gas.

(BJ Magnetic Methods:

Based on th e mea su rement o f small

var ia tions in t he magne ti c field. This

field is affected by any var ia tion in the

distribution of magnetized (orpolarized). rocks. Most sedimentary

rocks are near ly non-magnetic. but th e

u n d e ~ l in igneous or basemen r

usualIy flTe slightly magnetic. AsensItive magnetometer is used to

m'easure the re1alive o'r'absolute values

of magnetiC i n . t ~ n ~ i t y . T l i . ~ . s e · variation

may .b e measu re d at the surface or

more commonly, by suitable

lnstnunents 'carried in an aircraft. Aucost important result of th e

~ j J J l n . t e r p r e t a t 1 o m is the determination of

'l(depth r td the basement .rocks .and

thete.fore th e thickness of sedimentapres nL Also, i t is possible to'determin local rel ie f of th e basement

20



1.23.4 APPLICATION OF GEOPHYSICS

TO PETROLEUM EXPLORATION

The cliiTerent geophysical methods may

serve qUite different purposes in ageneral geophysical campaign for the

exploration of a large area.

E.g (i) General preliminary or

reconnaissance survey:

~ Gravity or Magnetic methods or both.(H) 'P'irsllook' at any large and relativE:y

t1111<1l0Wll area:

) Aeromagnetic melhod:

(iv) The interes ting indicat ions lhen

can be selectively tested by lhe

much more expensive. but

usually more certain. seimic

method or, in favourable

circllmstances. directly by

drilling.

N.B:

(i) There have been great changes ininstrumentation and advances in

interpretation, but the same (3) three

physical principles (graVity, magnetic.

lravel times) are still employed.

(ii) Inspile of many attempts to us e other

principles, especially electrical, none hasever allalned extensive field use.

22

1.23.5 COST OF GEOPHYSICALSURVEYS. (Econoniics of Petroleum

Exploration)I

(a) As a very crucle o r d e r - o f - m a ~ n l l l Hie

rule of thumb. the cost s per ml1e of

line of magnetic, gravity and seismic

exploration slanel in ratios of

1': 10: 100(e) The relative simplicity of its basic

concepts and it s a lmos t 'p ic ture

book' results in many applications,

have made the, seismic method

much t he mos t common petroleum

exploration method.

(d) Because of this and it s much

greater cost. seismic operations use

over 95% of the geophysical budget

for oil exploration.,(e) The potential field methods (graVity

and magnetic methods) depends on

forces acting at. a dis tan ce in amanner defined by the mathematics

of potential fields. (indirect/remote

sensing approach). This background

makes th ese method s much moreobscure and difficult than the

seismic methods to relate to geology.



·1.24 BASIC MATERIALS NEEDED IN

THE DETERMINATION OF THE

HYDROCARBON POTENTIAL OF

ANY RESERVOIR LEVEL.

0) Grain size motifs an d porositydata

(ji) Isopach (equal thickness) maps(iii) Iso-poroSity maps

(iv) Profile directions and weils(v) I ohath ( C]lIal depth maps)(vi) St ruet ural ll1:l{lS

(vii) Logs-Sonic. DCIlSily. Resistiviry-.Gamma-ray. SP etc

(Viii) Plots - Neutron p o r o ~ i t y- Formation denSity an d

Compensated

- Neutron Log- PoroSity VS. Bulk density

- Porosity Evaluation [rom

Sonic Log.(ix) Volumetrics

1.25 GEOCAP

This is a software package usefu l in the

p lann ing o f wells. It is . particularly.

u ~ e d in th e determination of R e a l i ~ U cl ~ l U Its (in effect. no fault is vertical).

24

1.26 H y d r o ~ a ; : b o n Migration in th e Niger

Delta of Nigeria

(i) Es ential ly Ver tical migration up

d ip alo ng fau lts from the kitchen

ar .as. an d

(ii) Lateral migration from t h ( ~ kJtehenarcas.

1.27 Seals in th e Niger Delta

Generallv. 2 types or se::lls/bc niers

exist in ihe Nigeria Dell a. na r lely:-(::l) Regional shales commonl. I referred

to as shale markers. T 1 , ~ higher

th e shale percentage. the better

th e tr·.:lpping potential :;. \150. the

t h i c k ~ r t he sha le s, th e hJgher th e

smear (greasy/sticky) potential

and. therefore. the ~ e ( ' tel' is th e

seal'ing capaci.ty.

(b) Fau. ts ( these display gr:lwth). But

fau li s with growth may seal If there

is !1Ufficient clay smear or i frese:voirs ar e j ux taposed aga in st

shales.

N.B: Oil trapped by faults. I t is

always advisable to drill behind t h ~ m .

j



27

(3) (Sedirnentary/Pinch out)

Unconformity

- -

Fig. 1 .4 Structures and O il accumulation

xXX

(2) (F,ulting)

N.B. 1.2 & 3 show different ways in which

struC":ure may control oilaccunlulation.

(Ii) Traps due to a variety of geologicp r o c e s s · ~ s and rock defolmations.

Such ddormalions are usually called·structures·. To serve as a trap it. is

(' sential tha t the s t r u c t u r ~ ' be clos-ecl.

---

---

___ Direction of General- - - '.."Migration

26

IMPERMEAI;I.1: ClIP

1.28 Reservoir Identification. Structures

and Hydrocarbon accumulationW l g ~ . 1.4 and 1.5)

(i) RED (Seed Grid (High amplitude

in Landmark Seisworks).

(ii) Remember to drill at the crest of

the structure (ie top of t h ; - structure/anticiline)



LOG CORRELATION T E C H N Q ~ ; . ' , t , ..DEVIATED /DIRECTIONALLV

DRILLED WELLS AND MULTILATERALS.

2; 1 LOG CORRELATION TECHIl'lQUES.

Chief objectives of the log correlation

are:

D ~ l i n e a t e sand' tops a.J?d bottoms

Delineate shale and sand units

Interpolate and fix faults (tnorethan 1aOOft throw is no t

sio'niilcant)Correlate th e s and and shale

units a ross wells and later close

Ifeltls in order'to build upstratigraphic hi tory/sequence.

FACTORS THAT C;\..N

~ O M f L I C ) \ . T $ > C O ~ L A T ~ O N , '"

Stratigraphic · t h ~ , o . i n g i

Beddipl, " I , . " "

Faulting

Unconformities

Lateral facies changes

- I Poor log q u a l ~ t y . {llldDirectionally drilled W ~ U & "

' .2

2

' + - 00 - -+ - - :\ I1licli 1L'

. I II ' .g. 1.5 Dtflflng the c r e $ t ~ r a 1 ? c: icline

(iii) Relnember that your stru ture must l e

amplitude supported (seismic).



\

NB: Closely spaced correlations generally

• Improve the accuracy of thecorrelation

• Help differentiate between faultcuts and stratigraphic variations.and

• Improve the estimate of the size(lnd depth of identified faull cuts.

2.,1 LOG CORRELATION TECHNIQUES/TIPS

orrelallon is dcfjlJ{'cl. as the

delermination of strvctural Qr

stratigraphic uni ts tha t ar e eguivale!lt

in time, age of stratigraphic position. ,for the purpose qf preparing sub

surface maps and crQSs section, the

two general sources of correlation dataare:

• Elect ric wirel ine logs. and

• Seismic Sections.

- No geologic interpretation can be

prepared without detailed elect ric logcorrelations. Accurate correlations ar e

paramount for reliable geologicinterpretations

- Electric Log correlation is patternrccognition.

- When geologists correlate one log toanother , they are attempting to match

30

the pattern of curves on on(' log to the

pattern of curves on the second lop;.

- Higher degree of correlation is ;lCill<'vccIwhen there are very similar pa It (,J'1lS

amongst the correlated logs.

- A correlated log prOVides infornlaUonon the sub-surface, such as:

• Formation tops and bases

• Depth and size of faults

• Lithology• Depth to and thickness of the

Hydrocarbon (H,J bearing zones

• Porosity• Permeability of production zones,

and

• Depth to unconformities.

- An incorrect correlation can be costly

in terms of a dry hole or an

unsuccessful worker or recompilation;therefore, it is essential that extreme

care be taken in correlating well logs.

- GUIDELINES - which improve the

correlation efficiency and minimize

correlation problems are:

• QUick - Log correlation i.e reviewmajor sands/sandstones using thc

SP or Gamma-ray curves.

31



• I,'m dl'lnllcd corrcln! 1011 work. firsl

('Ol'relale shale scct Ions

• Initially. use lhe amplified short

normal resistivity CUI\lC. whichusually provides the most. reliable

shale correlations

• Use Coloured penci ls to identityspecific correlation points

• Always begin correlation at th e topof the log. no t th e middle.

• Do no t force a correlation

• In highly faulted zones. I" correlatedown the log llrst and t hen correlate

up the log.

_The correlation patterns might be

peaks. valleys or groups of wiggles thatare recognizable in many or all of the

well logs being correlated._In highly faulted areas it is

advantageous to approach a recognized

fault cut from two directions:

• I 'l._ correlate down the log to the

fault. and

• 2'''' - correlate up the log to the fault.• l3y taking this approach.

dt'lprmination of the size and dep th of

32

t.he fault in the correlaled well will bemore accurate

- Log correlation Plan - Ask y011 n'll ,If 01]( '

of the several questions like

• Where do I start?

• Which log do [correI8te. 1".2"" and 3'" etc,'?- A good correlation plan involves thecorrel8Uon of each well with aminimum of two other wells (as closeas possible in the first place).

- Continue log correlation progressing

Ii'om wells in a dow;-.- structure positionto wells in an up - struclure position.

- Generally, corrclate wells located nearesteach other. In mosl cases. ' Closelyspaced wells should have a similar

stratigraphic section and so correlation

is usually easier.

- Initial QUicklook can be made byreviewing major sands. Sands are the

dominant and most obvious feature seenon the SP or Gamma ray curves. andserve as good quick - look cor re lat ions . .Because major sand beds frequently

exhibit Significant variation in thicknessand character from well to well and areoftcn laterally discontinuous. however,

33



35

For a fault-cut. there are 3important pieces of data:the size of the fault I' 'fthe log depth of the fault cut. andthe well or wells correlated toobtain -the fault cut.

• Fault size

This is expressed as th e vertical. 'thickness of missing or repeated

section

In. a vertical well. the logthickness and vertical thickness

are th e same.

Can be determined for horizontalbeds, dipping dipping beds and

deviated wells (see below).

2.4.3. True Stratigraphic ThicknessTST = TVTCoS(I)

• Where- TST = Tru e stratigraphic

Thickness

- TVT = True VerticalThickness of the section as

seen in a vertical well, and

W ::: True bed dip. " r

(a) F ~ u ; ; Size for h O r i z ~ p t ~ l r b < f d s- .l v J = J'Cep- Where

I ' •

34

they are no t recommendeCl for detailedelectric log correlations. Detailed electriclog correlation can be undertaken by

concentratingon SHALE SECTIONS.

2.4 FAULTS. FAULT CUTS &: VA;RIATIONSTAATIGRAPttr tJNcONFb1tMITIES

(FACtEs ~ ~ G ~ ) : ' , .2.4.1 Faults verSus,yadations in Stratigraphy

• The' differentiation between fault

cuts and variations in

stratigraphic thickness in wellLog correlation is very'important.

I. 1, If. a stratigraphically t h ~ n section1s correlated incorrectly as a fa111t

cut, this erroneous fault data Will

be incorporated into theconst ruct ion of a fault surface

map and later integrated Into th e

structural interpretation.

2. 4:.2 F ~ y 1 ~ Cu*. D e ~ e r m i n a t i o , n :By measu ring the amount ofsectiOn misswg in a ,well" on,e ,candeteimine the size of the fau lt by

CQrrelatjqn with another (nearby,if available).. well. This recognized

fault jn .a well is called a Fault

cut.

..



3T

w w 'It hOI" d viatio~ , ) j t ~ " l ' . '

I '. ,I I . t "'"'

." I j • . l,·r I "

where (<1» i th n

angle.

2.4.4 Unconormities

• S teeply dippiJig structures such

·as salt domes

• Excellent hydrocarbon ·traps

• Versions are:- Primary erosional., ", ..:.

'- Sonle D e p . o S i i t i o n J t l · ~ ... '- Qtl1er Qon1bjnatiqp. of both

• Appear as missing . s ~ c t i 9 n s on an .Electric Log. Therefore.' can bemistaken for a normal fault..

2.5 .sOME CHECKS .. ",

Structural dIp 9tty.O Q i t f ~ r ~ r i r ,above and below an un<;orifo.rmity.Dipmeter data can be used toindicate this cha.ng.e in dip. The dip

below an t:tncohfonnlty· is usually

steeper.

- If th e missing section is recogniZedin two or mote wells at. the saine ornearly the same c o n - e l ~ t i ~ e I depth,

an unconformity should besuspected.

- The amount of missing' sectionresulting' from an unconform i t

36

TVT = Tru· Vertical Thiel ne s

f a u l t s i ze )

MLT :::: Measured La f Thickness

in devial dwell

(I) == Angle of well boredeviation from vertical

• (b) Fault Size for DippinO" bee:,

- Depends n if this is requir dfor we drilled Updip ai

Downdipt.·- Whatever. you requir. pieces

data:-)1 The wellbor de\ iati n angle

(<j)) which can b obtained

from th e directional survey

[ th w II.

l( 1h rInation dip (»

obtain d from lhstructural map, and

» The il l asured Lo['"

Thickness (MLT) in ell.

that is equivalenl to th

mis ing section in Well Y.

Therefore

Cos(f) - (,) I) (U d' )TVT (Fault Size) =MLT . 0 P lp

Cos 1

CosCO 1 -

0 1)

TVT (Fault Size) = MLT (downdip)Cos



38

(ii) Common TYpes IMany complex I(a 'Iors go inlo lh e

design of a directionally d rl ll 'd w 'l l.

Most deviated w ~ l l s rail inlo Olle r twotypes:-

(a) 'L' shaped h<i>le (drilled vertically [0

a predelerrr¥nec1 depth and Ulen

deviated to aI certain angel which is

usually ~ constant to a total

depth (TO) of th e well. (FigS.2.1 or

2.2). I(b) 'S' shaped hple - With this, begins

as a v e r t i c a ~ hole and then builds

to a ptedeLermined angle,

maintains [lhiS angle to a

designated depl h and then th e

angle is l o w ~ r e d aga in , often goingback to vertiFal.

N.B Deviated \fells ca n also be

classified in10 three groups:-

(I) Wells dril led down-dip(ii) Wells dr i led along strike. and

(iii) Wells dli led up-dip

II

I

J9lI

111\' LI p-sl ructu rcncreases in

direction.

DEVIATEDjDlRECTIONALLY

DRILLED WELLSDefinition

A directionally drilled/deviated well is

defined as a well drilled at an angle

less than 90" to Ule horizontal. W ll s

are normally deviated intentional ly in

response to a predetermined plan.

Straight holes often devia te from t; ,e

vertical due to

(a) 8 ft rolation, and(b) Natural deviation tendencies

of sub-surface formations.

- The stratigraphic !:Jcquence g e l ~older in the up - structure direction.

_ The sedimentary sequencc just

above the unconformily is younger

in th e up-structure direeLion

RELATIONSHIP BETWEEN

STRUCTURE DIRECTION AND

STRATIGRAPHIC THICKNESS

• Up Structure Direr-lion ...... Constant or

Reduced Thieknes

• Down Structure Direclion ~ Increased

TI,rrkn 55

(i)

2.7

2.6



...;, I rl<1t.'('

Dcrl\'atil!rl

t \ n ~ k '

Fi,t(. 2.1 (.1) l ) ( , I ' ! n k t l / f ) i r ~ I ' t i o n n l l y c1riil<.:d IITIl

CALCULATION OF TVD FROM AHD IN

DEVIATED WELLS (Fig. 2. 1(b)

<D

AHTva

TVD =AHD Cosine <I) \\'Ill'ft. til::: dt'\ i,\I,on.H

TVD =AI-ID COSillt: (1

wiler· 4'= cI vial ion angle

2.8 HORIZONTAL WELLS

'I 'll ' ~ ; ( ' also belong to th e class of

c1('vialccl/directionally drilled wells.(Figs. 2. I., 2.2 , and 2.3)

40

I ' ~ ~ I -+-11,"17<'lnt"I-+s.....liull

2.2: f-!ol 'iwnlal well

2.9 MULTILATERALS

(13) One vert ical and two horizontal wells/arIJIs.

The vert ical can be deviated also.

fig. 2.4[a) - MullilaLerals showing various [11111

41



44

li'ig. 2.4(c) Multilaterals (Contd.)

WELL LOG EVALUATION

4!1

CHAPTER THREE

What is the role of a Petrophysicist

in the Oil and Gas industry?

The objectives depend on differenttasks in the different stages of the

reservoir life cycle, but at. the

exploration and appraisal stages, t.hemain job is the quantif icat ion of the

volume of !he hydrocarbon in place.However, tJ I·j,.; is done in conjunction

wi th the geophysicists and geologists.Logs which are used to quant ify the

hydrocarbon in place, can be classifiedinto three ramilies:-

Reservoir Thickness (Gamma Ray,Spontaneous Potential). These logsdiscriminate reservoir from on

reservoiL(8) Porosity (Density, Neutron, Sonic).

These logs are used to calculat.eporosit.y. identif'y lithologies, and

differential oil [rom gas.(Cl Resistivity (Lateralog, Inductiol1,

Microresistivity). These logs . toge! IW I

with pOl'osHy logs. are lIscd II I

calculate hydmcarbon ;saluralionf-!,

::

,I 3.1; I j I"

":

I :l:1 ,.......... .;

r:J ~

:' }.

::-: .

I 1,1(A)

;

'""."

E:t c;.'"

0be .D ...

t E c g o ~g u: r- N U>"'S: (f) '" !'J

N _: 2 u. - "S:- .2: :r a ;;;, '" I ';: ~ - , " , ~ ":e-;c: , '-'' " :J.: C: I B -. , .L..""Q.J.. ._a ::e::e l:-;c: 0 ::e ... ml../)

", c .!:j C :J;:'" N

1; 0:J .;:;r: 0 0 I 0

l: I

m 'v 11.1 t

j <3 H:"'

J \\IIH ".'", 1: t' .

";

:: -

0 0

'l; "-:'

-.-, 1 I

.J/ i - I i.:,

11;

;;,;

:;,

f

>LJ

-I I I f--I--z

<;;0,;

o

ZI.c \ ', T

o.,

c:::

Q.o7,

-r.'J )

'"

-Gwr->lJ.'/.

...U-'...

...VZov

9' .



I hi" ,,(oJ • n,..J !>(';l" .,,111<-

1"'"lull) ... ~ " h . · . 1 1

\ , , \ '!!I.t. h-,t ".1,111,1. ,J

Tru(' (onn,'1lil'lI pr of ile------ log response

- - - - - Blocks u s ed f o r evaluatiOIl

Ot.hcr ly p 's orWireJine lools a n ~ : -(i) Siele Wall Sampler -

Takcs sma ll rock samples. which are

used for lithology and I luid type

confirmations

(ii) Formation Tes te r -

Measures fon11alion pressure!:> and can

ret.rieve fluid samples.

(iii) Dipme te r -

Measures dip and Azimuth 01" the layers.

(iv) Well shoot & VSP -

Used to calibrate seismic

N.B: Large and irregular boreholes (;an

adversely affect the accuracy of the

measurements. The log correclion needed in

these cases can be quantified using

approprial e charis.

3. I. I Jad ing Log Responses

1\11 lools hew a l imiled vertical

I l ~ s o h II ion. los to ii I hology boundaries,

11)(' II I ':11")111'('111 'n(s will be affect.ed by

nd.lil{'('111 beds. In very thin beds this could

I 'ad 10 lool responses which d c v i a t ~ from

Ill(' I rue forma ti on profile. Fig. 3./ is a

lccl1lliflllC useful fo r reading log values of

acll 'constant' formation bed. These values

can b ' used to calculate the petrophysical

parameters of each bed.

4 6

Fig. 3.1 Reading Lo,£( responses.

3.2 Net - to - Gross mlio (N/G).

Gross means total thickness of the

reservoir ie inclUding shale while Net

refers to the sand/reservoir only. (see

Fig 3.2, Gamma-Ray log and Tab le 3, I- Tops and Bottoms).

3.3 Discrimination between sand clncl sll:II ..

(see Figs. 3.2 and 3.3)

47



2 I X 12 62 3.3 12653.3 13 0 I 173 I X I 2591.4 I 2616.4 I 2; ' I I I

.- SW I I X I 2691.0 I 2722.5 I 31 I 2 I

H

Gil (MI)o'\11 20 JfJ -10 ;(1 I>lI 711 'III 11111

1800 J ~ _ J __ . L J ~ r -[LI ..(:.... _.! iii j (

! ; $11 ;

, : 'I, " .,);: ' ' ! , j'-- ;.-.- ...;...,.. - _., .. y ' .- -.-

j ~ ~ ~ ; : - .

J - · i ' - - ; ( i J , · t ~ ~ D ! · _ · ; - - - : - - t - · - l i\ ' • I , ( • I'h

-to_or t ~ : - t - j - - ~ · - - ~ - - r l ...: ' r ~ { .1 ••

-\ .. " ' ' f : - : ~ : . . r . · , · , \".' ...., i ( i j

; J ; : j : _ > ~ ; \ U ~ O ; I I ! r. _ ~ - h . ; __ •. i._ - , l . - - ~ - - 1 · " ' ' ' ' ~ .. '.i ~ ~ ' j ~ J I ;: ; : l (. I

· · i · · · ~ · · ~ - + · · r · · · ; · · - < : · · · ~ · · ~ · · ·, I"'". SAND

...h·

'T":' -: .. .. ·i: " i - ' ~ - ' - ~ l - r - "I \ I < ,. J

1810 f - · ~ __ ·L - "' - -, • •,---;-_, • __ ..

I ~ . _ ~ - _ . ; •• ~ ~ ••

i ' ! \ ' I" - ; - - " - - c r r l , - ~ .. _._._, .. - ·... _L .D il\L.U: ~ . ;

; \ ! i i. j. I I •_ . ~ _ . i . . ___ ~ , _ . : . . . . - . : , - ' ._L....::c....-.J

~..cE 1805~

49

..c

0...OJ

Cl

Shale H,lSl' I.in" (50 API .. Mid-wav)

I··ig. 3.2 Discrimination between Sand and ShnJe.and relationship between Nei and Gross

thickness using Gamma.. ray Log.

- -

lEVELELL NI\ME ABSOLUTE DEI'TH ' TliICKNESS I THICKNESS:

TOI' 1m) Iml I ImIINET) I1 - _ ~ _ - - l - __ + ~ _ ~ + B : : : O : : . : n . : . . : : O : . : . M + (GROSS) I --J013AGI I 2609.2 2631.7 22 ~ I

17 I " I 2656.0 I 2666.0 I 10 10

3.4 Discrimination fo r various combinations

of rock types and containe>c! Ollicls (see

Pig 3.4)

Table 3. 1 TOPS AND BOTTOMS OF RESERVOIRS

AND THEIR RESPECTIVE THICKNESSES

48

.. 19" 2073.8 2707 .7 , )4 24~ 20" 2615.5 2040.1 12

.. ~ : I ' 12.7_ ~ 1 J . : 1 2H 18

1 -.. X 2lillH.a 271 :l.1I :! I 7

- --. <:11 X <:0:32.:1 2G47.2 15 2

.. :31 .. 2U<iO.O 2677.0 17 6 I

~:1'1" 2G0:2.H 2627 .S . 2S I j I ,

.. : la" 2671.9 26RII.9 17 16 I

, , ~ O " 2607.7 2626.9 lH ! ? I--<013AGISI X 2616.9 2641 .925 11 6 I

.. 4 X 2585.5 2510.5 12 5 I 16

.. 5 .. 2609.0 2G21i.7 lit< 14 -

I" 6 .. 2606.3 :263•. 3 -2 8 I 14 I

I" 7 " 2581.5 2606.H, :2S ,1;< -j

8 " 2660.R 269·1.1 I :J :J i 23 :

I .. 13 " 264.6.2 2674.2 T:2H I 13 , ~'.. 14 " 2057.8 2690. IT :n j-;;; II OBACI 15" 2622.7 2652.9 I :30 1:20 --1

.. 16 " '2650.6 2672.G I 22 t 6 I

N.B: Net - to - Gmss can be determined anclthe n:sel"oir appraised properly/correctly.

Exercise:



"

\

J

...

_-...

;'::": 1

I

"

\

)...., - -!I

~ D

. ::..'.1'~ i = : : : ~ - ; , ",. I"':: " , , I "" " :i r ~ ~ MI t,]:::,:.:·, ~ ' ,.!," l j '-·, :..7.: .?ij}' I (. I,_,'r -- rr.=':::::-'" I ' - - - .~ ; f ; " J J"'"b : ' ; ; 2 ~ ", I J ,--\:",.,0'/:\.: (-f' 1\~ ' i ; , t ; : ¥ l ' " I -; i ~ ~ ~ ~ ! ; : i \ -H I1-':.':':" I : ': ~ ~ ; - : ~ I \ . , . I I~ - - . . ; : : : : : [_+. I

'- ' 1; - ~ < i i ; (". I I /:=. c··A ~ Ir£" -

I

I.I

I

\11:IIe ..

\h;d.\ ~ : ~ : = I\;1·,<1 C:'

\h.11e ~ : ~ ; ; ; 1.==- ..

I , t ' ~ h ~ . ,\\.';lltT ~ _ ~ i- ..__ ::::::::.--",I -= ; . . - ~ .

)ddk ~ - - - - -t . f , ~ ; ; ; ' ~~ , l ' :::;v.'.. f . > d . I ' \ j ~ 1

Oil !(d·,,\!J\,'\1";','4! f ~ ! : I . : , I " L ,;\ ; ; , i , , ! j , ~ ! '

\11;1/(' i ; ; ~ - :; . : . . - r

~ ; d tW ; r ' l T ~~\halc ..::. : : . ~ _ .

.....:.. .:..:

I

I

51

I,

.- ":: . . : ~,halc ..:'" j

"'ig. 3.4 U ~ i n g R e s i s t i ~ i t y an d (Spontaneous

r 'otential Logs) to identify O il Fr esh watcr ancl

Saline watel ' sands. an d Irock types.

( ,r:-.h,dL'

Sh.lk,

-

( . , IJlll l l , l-r.l \

Cr",,, nd

50

Poro ... ity

r 'ig. :J.3 Saml/Shrl lr discrimination using

porosity an d Gammrl-RrlY d>1trl.

(i) Calculate the fraction of th c reservoir

within the total sand sequcnee (ie.

Net/Gross) given as Ij{; = (!I, + !I,Xt )(ii) Determine

(a) Tops an d bottoms of the sand (reservoir

sections)

(b) Thicknesses of the individurll sand

layers (Ii, an d h,)

(el Total th ic k nc s s of sand (= Nct reservoir)



(12 n".I.u ....l l' I l l" '" touo

'illl4d'ltllili' JJIDi-'l'" 1: 1II lIlW!!.'"111 ,- .1!1ihf , !

j 1.1111 'I--- <'u· .,I t !TiT I : - ' . ' ~ , I Jh II ..

11 '1 i;;'" '" JJ.!1 I • I rF.T1"j

I 11

111 t i t ' l l,mll I·q: 1

mill ljll! !I i l l l l l ' ) :III ' 'I i 1 I' 1 I" ! 1

I " * ~ I 1\11 i ~ , , . . , ~ ~ ~fi 1111 I t ' : I ~ :II II " i ~ _ h ; ' ~ t l : ~

III 1 ,I ~ ' ~ " 1 < ' ~I 111 Hg.;,; ( ' l ! ~'I I II I ,II l li,l. i

I dill III r 1/ lid; ;n lit I III i 1I11l: 1,:11

11111 :iill :111111 11'llI II Il i l i I II ; l:'ll

11111 I ill I IIILilllIl :

~ 1 1 . 1 I 1 1 1 1 l ~ 1 1I" II!!I ; l I 1 f f i T T ~ ~ ;

Will ! lIBI dltlm 11::l!l I

Hllll '!Hi 'I i !Ill' I , , ! ~ r .

I iiII 1 l 1 ~ II I II! II ;rfiififl Ifill 1111 mI tr:HU

r r W ~ l l l i ll I l lt i ll . I li' liTiIlilll ' Ill ' ' 11 11 Ul I 1'111

f t i 1 ~ i l ~ ~ ; i j ~ ~ ;ttUfflr i J i j I I - - : - r i i j [ f n ~TTTTJ

TTI : l

,I

-++1.,,

!I!:. : ~ . 6 Ii) DiscTiminal10n as in (Fig. 3.5),bu l further [or cvalu<llion. Density

10.;( is included.

53

, ; : : : ' . ~ ? ' ~ - , ~ ; t ' !~ ~ e ; ' ' ' ' ; ~ , , ,

_ ~ , [ ; ' . ; . ~ : ~ >1' I i

. ''<:1''$:' d - ~ - = S . -\ 9 ; ~ 1 I ! I I i I 1'"(

I J l -LL 1± ' 1 ,~ L _ I I I .J ~_.1' U ~ I " I_ I T J ' ' ! I J IS' .L.L.l '1'1"~ -l±J ' I. , .. ~

J; -l I

{." f+Jffi1820 I . 1 1

m'.'··\''.:t±iTIJ, ~ m

G>.."TTi1 l ! It ! t

fEW!S 3 C b ~ 1I I I gl I; i I .J.J

. ' - I-'-ttt ItI::I: J

52

_:', (",\: O ~ " I I .. . ' , ~ ' w - " j r ~ ~ c ; ~ l ; ' ; ~ ' i i : ! : ' : V : 7 ; ' :".1" ; l : : > J · : ~ j . V .• •

, l I ''. I ;5·S") 1 )

- - ~ ~ i l ! ~ ~' , I 1 '. , ,

r : I -' '· 5 JL__!.,... 1 \ __ : , ( I l (

( I '. ~ - U'I" , t,; /' t . ' lh · 1- LIII1[I1( '

(I! \

" . I ' ' ) I........ , ' , ,), - I") ,I '

! . i ' •

c.;'-1 -J-_---L- _. ( - O..!VC: i I\ lll)il -\'Volt',- C"nt.le:)

I : I r ,.' I,. . I I(Sf" _.' ! c.; :. ~ - . ; - )

- ~ [ r-I I~ " l (. \, Ik·o I \

IFig. 3.5 (il Discrimination between Gas. oil.

salt water using Gamma-ray.

Spontaneous PotenLial RcsisUvity and

Neutron Logs.(iil For oil. gas. and W<lter and·their

contacts, ResisLivity and Neutron Logs

are ideal.

QUALITATIVE EVALUATION OF3.0) " ~ ~ •..!•....;:lL'.. •. ;-,"";"__1'1. _. ~ , .. ~ : , - 1"""';



54

Qualitative evaluation

Nea:JigiblePoor

Fair

GonclVerv Good

Excellent

POROSITY VALUES

% POROSITY

0 -5

5 - 10lO - 15

1!'i-20

Ovcr 20 - 25

More than 30

55

3.7 POROSITY AND PERMEABILITY

VALUES IN THE NIGER DELTA

(Omatsola, 1982), lor reservoir sands

of [h e Della.

•r ~ e s i s l i v i L y

of radioactive sand isapproXimately equal to that of shale .

so there is [hat problem of

.. Poorly (,oIlso!id,lteci

• Porosities as high as 40 1% in the oilbearing sanus

• PoroSity reduction with dcpth is

p:radual because compaction increases

wi t h depth (i.e density increase),• Shallow sands less than (300m) have

porosity greater than 15%.

• PermealJi li lies --_ .. I - 2 darcy range inth e I-fydro('arbon rcservoirs.

3. 8 RECOGNITION OF RADIOACTIVE

SAND, OIL, WATER AND GAS.

t;.';,"

··W'I ,

71:: ' i+-u

';'iTJ-".

•/k-Li-+--"rJ

ualitative

...!

I Quantitative rlI

Use 01' 11l'1thelll<ltil'alIllodc:j,; Irl'1aLions LO

. I

1o(('t values for th e I

I()rlllat ion paramt ' l tT " r

(pclropllvsiCfI!):- I----porosit\l I

---pernlcability I---saturatJoll.

I INote: Sec Section 3.15 3ncl3.16 fo r morc delails.

Fig. 3.7. Straligraphic CorrelatioIl of \ V e l ! ~ i i '

Niger Dclta oil fielci. lEI u-Efeotor. 19871

~ , : : ' : . . b ~ · 1 . . .

\ :( ..j

} I j ~ : . ] ! , - i v , ,<C

Visual icielltificaLion.

classlficatioll ilncl('onlparlsoll 01' sal Ids.

silnit's. I'nvinlllllll' lll ofdl'pllHi lion [1I1t1 nI lid

1'11[1 mell ' rH/ responses/

('OIIIHl'ls based 011

similarlog signat ures.

3.5 INTERPRETATION OF WELL LOGS

disl inguishing bCtWCCII shale and



sllch a sand.

• I ~ c s i s l i v i t y , Density al1Cl NCLItron

Porosity logs arc rcqll ircd all to.L(cl!1cr.

• Thc best way or !·cco.L(1l i Sill,!!;

radioac liv c s ands is Ih< lISC or

Spectral Gall1Il1,1-ray lo.t':s.

3. 9 LITHOFACIES SCHEME FOR THENIGER DELTA

011111

Or

Ohm 1(-("

Volts.

I ~1----1

__-.1 I

Electric';11

n·:-.b/:IIlC·I·.

n· ... i ~ ' i v i ' . Y

V l l l t l l ~ C '

Wh:lI Is lJllih

tllt',IHlll""d of

111(' rorrll;,1 i l l l !

N;l1ltr'Oil 1\1 'I 1ttlils

t!H It 1I1t;1

r;l( li;11 io n

I 1·:lt'I'lroll (;111/('('

Ikllsilv

f'

IJ r y d r o ~ ( ' 1 trkll:-.itv

•

r d ~ ' 1 1 1 i fyll II-!

: - ' V l l l h o J ~

' -I '

[.1,1) Ik"p

I IW; I ...III 't·ltlC'lll

l (:NI.

L

I,',c

In general. lor Ilydro('arilolis (oil i l i id

gas), rcsislivily and dens ity I ( ) , ~ s ;11111

correlatc.

Logs, identifying symbols. What is

measured of the Formation. and

units of measurement

0) ( i ; lI l l 1 ll ,1 r; l ) ' I ( i l ~

1 . J ~ l . ) Shallow

111l': 1"'11 n 'JlIt'1l1

P>7

nj) IIl 'n ... iIV 1 VI l( :

(iv) HI'..,'...,1 iVll.Y I M ~ F L MifTII

tlll·;I ...lll ' l · llll·ll!

IvlSP'Hlllltll·IJlI ...

pOII'111 i:d

\ kn l ri l l I

(2)

(.I) The dceper readin,1..( lo ols arc L1sed (0

inclicate il' a ~ o n c is waler (l 1

hyd rocarhOll I)C81"in,l..(.

N ,B;f)"IJI i ls o f IIIV",,1 i . ~ ; 1 1 I o n vis· i1-vis Hcsisl iVily L o . ~ s

C(HTe It II (.

Pore Ph I ids

I)vllsily-)

kh'C'lnlll

( h · l l ~ i t . v l

;1I1<l

56

) Iit-slsl iVily "11(1 1 J ~ l I s l l yIl ' I I ' i ' I l 'OII

clt ·t I . il vi

---? dose: 1I1e!

sindln,-

I { ) g ~ ill

,il<lpe _

O p p o s i l ~ 01'111) N"l I lml l "m l I ) ~ f l s i l ylogs; l l l l i - ('oITcI.li ('

l.illlOl:H'it's S:lllrl 'HI SIJ;lI{' 1M. '('utaloJi)

COlli Ill ''Ill: Ii(IknillllwltI:llllJlt) (YO 10 100

Trn nsil iOIl<l t HO 20 100

P<tr;llic

ll\gllad:l FOl'tltalllH1) GO 40 100

Mnrillc

1"1\:11:1 FOI'Ill:LlhllJ! 20 HO lOO

WELL EVALUATION AT A G LA NC EUSING DIFFERENT LOGS

Uscl'ul Discrimination be(wecn

( f o \ ~ s . 3.!'5 & 3.6).

(III Oi l N('\iI mil

III) W"I,"

((') C"s

3.10



58

It can thcn be deducted as foll()ws:-

59

TI,c downhole mC'asuremenLs are

perfo rmed with logging tools. The arephySical devices [sondes). working withvarious principles (or nuclear.electrical. acoustical). lowered in the

borehole via wireline (wireline logging)or as part of the dr! II string (measuring

while dri lling (MMTD). logging while

drilling (LWD). aI' formation evaluation

whHe drilling (FEWI)) . In some casesWh{,ll wireline l o g g i n ~ is difflclIlt e.g isstrongly deviatf'd holes, the tools C<l11

be lowered (aftel' drilling) wi lilt'

sclccted silml unils in dil'Jerl'l1l wells,OJl a bl a n l( n1<1 p.

:1.14 Wire Line Logs. Logs from

Measurement while D r ~ I l i n g (MWD)

and core Analysis.

LOl!;S or any (ypes scan be measu red

after l l1e drillml!; (\Vire Line Logs) (see

belowl ancl rllIrin.!.\ the drilling exercise(measlIrement while DrllJingl. These

days allrl in oroer to save costs , MWDis standard. Typical MWD Tools are

(j) Fnrm;;dio!1 Density Tool

(ii) Ncu Iroll Log Tool

(iii) Sunic Log Tool, or

[iv) Dipl1leter Tool.

best responds III

resistivity rind denSity

logs.

---tiii) Waf"r

(i) Saline' water zone'o> - ) Low r lsistiv iLy or

l l igh l ')llcluclivity

(il) Oi l f\l, I Gas --t best \ 'eSpllllci to neLit ronand dl'nsity LO!l;s, hu t

(b) In general. resistivily is high inhydrocarbon zones, and 10\\ in water

zones. and(c) Formatioll water saliniLy and porosity

influence the readings. and fresh water

zones can resemble hydrocC1rb011

l'I:i>ervoin, .

3.11 SAN') COR.RELATION ACR.OSSWELLS IN A TYPICAL

HYDROCARBON FIE·LD (FIC. 37).

0.12 Oil/Gas Column

f'dl11ply l prod1\e( of Th iekness (Net)

"ncl nvcnI/!,c porosity. WiGS. 3.5 and 3.G).

:3,13 Isopach Maps

T11('sc ::;how the lbjclt'lf;SS of sand :.milsit l different wells and a re used to study

:->lructum.1 g;rowl.h. They are preparedby con1::Jurlng the I.hickness of th e

I



connccled 10 drill pipe. 1)1' coiled lubin,g,

This is somc( imcs Tnlle;11 LO,l",gi n,l(

condilions (TLCJ.

al len togging is curried oul by

contraclors. Thc rn,lin Ioggin,g

conlraclors arc Sehlumber, l(eL Western

Atlas (WALS). and Halliburton (I-I LS) ,

Important LWD Conlra('[ors ~ r ( 'Anadril l (a Schomber,ger company).

Spcny Sun an<l Tdeco. Ev,l!vat ion ~ l r cc;lrried out by in-house by the main

company like Shell, which has its

pctrophysical so!lw8re package

(LOGIC).

Core Analysis measurcments (porosity.

permeabil i ty, grain density) can be

carried out correctly by most scor('analysis contractors c.,g Corelab hu !

dala are always aud il ec l/cl1cckcd by

main company that has the contract in

her own laboralies,

I';ssenlially Win' l ine I>ogs ar c used 10

<l1'll'Il1lll1(' lh e reservo ir par8meters.

r';xalllplc's arc Sponlaneous Potential

(SI'), GWl1ll1a I ~ D Y (GR). Df'n!-'ity (POC).

NClI lo rn Log and Dipll1cter t o , ~ s . The

potenlial and procllleibilily or a

n ~ s e r v o i r dcpend on certain

characteristics and propertics which

60

include porosity, pCI'Ill<'a!>illly, gr;111l

size. grain shapc, ,gra in ('Olllp;1('11011,

malr ix and cemcnt compOIl('lll o( III('

sand body. Thc logs arc 1)/ Idly

explained bclow:-

3,14. I Spontaneous Potential (SP) Log

The curve records the electricalpolenlial (voltage) produccd by thc

inleraclion or rormalion conna le water.

conduelive drill ing fluid and certain

ion-selec li ve rock (shale), The shale

basc l ine rrom which the Sf> deflcclions

8rc l11easurcd is lIsllally fairly del'ined

on the SP IO,t(. Thc SP CUI-VC has a

nUI11:Jer or usefJl! ru nct ion s which

include correlation lit hology. porosily

and pcrmcilhility indications 8nd ameLlSIm.:menl or (form8Uon walersalinity).

1\ Iypical Sf> log s llows deparlures to

th e Icn rrom a base-line or shalc-l ine

reading on the right, to a sand l ine on

thc Icl l in the 'cleanest: non-shale

zones. SP defleclions a lso respond 10

depositional sequenccs where sorling.

grain size or cement at.ion chanc;es wi l hdepth. The shapes ar c also callcd /)ells

or run nels.

6]



3.14.2 Gamma Ray (GR) Log

This is a measurement of tile natu ralradioactivity of the formations. [nsedimentation formations. the lognormally reflects the shales. Clean

fomlations usually have very low !evclof radioactivity, unless radioactive

contaminant such as volcanic ash or

granite wash is present or the

formation wat.er cont.ain dissolved

radioactive saU s.

Gan:llna Ray (GR) Logs me used for 4main purposes:-

(a) Correlation and bed boundary

determination.

(b) Eva luat ion of the shale content ofa formation.

(c) Mineral analysis, and

(d) Perforating depth control and the

tracing of the radioactive fluidmovement.

3.14.3 Density Log

This is t.he pr imary ind icato r of

porosity. In combination with other

mcasurement, it may also be used to

Indicate lithology. formation lluid type.evaluation of shaly s a n d ~ .

62

identificat.ion of minerals ill l'v;lporilcdeposits. detection of g;I.."

determination of oil-sl1ai<' .I'11'llI,

c alcula tion o f overbu rden pr('SS\lI<',and rock mechanical p r o p c r t i e ~ .

3.14.4 Neutron Log

This nleasures the amount of nitrogen

in the lorllmtion. The neutron and

density l o ~ s have Ilrst order

dependencc on l i t h o l o , ~ , porosity and

flufd contcnt. of the formation. The

presence of shales/siltstones in the

matrix has a partic!i1arly strong effecton the signals because clay minerals

integra te valuable amoLlIlts of water

with smeclil es (swelling clays) thathave important volume variations

depending on thei r wat er con tent . The

neutron tool detecls all water in the

form8tion, including bounding water

associated with shales.

:U4.5 Dipmeter Log

Dipmcter logs record ways in which

subsurface layers of rock have been

depos ited and su bsequenlly movC'( 1.

The raw data consists of orient<lfhJIIinformation an d corre];\ 111111

63

presence of .!.(8S



J,

11111111'I1CC or

Water

&11 IIr:11lO ll

ClIVi! Ollll l( 'nl ;1i

COl I (.(., lOllS.

Secolle! Arehic

cqU<11 iOIl ( I I)

65

J,

Plrsl Arch if '

eqllatiol1 (I)

Influence or

I'orosily

Determination of Saturation (5)

(i) Defined as the rraction of porc

volumc

, . s". =I -S"

Where S,,,=hydrocarbon s;lluration

and S,,= waleI' saturation

(ii) Use Archie f lo r waleI' bearing

rocl(, and

(iii) Use Archie II lo r hydrocarborn

beahng rock.

conditions and .!.(8S

tempera t ure and pressure.

But consider the followin,!.(:

PoroSity.Resistivity of the formation brine.

Water content. and

Amount and type of shale.

N.B. Archie equations combined.

I ~ e s i s l ivity (H,J

Measured by

lAJggi 11'(( Tool

3 15

/\ numbc,' of ways of rep,-escnl in./..(

dipmeter resul ts is available e ..l.(

information used to determine the

al t itudc of the bedclin.l.( planes.

Dipmetcr logs have ;1 variety 01'

applications. Compu 1cd dipl11et er

results can be used to determine (i) the

gross geologic struet.ur<ll JCillllr('.c;

crossed by the well bore (iii

sedimentary deta i ls with simd bodies

(iii) t.he depositional environments. ;Ind

(iv)sl rn l igraph ie am i vertic;lI

(Itieknesscs.

64

-+ Tad pole or arrow plots lFi,/..(. 5.8(a) I

-+ SODA (Separation of Dip ancl

Azimith) plots-+ Listings

-+ Azimuth frequency plols

-+ Histograms,

-+ Polar plots,

-+ Stick plots, and

-+ Stratigraphic plols

N.B. Other factors that a ffec t w ire line

log signals include the distr ibution or

shales ( laminated. nodular, or cliperscd).M(';lSurements are also allecleel hv

l)orcllOle conditions, especially washoll ts

1'01' (he I leutron porosily tool and (11('

0= ( I / I / I - f "where R, '= R " , q ) - " ' S , ~ "



66

where:

1'",,, = rock malrix density (assullle

2.65gll1/cc for sand)

I,. '= bulk density as measured

by th e tool

I , '= fluid density in th e invaded

ZOne (assume 1.0 gm/cc).

N.B. In ga s bearin,£( sands. make a '

qUick correction for t he gas effect on th e

density Jog by reading a densi ty value,

approXimately ;.. across the FDC-CNL3 .

sepami ion distance.

07'

I' '/1(1 - / ,

(b) Caculation of the waterresistivity (R'£l

Determine th e value of formation water

resistivity (Rw) in the water bea ring

sands from th e calculated porosity and

the resistivity log using Archie formula

simplified for S" '= 1.0 ie.N =R

II / I fIwhere

1\, '= resistivity of the fonnaUon water.l ~ , . = resistivity of kno\vn water bearing

rock (use the deep reading LLD C'lIJ'VI'j

Qualitative and Quantit ative

Evaluation of wel l data

Qualitative Quick look

Evaluation ..

Use your knowledge of log response in

a sandstone/shale environment. and

establish the folJowing:-

(i) the locat ion of the reservoir sand

zones.

(ii) th e location of the shale zones.(iii) th e primary fluid contacts . and

(iv) th e primary fluid contents (gas.oil and water) for th e reservoir sand zones.

In = cementation faclor (Llssume 2.0) andn = Saturation exponenl[LlgLlin assume 2.0)R, = Resistivity measured by til(' LOt;,l1ing TnoJR" = Resistivity of the formation hrine!wale,-

resistivity

3.16.2 Quantitative Quick Look

Evaluation.

(a) Calculation of porosity (0 )

Calculate a typical average

porosity in the sand containingeach fluid type using th e formula:

3.16

3.16.1

...

0= porosity calculated in the water CHAPTER FOUR



zone (in fraclions)111 = cementation faclor (assume 2.0 in

this case).WELL PLANNING AND PROPOSAL

(A SUMMARY)

Note: Use the a v c l - a . ~ e valuc of the

formation water resislivities found

for the vanous water zones.

4. I RELATIONSHIP BETWEEN PILOT

HOLE AND DEVELOPMENTWELL:

Calculation of water saturation (Sw)

69

i. Pilot Hole: (Remember --7 An Exploratory

Hole).

1. Well/ Hole drilled for gUidance.2. Essentially of geological input

and interest.

3. Basically to appraise the objectivesand/garget aimed at understanding

properly the nuid contacts, structure,

and lateral extent of the hydrocarbon

column. and

4. Dl'ilIed vertically.

BEFORE

ii. Development well: (Remember --7 Drilledin order to extract the available

Hydrocarbon in that field).

1. Can be vertical. deviated or horizontal

(Conventional)

2. Drill vert ical ly to target. and then.cement back (bottom to depth frolllwhen you now deviated) in order II I

•

68

1\\kc one average value for R, foreach zone.

Determine th e R, value that wouldrepresent each zone best.

where

R, = resistivity of hydrocarban bearing

formation (again use (he LLD)

R = formation water rcsistivitvw

(assullled ('ons(;l11l <1S e<1 I('u 18lerl above)

0= porosity re-caleulaled in the

<Ippropriatc Z011e

n = sa(\lrntion exponent (again assume

.0 In IlJis case).

Using the porosities an d calculated

abovc. thc' water saturation in th e

hydrocarbon bearing zones can be

calculated with Archie fOl-mula

RS =(-"-)"" /) III

\, v'

Note:

(I l(I I)

(cl

. !

achieve th e desir'ed tmjectory/welJ

I

INB . DPR stipulatets rnll11llllJIlJ ( l I s t a n c ~



r .

.'

path

3. Essentially for Reservoir Engineers.Well Engineers (driJlers) working incollabomtion with geologists.

4. 2 EIA (Environmental Impact

Assessment)

Thl': following Environmental issues

Illllst be considered when planning andproposing a well:

1. Water/River pollution

2. Air pollution (flares. exhaust emissions)3 . Noise pollution

4. Impact on inland water ways (marinetraffic

5. Solid/Domestic waste proposal

.6. Managing dredging spoils7. Emuent quality monitoring

Plus '

LARS (Location Area Reports)

4.3 RESERVOIR MANAGEMENT

Mllst consider the follOWing factors:-

I. r·'ltlfd contracts

2. Drainage distance, distribution andin ted'erence

3. Reselvcs to develop.

70

between producing wells from r1 rnwrvoiI'to be 800m. Cotlld be less blli Ihisrequest/change mbt be backed Lip willifacts and appropri4te permission.

4.3.1 EVIDENCE OF JUXTAPOSITION OR

COMMUNICATIbN OR NON-SEALING

BETWEEN Twd SAND UNITS.

1. Same original I 1 U i ~ contacts (values)obtained from Sary.d files

2. Intervening shale is not sealing

3. GST results for present fluid contacts

or RST I

4.4 ADVANTAGES q F HORIZONTAL

WELLS OVER VERTICAL ONES

1. Less problem of draw down

2. Penetration ratr is more gradual3. Negative poroSitY eflect is Reduced

4. Marc hydrocarqon

5. Reduced ElA prpblems

6. Vfore coverage qf the proposedhydrocarbon reservoir. ,

7. Though expensive. the over-all cost

is eventua lIy chf8 per.

I.f) USEFUL TERMS IN DISCUSSING

RESERVOIRSII

(Vis-a.-vis Well Plaqning & Proposal)

III

71 IIII

.. 'INB:

4.5.1 (i) Drilling:



. "

(1) - (5) - 7 Vertical w e l l ~ ..

GUT -7 Gas Up'to_

GOT ~ Gas Downto

OPT -7 Oil Down to

0UT -7 Oil Up to"GOC -7 Gas-ail-contact

owe -7 Oil-Water-contact

WUT ~ Water Up'to

73

1.6 TERMINAL DEPTHS (TD)VERTICAL WELL, DEVIATED WELL

AND DEVIATED iDATA

4.5.3 UP-TO & DOWN-TO

The realjactual fluid contact but not

yet seen in the well. E.g. oil-up-to -7 oil

occurs to lhe topmost part of the sandbefore the shale above it.Pil-down.,.to -7 oil occurs To-the bottom

60st part .of the sand before the' shale

below it. Table 4.1 Shows examples

from CPS-3.

," I (, i' IJ: .. , r

(2)

72

• Best done at the c rest and no t at th eflanks (un le s fluid conta t a r e

obvious)

(ii) Types of wells

a) Exploration/Exploratory -7 Pilot/testwell. . . , l : · ' ....

bJAppraisal -t Actual hydrocarbon I

column detennined.c) Development ~ recovery of the

hYdrocarb9ll aVailable.

( I)

Fi'g.4.1 .Ulustratton shOWing different fluid contaot .

E08= End of Build4.6.1 (Al . VERTICAL WELL



Bull.1 'I ..... IW.f1

- ,- -

I II I

I IA)\ I n c l i n ~ t i o l lI ' ' ' 'II

TVpBDFI

I i " '- FlnhIIIII

j - - - - - - b - - - - - ~ ~ ~ - - - - - - - - - - - = ~ l D

VerlicOl \ Secllon MII(lrinmtal di"pl;h.cnwnt

75

TD (along hole - flah) = DF'E + (a+b) whcr('DFE = Denick Floor Elevation and

(a+b) is the well trajectory.

Fig. 4.3(a) Illustration showing the estimat iOIl of

TO fo r a deviated well.

Note:

i. At th e Landing point (Heel). the drilling

continues at th e ma,'Cimum inclination

(tangent section) until th e TO is reached.

ii. As much as it is possible to determine

th e Vertical Section and the Tangent

section. i t is not easy to do same for the

Build -up secLion since the build up

angle rate is not constant .

4.6.3 (el DEVIATION DATA (Drilling Engineers)

1'1/0(. 4.3(b) Illustration showi.ng basic deviaLion df l i l l

JV!)';o.; I \ I \ I ) I H ~ I 1)1 1

,\ }

U•"rrl,h.l'lnil,

DH D·rr;I"'llt'lIlI.lI'I,llipnn1 1 . , l u l ~ ; ' : hult'l .... r \ , l ) B [ ) ! ~tl.'l,,1 \,·r!'I.lll)"llth t',WI

IJ\'rn, h I" .. ,r'

\,lll'!'I'IVDS:-: L11".,llltll' ,.1 ;"

r [) "lib ",',I

r - " I . t " " ' ~ " , . K I ·~

x

1

\lntll.:.,1 "I('CIItHl

'tlMI,·'Ullild

"01'

/ f - - - - ~ " ; - - - - - - - ; r - - - - _10 6 t t "' ,.,.

Lmdlll).; ' ~ I m l r . I l 1 J - : ~ ...1 ... ·.-1'''11

(ht't.'lt

- h ./

74

C::r-ti: D e n ' l < ' ~ FI

J' i I '"

J

=1 j Cround ~ l l r l. . .kl '

r v D S ~ '

IFt"1Tn

Pig. 4.2 Illustration showing TVD fot, vertical well

4.6.2 (El DEVIATED WELL

S. '" dnli111 ...v=-- /



Flail

Tall'!' = drijiTVDBDF

CJ" driji

(),\o.v =--F/{{II

... TVDBDF = {!J'i/i

T{/II<!'... TVDSS =TVDBDF - DFE

Other deviation data include:

• D e p ~ h of target

• Horizontal displacement/vertical

• section/drift to target

• Build up rate

• DFE

• Maximum Deviation

• Azimuth (Direction)

• Inclination or Hole angle (</».

4.6.4 Drift

Diagmm (Vert ical ity is very important

and should be maintained as much aspossible.)

I II I III h.l!l!,

l"tt,

i ! -- OrifJ

76

DEVELOPMENT OF RESERVES

• Production Engineers

• Can be thmugh

(iJ Water injection.(ii) Gas injection. or

(iii) Gas liftThe objective: drive/increase the aquifer

pressure and move the oil (strong water

drive/strong acquifer support and this iscommon in th e Niger Delta (DriveMechanism)

Result - Improve recovery/productivity.

N.D. Weak Aquiler drive ---7 Recovery isnever 100%.

4.8 SIDE TRACKS

i. What is a side-track?

Answer:Drill ing a well from an already

existing one. Reason: possibly abandoned

[or some genuine reasons.

• F'or example. a horizontal side-track isdrilling a horizontal hole from an

existing well into the reservoir wherthe oil is collected. You can also have

vertical side-track or deviated sidc'

track depending on the circumstan '(. )

77



z

Sl

... ... ... ... ... ... ... ... ... ... ... Ii0 0 0 0 0 0? '" § '"

.... '" .... .... '" "... g ...'" §

..... .'" '"

In S 0

'"

;;:n.. .... ... ..... '" ...

" ~ F . !"... .... .... .... "... .... .... .... .... .... .... .... .... .... .... n - '1('" ... '" i w

:§ ll:

*6! g: :1'" '"

.... !:::::::; ", en w :a0 N

'" '" '" '"N .... W

" ;j5DII

130

"... ,:. II Z l . ~.. ....h :8 :80 0 0 0 s f:

0 §uN 8 N0 ... ... '" g:.. .... ...

'"0' '" ..... '" '" '"

..... .....

II p-I, , ,, "... ...

51 § :5 - II i l . ~0 0 130 0 s S II

'"... w w r:; N

:e '"... 00 w l!l :c II... w co ... .... .... ...

l-N G'l"

"VI !'• '0

§ .h § :8,:..91<'

0 0"00 "6'.... N In

C> 0 C> ...'" 0 co ... C> C> C> C> co

I: 6;'t:J§ "0. 0

S S"O '" 0 0"0 0 0 0 0 0 '" 0 0 0 0 00

" Q". ,' " .! '... ... II C:N

0..

"0 s s s 0 0 0 0 OnS....

t::i t8 2 :0 '" ::0 II

'"00

'"0

0 '"0 N 0' 0 N 0 N 0

'"1-

" 0... ,:. :: 6:;>

0 S II g0 0"

0 0 0 0 0 0 0 0 0 0 0 0 0 0 w

•"II t,:.

:5II

0 ::; ... :;o

0 0 0 0

t :::! w w W '" :: '"0 <;; ;;; 0 0'"w 0 0 0 0

'"

" l§

N:0 '" 15

... r..... \II W .....

'"... :g ....

0 00 0 ...

'"

0

'" '"

0 00 0

'" ""

8 fi w ... ... II

:l!...

t;; N0 0

:;:j II0 , 0 In N 0 ..

"IIII8"I

";. ::;; .. - ::: ..oD 0> .... '" '"

... w ..... II... .... 0

i& - L A ~ ~ I 0;

IIII

'" g; 8l 8l 2l '" g; g; g;1I'"

00

'"

2: Z

o 1.0

= '"I

z Z'o 10Ul CIl

6 ) f ~ B J lll+ 8JB lBqM on1',' [HjlIO'l,!J q JO

(JO:pBJ AI A O J 8 ~ ) dH

[Xl8AOJ8J 8 ~ B U I r l l n ] ClD = dIlOJ.,S •

8JBId U1 ATI"Brll1.h no ) f U B ~ } { J O ~ S •

I:iIIO-LS

I dIIOLS I '6 °

ONI'I'IIHG 'lVSOdOHd

'ONImIVId ' I ' Ih NI 03S11S W H ~ J , ID\IOS .!IO ~ O I J , I N I . i l ~ O 6"17

0 ( S 8 ~ S B M . UJIIPb) 1JBdUl!

I B ~ U 8 U I U O J 1 A U 8 sS8I ~ iU8WUO.IJAU3 (p

S ~ d S S B ~ d n ~ r x 8 8lfl~ U 1 Z J i l l q d o ~ 1 U 8 W 8 . o B L f W -l8S V (J

"uoqJnpo.Id P d ~ B . l 18 JV "N

on d 91 » l lMOP MjlP .ldM.0'1 On!

°.101 BJ

iU8Ul8A0.1dUlJ AlJAJ1Jnpqld

818qM (9L -dId) AlJA!1JnpOfd J8H8H on.°8Ioq UJB.Ip rBiuOZ110H OJ

'SiY8udq u9H npoJd (q

jp;;>.I1nb8.IliOQJ8 8I0L{ ~ i B T P ; ; > W J d ~ q ! / d o l oN "n

u qBJol M.8U JO UOnTstnbJB oN OJ

°fU8f q oJ (B

: . l3mSUV

= Initial oil Ion alion v 1 1111 fa r

E, = Gas expan ion -[ ct rOR



Up Ihll1l1'11 ,,,1<- (1111'1'" 1'''';,lbl,,)

/

, tl\l 'll thl'O\l'1l

~ I d c /unrL'lJ.ih'l')

'-/1-"-./1. 'J ' - J ' - . - __<j_. _.

!

F = Net-to-Gros ratio or fra lion

of the total sand volum Ib'lt i.considered to be poro'll

4.9.5 Ultin1ate Recovery (UR)

DR = STOUP

RF(See 4.9. Labove)

4.9.6 Mapping Across Faults

• Use the Upthrown side (more reliable)

• Down thrown side is unreliable.

Fig:.4.4 MapPing across Faults with referenceto th e throw.

4.9.7 Well Numbering

\VeU Numbering

E.er UVLW/-l

Real well name bas ed on gridrl

= first wrell but if 2. for exampl

it implies econd well with th e fir t

already existing in that field.

8180

• Unit measurement for oil

• Stock tank barrel

4.9.4 Scf

4.9.2 mmscf

Unit of measurement for gas

• Million standard cubic feet

4.9.3Stb

xFx¢x(J - S"'r

• Unitmeasurement for gas• Standard e'ubic f ~ e t . II: ..); ; # · f \ ' , ' j t. 1 I t INote; (Compare 4.9:.4 and 4.9.2)

4. 9 . . 4 ! ( ~ J 1 .1 ' ~ t n t t u n 1 I 1 g I g ~ ~ ~ ' t V § I :. c' ir- I ',; '" lJlt"( ' j . ' 1 '11/

Remaini ng r eserve ---7 undeveloped

reserve or Developable reserve minus (-)

Net production from existing wells.

4.9.4(b) FGIIP

Free Gas iniUally in place.FGIIP = VI'. x F x <p x(l-SIV)xE,

V l! = Gross bulk volume ([romgeological map).

<p.= Porosity from (Petrophysics)IV<'- Conate water saturation

(P lrophysicsJ

II

4.9.10 Oil Clolwnn -4 Acceplable/4.9.8 Naming a field



Commercial interest

• 30ft; depending on drilling style andsuch petropbysical features as:

• porosity, I• permeability,

• saturation I

• lateral e A 1 : e I 1 , ~I

NB: The petrojJhysical features should

account for reservoir properties Vis-avis sand qualit)1.

4.9.11 Reservoir Dtive Mechanism:

i. Dissolved g a ~ ,ii. Water, Iiii. Gas cap, or I

iv. A c o m b i n a t i ~ n drive.4.9.12 Scales (maps land X-sections) - 7

Standard: setiTemplates)

• Most horiZ?,ll maps - 4 1.25,000

• Most X - s e c ~ i o l l acrossconventiollfl wells (deViated orvertical. -4 t 10,000 or 1:5000

• For horiZOlltal weIls,

• Vertical sCClfe -7 .1: 1000• Horizntal s9ale -4 1:5000

I

II

83

III

AZ -+F:l

..l l l l ~ "Ell -+ Nnl'lhlll.\;'<

1 -+ Fi"'l \\(']1 In til_ I,,· ,jI' I I

! l ul l I ",

". -

--

r -__2..'uh

IUIUI ,h , ~ ! o 'I"'!.""'''/

,/

A

Fig: 4.6 In fl l l Faull

82

[I IB-+ AZE8·1

i'il(, ,1.5 Nanling a field ( " ' ~ I\ZEll-l

tNnrthlll';":

,

• Use grid name; not n u m b e r ~• Use co-ordinates-Eastings and Northin,e;s

Note:

El.O and E3.0 are key faults. while

E2.0 is an in fill fault.

4.9.9 Interpolation (In fill)

4.9.13 Dog Leg Severity:i. With very low permeability,

ji That produce flnes which could



High Dog

leg ~ e ~ l ' f i t y ,{ : Wl,ll p,llh.Wl'llp.Hh

reduce vertical penneabilily and

impair production, and

iii. Can act as baffles to vertical now.

NB: (i). (U) and (iii) definitely impair

production.

85

What are Compartmentalization

and Homogeneity of reservoirs?

Answer: Location (Land)

Answer:

il Compartmen1illization -4 Pault.blocks/compart.ments

ii) Homogeneity ---? Almost

homogeneous: Wells in the

reservoir ar e in communication.

4.9.17

4.9.18 EOR& GOR

ERO ---? Enhanced oil recoveryGOR ---? Gas oil ratio

4.9.19 What is Ullage? Or (space)

Answer: Plow station capacity: say 40.000 6pdE.g. gross liqUid ---? 6pd (barTe! pe r day)

Net oit ---? 60 pd (barrel oil pe r day)

-1.9.20 What is Cellar?

Fig: 4.7 Dog Leg severity

Answer:

Shales

4.9.14 Draw downs (measured in psi):

Down-down simply means waler

encroachment or water break through

i) Conventional well (vertical & devialed) ---?

fast water encroachmenl higher drawdown

ii) Horizontal wells ---? slow water break

through. and therefore lower draw-down(can' be managed).

4.9.15 Why do you inject water into wells?

Answer: Either for pressure maintenance

or roi- disposal into shallow

aquifers.

84

4.9.16 What are Heterolithics or

Heterolithic layers?

Circle and Cylinder Tol r' n 'i.

1

4.10 TOLEAANCE

What is it ?



1I

(6)

•IJ

I -,I'I"" . ~ .. _..•(/\) I 5'

A=Cir" Tolc'rallce B = ylinderToleran e s

Fig. 4.9 Cir I and Cylinder Tolerance

87

• N w Technology

• Increase productivity e.g. horizontalw 11 have longer complete intervals

and there10re better oil recover (e.g.Att ic oil)

• Can be used in built up areas.

• Optimal penetration of reservoir

• EnVironmental preservation (Ie snumber of wells)

4.11 WHY DEVIATE

NB: The oil accumulates behind th e fault

as expected. Therefor . dr il l there and not

across th e fault (fault scoopersl

"

Reservoir

I

86

Fl . 4.8 Square box Tolerance

Allowable l imit (about 25 ' away from

OWC but within th e reservoir.

owe

Permissible limit on eithe- ofhorizontal section/path. ..~ r n p rp box. circle or cylfnder

i. Square Box Tolerance;

Horizontal Section

"

NB:



• Production from 2 more reservoirs

usin th e same tUbing (or string)

• at allowed by NNPC.

• Nonnally 2 strings (short an dlong) are used

But there is a prob! i l l ' see questionbelow:-

89

•When a well is drilled close tq a fault.it is placed at least 100111 way t

account for uncertainty in IIIpositioning. Surely some atti oi l I

left between lh e well and fault.

How substantia:! the attic accumulationWill be . depends on th e shape of thstructure.

i. How do you account for th e production?

Le. with the drainage point (perforation

a indicat d the production is col lec tiv .

4.13 COMMINGLE

1) What is it about?Answer:

8

4.12UNDRAINED OIL (Attic oil) (Fig. 4.12)

i. Background:

• I t is becoming i n ~ r e . a s i n g l y costly andmore difficult to find new oil.

• U'ndrained oil n eds to b tapped.

• UndrainedaU

i an accmulati nwhich cannot b drained by th

exi ting drainage at a par ti u la r

time due to Some constraint .

ii. Classification of undrained oil (onbasis of occurrence)

• Attic accumulations

• StartigraphicaJl by pass d oil

• Trun bedded intervals

• Small accumulations

• Low reservoir energy accumulations.

• Accumulations

() -VI, lkJ I \dl

(I',llIlt <'((1°1"''')

F i . ~ . 4.10 hHlIt .' 'oop'r (D viA.l dwell)

4.15 TIP ON THE PRODUCTION OF

X-SECTIONS FROM TOP



91

STRUCTURE/HORIZON MAPS

o Geological Template for the X-sectionuseful in th e control of scales (Vertical& Horizontal) -,

o Choose appr(}priate Scales:• Vertical scale --tis vis-a.-vis the

Template

.. Horizontal Bcale -7 nOImally providedbut select w-r'lich can be

accoffirnodated in your final section.(Use th e V ~ · r n i e r ) .

'-"'.'J vertiCal._:.scale -7 startwith th e lowystt4.la..-;'. Canton ..

a Respect al l faults. centaurs and wellswhict, your section Jlasses in the block.

'0'''' Nu;m] :,er of c o n t o u r ~ ~ . between 2imIDedfate control ~ j . o i n t s isappn.;dmately

:::: .Difference in e l ~ ~ v a t i c ~ n (tops}Contour : n t e r n ~ t l

This value m u ~ r be a whole

number (i.E' nct.

a fral:tion).

Fig. 4.11 Commingl

• Required after well proposal

• Involves appraisal of seismic data i-a-vis Well proposal

• Check co-ordina tes of the drill points

proposed

• Check on amplitJude maps and seismic

sectj,on, (DHIS) I where DHIS means

DirectHydrocarbon I n d i c a t o r ~ ..

• See how the de-ta from th e anlplitude

maps relate to ' ~ h e faults, Confinn any

closures ..

• Relate this infr)ffilation Lo the finaldepth Inaps of th e objective level with

contou:s using Lhe actual fluidontacts as prop.:>sed [rOll1 th e log data.

4.14 SEISMIC SUPPORT

CHAPTER FIVE



(2)

_I

TO- . 1hlni' l l l l l . l I : - " ~ t l l l '

f

I'

"

~ HORIZONTAL SCALEFig 5.1 Construction of structural and

Sedimentological section.

QUESTIONS AND ANSWERS USEFUL IN

WELL PLANNING. PROPOSAL AND

DRILLING

93

1,2 ~ drilled wells: Pw ~ proposed well

TD '" Terminal depth within the Objectivesand/Target

oF· ~ Symbol means additional depthinformation no t accommodated in thesection.

5. ] Why do you construct Structural &

Sedimentological Sections?

•

o·ui' t

f'I

.!'lL

92

i'M,

;f1!nswer: -;.'!, __ i a 1 ! t ~ i J :in order to~ h o w , a t € ~ I " i . ; S ~ ' ¢ a l r e a d y drilled Vis-a 5.3' In th e Hbrizori<map ~ why are some

wen p ~ o p o s e d and d r i 1 1 ~ d within the



,. :iVis the, 'tW'Q · ; w : e l l ~ ; · : ~ ~ f X J fN:>w far you :havegone q i r e ~ l.·e:. 'the,weU ..has been drilledfrom the sittfaee.i ;I \ '. :

5.2\ Pr.ojeclion af'wetl ' 1 . : . J t - i l e : c ~ i a n along'strike - How d O J l ~ ' " t . ,i . ,; :" ,

o......... Producing well (control)

+-- Projection to section

Line of se tion

Proposed well

Fig. 5.2'Well projection with reference to th .line of section.

Answer.: I Put a r u l ~ r : parallel to lit);e ofsection and· with _a setsquare placed

perpendicular to ·tt. measure the

projection d i ~ t a n c e : and read of f the. scale

and calculate the result. This is the

projected distance for tl:1e p r o ~ u C i n g wellunto the line of section.

94

boundary fault?

Answer:

Check the sand file. and you will see thatthe fault did not penetrate' the objective

zone.Also check if

completelyfaulted (eF)

or partly faulted ou t (PF) is the situation.

5.4 What is the Basis for any cluster?

Answer.The main aim is increase inUltimate Recovery and there must beoptional productivity.

The gUides are:

I

• Structure; . e ~ e r V o i r management.

• Fluid contacts (away frOID' gas avf<twater (safe distance}.

·f I' r. ,. I

• D . n . l i p a g ~ 9 J s . t ~ u c ~ . h ; f i ~ t r i b ; u t i o n , '(there should.be n Q . i l l t e r f ~ I : ' e p c e J n o ttoo close wells).

I ,

• There must be r:eserves to develop.

95

5.5 WIt t t e Basis r any cluster;?,.Co:ntd.x y Z f

(b) In horizon map -1 OWC/GOC

(original) are or-en us d unless



there ar e updates. The v lu an

be obtained fron1 the Sand fil ( ).

+-1-- Cluc,kr 'x \\ "II - Ipr0posed

I'rodlllil1g \\Ie III~ \ " 1 t f ( l l l i l 1 g well

- - - .....-- roweFl,n Oil

(Ilelcrolithic inlr,l-

SI iA LE r<'servo;r shnl '/L'nfflc)

_ .!!,(l c".=:... __+-- OGoc

I (I Oil/Gi\S- - - - - - - -+- - I 'GOC

FlO Oil/IV,ller

n n n I IT IT I ITITIT -+-- )OW(

97

O"plh

(iI1Cr(','$e)

Fl.O is the target/objective reServoir sand.

, 'Pig.'S.4 Fi4id contacts "

N.B.: In the above diagram, th original

gas /oil contact has dropped to PGOC(deeper) while original OWC came up

shallow to powe. Th refore, oil column

is reduced while th e gas column

increased. 'T ~ ~ ~ e ' .

,wd!caUeJ theneed/encouragement: ' t@f qrtU ~proposed Well-I,., . , " J -ok

96

A n s ~ ' .J ; P ~ ~ ~ ¢ n t .-;: saturation'tools are usecj'

RST (less. ~ p . e n s i v e wireline tubing,

GST (Rig; mGre e x p ~ n s i v e ) , and

Material Balance calculations

N.6 x, y, z , F, are proposed wells in tbe c J l 1 ~ t e r .,Ad

Fig. 5.3 Cluster

N.B, x,y,z,f .are proposed wells in c 1 u ~ t ~ r , " A ".Cellar -4 Land LocatJ,tm I ' •

.Slot -4 SW8mp..u>cation.. "

N .B.: Cluster is very good for offshor

drilling operations. So many wells can be

drilled from one spot.

5.5: Distinguish between the original and

present fluid contacts; what are

their implications?

Gamma Ray Logs for the structural!sedimentological cross-section:

a .5.H".' ..6 What is BS:$: W?

Answer: ca,lled Basjc Sediment and Water



99

Single completion -7 1 ' s a h d / i r i t e ~ lD ~ a l '

completion -) 2 sands/intervalsstrings (1 s}iort and 1 l<!>hg), and'

Multiple completion-7 2Q r 3 -moresands/inteIVals. .-

Answer: Reservoir Management.

TVD not FTAH. Why?

Answer: The Cross-section ha s to be in

1VD so that we work on the correctthickness of the reservoir.

Note; +/-65ft; +/-50ft e.g as seen on

structural/sedimento-logtea-r·cross-section.Why?

Answer: These aTe r a n g ~ s of.'uncertainties of depllis that shOUld be

so indicated on the cross-section.' .

5.10 What ar e single, dual and multiple

completions.

5.11 Choice of drainage area: Horizontal

well range; 1,OOOft- 1.500ft. Why?

98

or simplywater production.

5.7 What is t he l east separation distance

between 2 -wells (allowable in a given

reservoir? I.e proximity to other wells

from the planned/proposed one!

Answer. Producing wells from areservoir have statuary approvedrequirement by DPR (Department of

Petroleum Resources) of 800m unless

otherwise discussed and approved!Adequate data must J : : > ~ available.

-- -- -' I· -. -- - - ,

5.B-Define tbe:- following t.erms i t s u ~ l 1 yseen in th e Drillers planning reports.

-7TFO -7 Tool face orientation (bit)--+Turn -4 R ~ l a . t e mbre to direction ( A z i m u t h ~ !-7 Build ~ Relates mar La inclination

-7 DLS-7Dog leg severity (approximately

equal to build up rate)

-7 VS -7 V rtical se tion or drifL or

horizar tal d ispla ement .

N .B. Directional Drilling Engineers

(Good ones)

(i) Baker Hughes(ii) Anadrill

(iii) Petrodynarnfcs:

•:" __ Vl·I'I,•. 11X fleh



101

A.,... d;""

. "or

Build ul Drift

t .... , holt ..._ •

"'/ .

wn;!'I U n ~ I ' n ! /:"\.'\.-11«'1:,....-

.L.. ~ J r i n l ..... _ . . ''I'

Fig 5.6 Kick off point (KOPl an d

End of BUild (EOB).

Answer: Gas Saturation Tool which is a

Petrophysical instrument for pressuremeasurement.

N.B If the pressures from twowells/reservoirs are close or behaving

:tIikf'. i[ means there is interference i.ethere is communication.

Best eVidence of communication between

two wel ls is presSure data using RFT.

5.15 GST?

Y fl

L.,nding point (Ileel)

,.

-n- / TO

'/

5 )2

Fig. 5.5 HorIzontal well r a n ~ e

DFE: What is it?

Answer: Derrick Floor Elevation.

Determined during the well flx bysurveyo rs when the rig is brought tothe site.

5.13 What is deviation/build up rate?

How is the calculation done?

100

Answer: Done by well Engineers with

the co-ordinates (surface and

subsurlacel supplied by th e geologists.Build up rate can be

• Close co-ordinates (fast!. or

• Too far (slow).

5.14 KOP and EOB?

Answer: KOP ~ Kick off point

EOB ~ End of Build

Done by well Engineers during theirprogram calculations.

NB: You do no t kick off from the

surface (usually) (see Fig. 4.3).

5.16 Seismic Support - Why?

Answer:

. (il Check seismic quality i.e check faults.

5.18 Collision Risk?

With respect to th e surrounding wells.



DHls, Amplitudes. nlld how the well is

planned.

(iii) As part of ( I l l ' seismic support,

always ensure' lhnl the horizontal

seclibn is fixed within the

objcCiivc/target.l81.0 sand).

Wl'1!

lr,ljL'C!III'\ 1'1

/)1'111 p.lth--+

SH.\LE

Hl !Ql . :;;';! , : ! . ! , , : : ' : , ~ : : ' ~ ' : '. ..... :....... , . : . ~ : : : i : : : ' : : ' ~ ; : " ~ ' · ; ,orL.lndlng , : ; . ~ ::'l ,1)',1 . ~ : : •• I.EJ.O SAND ·Il .......\ .. ,. , ~ ; ,Point : . : !.;. ': ;: J.:' .,' ...: :' 'I . i : . i ' ~ · : :: :,: ,;: :.: , ; , ; ' ~ ' . : . ~ : . : , : ' ,

: > : : ~ . ;/!UV .. : ; / y ~ y : · : ~ i : . ~ · : ; i ; L ~ ~ I / { ~ i : / . ~ \DFig. 5.7 Landing point (Heel) and Horizontalsection.

5.17 Shallow Hydrocarbons; implications?

Answer. If' seen -i > Problematic -i> blowout (if gas). Normally no t antiCipated i.e.not expected. But i f there is.cementation of the a nn ulu s must be

done in order to isolate these unwanted

Hydrocarbon zones.

102

these must no t be too close. (remember

th e DPR stal:utory requirement)

5.19 Overpressure problem?

(it Result -i> blow-out

(iiJ Remedv -i> mud sYstem (increase or- .reduce as appropriate)

5.20 What is the Problem o f shal es i n the

borehole stability?

Answer: Usually hard, fissile shale;

therefore use of pseudo-oil-base mud isrecommended for drilling. This problem

is related Lo overpressures and is

commonil l

shales. as some of them areexpandable or reactive (depending on

the mineralogy).

).21 Uncertainties?

Answer: can be due to

(i) Structure -i> dep th uncer ta in ty

especially where U1ere is

insufficient well control (± 30ft ispermissible)

(ii) Sedimentology (i.e sand developlllt'lll)

103

ll"-

(iii) Fluid contacts & types: original is

.no problem. But present can be

I

I

I5.24 What i s p lug back?

Answer: Aftbr drill ing. cement is



5.22. Name th e mud logging types

5.23

unknown/uncertain.

Therefore, . pilot hole is recommended

and drilled in order to reduce these

uncertainties.

Answer:

(il RFf ~ Repeat Formation Test for

Hydrocarbon pressure.

(ii) MWD ~ Measurement while

drilling (e.g deviation etc)

(iii) GR/CDR ~ Logs. which are not

the conventional wire-line logs

NB. The three (3) are done whiledrilling instead of the conventional

wire-line (clone after).

In the prognosis, what does 11569

ftss or 11580 ftss for example,

mean?

Answer: Estimate of the landing point(Forecast)

104

used as a pluk back. Do no t leave the

well open b e f o ~ e continuing to dri ll the

horizontal secdon.

5.25 What is I n C l i n ~ t i o n ?Answer: can IJe measured, planned,

MWD or Gyrg. These are deviations

and Log rne¥urements done whiledrilling But G ~ r o is done after drilling(wire linejuslCjs a deviation survey)

5.26 Name some wel l data for th e

objective sandi

Answer: I(i) Expected Top of sand (ftss/ftah)

(il) Expected Grassl Hydrocarbon column

(ft gas / oil) I(iii) Horizontal Displacement or drift (ft).

5.27 How do you detect thin reservoirs?

Answer: SUmm¥ilY, [or the problems/

difficulties and ~ o l u U o n s . see Fig. 5.8

for a possible a ~ p r o a c h .fl.28 What are f>andstone Reservoir

characteristics Itypical of th e principal

depositional enrironments?

Answer: See examples in Fig. 5.9 (a & b).

II

1?5II



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S H f . E 1 ~ ~ : : : : : s .p e : r . . c r ~ t Op L l J ~ 3 : e C i t a :m:..-( (rt1f'11 il'lllU;;reU:on

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me.>.: ~ ' X : l : I 1 ' ' ' ' . . t :~~ 1 . 0 ~ r · N m

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?:..- --'-_LLJ-Ll- - L -L -L . - ' - - _

o

THE AUTHOR



] 1

For th pa t tw ) ,ca :Ies, at least, rof.

Pius Ositadinma k 'k , ha remain a a

strong acad mic, nnd, pra lisi g ologi :. t in

the oil, gas co, I ,1n J VI .. l('\" upstr am sector.

P r e s ~ n t l y , h> is , full-l im' c nt\"act PIofe'sor

of Geolog n l l hl ' Imtl lJ • Lat U n i v e r s i ~ y of

Sciene and ,hnolog (Ii 1'), Enugu where

heteach II'. ' [nil w i n g ! ' l I b j ~ c t s : -(a) Expl r, lion drilling,

(b) ExpJ l 'i lt il ln , l' ( 1 It 'ics, and

(c) P lm l 'LIm 1, pi nlion Methods.

Prof. k 'k L ,) [,('llnw f lh G ological

Society of LonL!\)Il, and a Fellow of the

Nig0rian Minin > 'I gine and eoscientisl.

FU1'therm re, h '-ved lh nation (Nigeria) as

the Managing ir l)1" of the Nigerian Coal

C .rpOl'ali n, 1.1I1' of th arastatals in the

F dcral Mini. lr f Solid Mineralso wi pm nl (200 I 2003).

THE AUTHOR

For tile past two d ~ a d e s : at least, rof.

Pius Ositadinma. Okeke, has remaifte a



I ".strong academic, and a practising geologist'

tIlE! oil, gas coal and water upstream sector.

P r ~ ~ n t l y , he is a full-time contract ProfessOr

of G ~ o g y at the Enugu State Univ.ersit}r of

Science andT.echnology (ESUT),Enuguwhere

he teaches'the fa.llowing subjects:- i'(a) ' Explorationdrllling,

'-(b) ExploranonGeophysics, and' :

-"{£)." Petroleum ExplQ'ratiCljl Metho.ds. ,, -

Prof. Okel<e is a Fel low of the Geological'

Society of L I don, and a Fellow of the

Nigerian Mining Engineersand G oscientist .

Furthermore, he s' l"ved the nation (Ni.g ria) as

the Managin Dir ctor of.the Nigerian Coal

I CorporatiOJ1, one of the parastatals in the

F d er al M in is tr y of Solid Mineral

D veJopment (2001 2003).

shell - well planning

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