3601-measurements of formation pressure from drilling data
TRANSCRIPT
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8/11/2019 3601-Measurements of Formation Pressure From Drilling Data.
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o?
P.IME
TliiS
IS A P?eHF3XT--- SUEJWT TO CO.RRXTION
Bill Rehm and
4 mer ican In st it ut e
of Forf f l ati m Pressure f rom
i l ri i l i ng Data
w
Ray McClendon,MembersAIME, Dresser-SWACO
@ Copyr igh t 1 9 71
of Mining Metallurgical and Petroleum Engineers. hic
This paper was preparedfor the ~th AnnualFall Meetingof the Societyof PetroleumEngineers
of AIME, to be held in Eew Orleans,La.,Oct. 3-6, 1971.
permissionto COpy is restrictedto an
abstractof not more than 300 words.
Illustrationsmay not be copied. The abst~actshouldcontain
conspicuousaclmowledgmentof where and by whom the paper is presented.
Publicationelsewhereafter
publicationin the JOURNALOF PETROLEUMTECHNOLOGYor the SOCIETYOF PETROLEUMENGR?ZERSJOURNiLis
t~~~~~ygranted~o~ requestto the Editorof the appropriatejound providedagreementtO give
-
prcpercreditis made.
Discussionofthis paper is invited.
Three copiesof any discussionshouldbe sentto the
Societyof ?
etroleumEngineersoffice. Sucn discussionmay be presentedat the abovemeetingand,
with the ~a?er,may be consideredfor publicationin one of the two SPE magazines.
ABSTRACT
tion.
A seriesof drLllingequationshave been
Sincevelocityis intimatelyrelatedto
proposedfor the measurementof formationpres-
rock density,the techniquesinvolvedin
sure. They appear to work well and are as
detemini.n
g pressurefrom velocityor density
accurateas log-derivedpressuretechniques.
shouldwork equallywell &th drillingrate
% fleit probablyis not possibleto develop one
insofar.as drilJingrate is relatedto d-asity
equationthat W work under W conditions?
or porosity.
one of the series shouldwork quitewell where
good dx5Jlxlg practices are used. Calculations
2.
The other drillingrate/pressurefacto
have been made US* these methods in dJ. major
involvedis the effectof differentialpressure
drilling=eas of the free world and accuracies
AS the differentialpressurebetweenthe
approaching0.2 lb/gsl have be=n attained.
wellboreand fonzationdecreases,drilhng rate
increases.
The increaseapproachesa hyperboli
INTRODUCTION
functionand often has an -inflectionoint at
about 500 psi overpressureagainstthe formatio
There are two reasons why adrfig/ (Fig. 1).
pressureequationshouldwork.
It may be noted that both phenomenawork i
1. The basic theom of abnormal.ressure
the samedirectionat the same time. Reduction
due to porosityor compactionindicatesthat as
in differentialpressuretends to come with the
the bit entersthe high pressurezone,the rock
entranceinto the overpressuredzone of greater
becomesmore porous and less dense than it was
porosityand botlnincreasethe drilliiigrate.
previously.
This has been provedby the methods
However,it appearsthat the differentialpree-
of detennini.n
pressuresfrom we~ logs, shale
sure phenomenonis the more sensitivefunction
densitiesand seism~cvelocities. The pficiple
of variationfrom normal was proposedby Hottman
I%eseobservationsled to the belief that
and Johnsonin 1965.12 They firmlyestablished not only was the determinationof overpressu.r
not only that variation from normal was an zones possible,but that it was possibleto
indicatorof high pressure,but that M@ pres-
detexmineformationpressuz-esfrom dx5Jlingrat
sure couldbe measured by the departureof the The main difficultyappearedto be resolvingth
velocityfrom what might be e~ected to be
sensitivitiesinvolvedin the drWLing rate
normalvelocityfor the depth under considera-
fmctiono
Referencesand illustrationsat end of paper.
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MEASURINGFORMATIONPRE
~sIc c~i~~
Some basic fieldhvestigations,shortly
terpublicationof the paper by Jordanand
rley14furthercorKinnedthat the basic d
ationwas en excellentindicatorof differen-
pressure
~tl-,15+
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~ 3601
BILL REHM and RAY McCLENDON
FTREH. IimZLOFI@YT
The difficultiesin keeptigdrillingand
mui iunctiansonstantduringdifferentialpres-
su7e calculationsin transitionzonesmake it
desirableto developan absolutepressurevalue.
As a resultof considerablefield work in
comparisonof the variousmethods,the d equa-
tion of Jordenand Shirleywas selectedas the
best possiblestartingpoint sincethe sensitiv-
ities and mechanicsappearedto be both accurate
and usable. Field correlationindicatedthat
the equationgave a ve~ reasonableappro=-
mation of differentialpressurebetweenthe
wellboreand fozmation.
It was postulatedthat if it was possible
to correctfor the effectof mud weight,the d
tem would then be an indicatorof formation
pressure. Ibis was attemptedon an empirical
basis on a number of differentmodels and
> :- A&. S.llmwirl
whirh g=y~ ~
resi i teu u uc ~ ~ u gt
excellentindicationof formationpressure.
dc~= %d, .0 **0****(4)
MW2
where dcs
= modifiede~onent ti general
drilfig equationto indicate
formationpressure
MWl
= noxmalmud weightgradientfor the
area
MN2 = equivalentcirculattigdensity or
mud weight in use
The plot of the dcs
l;te~ showeda Curve
that was similarto acousticlog shale plots ant
shaledensityplots (Fig.k).
THE SOLUTIONPIOT
Using the d and dcs terms,it is
possibleto plot two curvesthat relateto
differentialpressureand to fomation pressure
The comparisonof these two valuesprovidesa
valuabletool in dflli.ngrate/pressuresnalysi:
(Fig.5).
The similarityof the dcs and the shale
densityplotsled to the beliefthat a pressure
interpretationmight be made on the same depsr
ture from nozmdlbasis as on log plots.
The originalwork by Hottman and Johnson12
indicatedthat when dealingwith log~erived
values,the solutionof departurefrom normal v
pressuregradientwas a power functionclosely
approachingthe logarithmic.
This was further
redefinedby Combs (1967)in te~s of sh~e
arfllability. The discussionof shaledensity
by Boatman2definesthe same generalfunctioni
terms of shalebulk density.
3asedp~arily on the comparisonof the
acousticand the dc~
solutionfor departure
fromnormalvs pressuregradient,a term was
developedh the mode of the Combs work.
This was resolvedinto the following
expression.
Grad = mLog (Normal-Obsemed)+ B . (5)
w h ere Grad =
m=
Normal=
Observed=
B=
.
pressuregradient,psi/ft
slope constant
normal d
at depth for the dri1
tools i%olved
dcs at depth for driU tools in-
volved
offset
This was actuallyresolvedfor field use b
means of a standad overlayand plot paper (Fi
6).
When plottingon coordinategraph paper,
where 1 in. on the horizontalaxis is 0.5 dcs
units,the eq-uatioiiec.mes
Grad = .398Log (Normal-Obsened)+ .86
. . . . . ***** *.***
(54)
FIELDDATA COLLECTION
The collectionof accuraterig informatio
is the obviouskey to the accuratedeteminatio
of pressuresfrom drillingparameters. The
originalpremiseof the pressuresfrom driUing
rate projectwas that equipmemtto accurately
collectthe informationwas nekesssxyand woul
be designedas soon as the parameterswere
clearlyestablished. The equipmentwas desigd
and firstbecame availablein late 1969. The
personnelin the units were extensivelytraine
for the specificpurposeof pressuredetermina
tion and upon their enthusiasticeffortsreste
the successand
accuracyexperienced.
DriJ3ia
data was gatheredon over 90 wells throughout
the world ut~zing this equipmentand crews.
The collectionof the drillingdata has been
continuallyimprovedby e~erience and the int
ductionof newer and more rtiable eqyipment.
DATA COILEC~ONMETHOD
Whether the solutionto bottom-holepres-
sure is plottedby computeror by hand, the
variationsin the earth and the drilMng proce
must be taken into account. Iheimplest,yet
most importantcorrectionis for vtiations in
the foxmation. Since the equationsdo not tak
changesin lithologyinto account,a stand-
must be established. Shale is the most conven
ient standardbecauseit is relativelyeasy to
identifyand displaysthe greatestdegree of
compaction. It is also the standamiestablis
by earlierwork in pressuredetermination.
Other standards,suchas silts,redb+s, or
sands,may be used but they are proportionate
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MEASURINGFORM4TIONPRESS~ FROM DRIIJZNGDATA
SPE 3601
I
:erto fiterpret.
In Gulf Coast-typearil.ltigthe difference
tt~eens~~ ad sh~e shows Up dramaticallyti
e drilltigrate.
The sand values can then be
noredon a
by tispection
1basis or CSIICeUSd
t oya dead beat band in the electronic
Tinisshouldbe spi checkedby
e anelysis.
In older formations,it is oftendifficult
vefi+y the establishedstandardsolelyby
ctionof drillang rate.
In these cases a
nationof drillm
g rate and sample analysis
y be
used There
is everyindicationthat
riationin torqueand rotarybounce can be
ed to definemore closelythe formation.
How-
er, it is easierand more accurateto use
mpleanalysiswhen using a mannedunit.
~afi~~g causes a major shtit in the pres-
re plot if it is not recognizedby a combi-
tion of sampleanalysisand an abruptoffset
the slope of the plot. Unfortunately,many
ultsoccur withinthe transitionzone where
th the lithologyand slopeof the plot are
=EQeA-A
~q~~&.~ s knwl due nf tb.~
u ...........---
ology of the area are some
this case.
The rate of penetration
llectedon a footagebasis
of the best guides
appearsto be best
(withfixed footage
d variabletime). Fixedtime and variable
otageincrementswere tried,but for some
ason,were not satisfactory. -m ~ener~, ~~
s been found that for any drillingrate up to
out 60 ft/hr a l-ft stsndti isquite satis-
At very low drillingrates, a standardof
ss than 1 ft appearsto rellectthe autc+
tic drillerratherthan the fomation. At
n? ~~ ft,lh-vf~ot.ag~
5Z2ingrates h excess..
andardof 10 ft appearsto be satisfactory.
e footageintervalmust be enoughto reflect
e formationratherthan the driller,but
ort enoughto showvariationsin the fomna-
Rot
ary sDe@
Rot~ speed is measuredby en impulse
vice, and rate is calculatedand reportedas ~
mericalvalue in rpm.
Eit WeiRht
Good snort-titenal averagesof bit weight
essentialto accuratesolutions.
The best
sults come as a
result
of the following. The
t weight is definedas the differencebet~eer
+l~+ngweight and stringweight when rotating
and pumping just off bottom and is automat-
ically calculatedand reportedin thousa??ds
f
pounds. A movitigaverage,
or
thifi-otier
electronicfilteris used betweenthe transduces
on the hook load diaphragmand the nook load
value end displayto dampen the bounce in the
drilling
assembly.
IW4JORCHANGESIN CONDITIONS
With presemtdrK1.i.ngtechnologythe casing
point is in the transitionzone. With the
settingof casingcomes a major change in the
values for the pressuredeterminationequation.
The bit sizeis changed,oftenthe mud weight
and mud characteristicsare changed,causinga
change in the differentialpressurerelation-
ship.
The changein bit size is correctedin the
ofig~~ lid ?
quation
where there is proVisioKI
for bit diameter. The changein bit type is
not
so
straightforward.On an empiricalbasis, it
was discoveredthat correctionin bit type or
correctionfrom mill tooth to carbidebits can
be made on a basis of bit tooth area in contact
w+.h ~h~ f~~_~~iQn,
..- ..
Then tM3 correctiontakes
the place of the bit diameter. So the bit
diameterencompassesbit type end is made.by a
proportionatecorrectionfor bit diameteras a
functionof bit tooth area in contactwith
formation. This, from a review of the etist~
literature,seemsto be a rationalcorrection
and may not be enttielyempirical.
The correctionto diammd bits is somewhat
3.
ma. -.-1 L 1 . . . a.-.
more axzx~cu~ and
to a AKSG u=6A=e As r.ct
been successful. When using diamondbits a
smell.sectionof hole must be dfled and the
correctionsput in by obsenation.
Changesin the drill stringcan cause some
difficulty,particularlywith additionof a
radicallydifferentstabilizer
assembly. This
may be aermlmt.~ f~~ s_@Q SS
change in the
--------
effect of bit weight,but it is difficultto
correct on any mathematicalbasis.
Again the
best solutionin this case is an additional100
ft of hole to establisha new trend pattern.
Changesin drillingmud propertiesalways
affectpressuredeterminationto some degree.
The changein mud properties,otherthen weight,
seem to affectthe equationin the same genersl
manner as was proposedby Eckel.7 me d~g
rate is affectedby tiscosityby a value
approachingthe 0.5 power of the changein the
Reynoldsnumber. For smd.i changesin tine
viscosity-relatedterms there is no apparent
effect on drillingrate.
Large changes,how-
ever,particularlythose increasesin tiscosity
causing significantchangein the Reynolds
number, can make the pressureequationinoper-
able. No attemptis made at this ttie to
make
these correctionsmathematically. Some
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BILL REHM and RAY McC~tDON
prelimfia.ryork indicatesthat the Reynolds
n~mner cn~~~ct~o~ ~~obably could be made in such
.----
a manner as to cor;ecifor some of the tiscosity
Ck. ge.
With nigh viscositiesthere is no data
to indicatewhetherthe equationcould be made
valid or not.
Viscositiesmay introducesome
factorsin holecleaningthat we are unableto
handleat this time.
The effect of mud weight is more straight-
forward and the mud weight correctionallows for
these changes.
There is, however,a problem
hvolvedti.the mud weightcorrectionmuch akin
to that of viscosity. Wnen the mud weight is
more than 2 or 3 lb/gal.greaterthan the for-
mationpressure gradient,or the bottom-hole
presswe is ~reaterthan 1,000 to 1 500 lb more
than the fo~ation pressure,the solution
becomes erroneous. In general,the solution
indicatesa highermud weightthan is actually
needed. It appearsthat the drillingrate vs
differential-pressurecurve (Fig.I)-is on the
flat part of the slope and shows no effect of
increasedor decreaseddifferentialpressure.
The functionrelatingto increasedporosityis
not able to make the total correction.
RESULTS OF PRESSUREPLOTS
The field work done with the data collec-
tion units provideddrillingrate/pressure
plots of exceptionalaccuracy. The plots were
made utilizing only pure shsle or some other
agreedupon standard.
Tne potitspicked as
representativewere checkedagainstlagged
cutting samples.
Becauseof the accuracyof the
data co~ection equipment,it was possibleto
use representativedrillingvalues throughthe
standaxdsection.
The dcs
value was plotted
on the standardscale and the overlayapplied.
For the most part the solutionswere accuratetc
within 0.2 lb/gal of formationgradient.
While
it was possible in some cases to compareto
pressurevalues obtainedduring a well kick or
---a..+
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MEZkSURINGORMATIONPFU3SSUR.EROM DRILLINGDATA
WE 3601
1
ecord can be used to supportthe log calcu-
ationsby means of Ecp. 4 and 5.
The effect
7
itnologyis unhewn; however,pressure
culationsder5Lvedb this mannerare ama-
accurate.
Thepressure tiWidS are
eciallygood, but with accuracylimitedto
out 1 lb/gal (Fig.7). Otherproblemsfith
t recordplots involve the difficultyin
ining any idea of correctionsmade for hole
ation. While dri2J_ingassemblychangesand
rJ light bit weights shouldbe indicatedon
record,more often tk,annot informationis
IERCCMFARISON
The exceptionalaccuracyexperiencedin
e field,raisedthe questionof using the
rlayand plot.
To controlthe titerpreta-
on by field personneland to maintainstrict
dards,a computersolutionw preparedby
ldingEqs. 4 and 5A together. Sinceitwas
annedto use an automaticplottingtechnique
s well
as derivingan answer,the equationwas
rthermodifiedto reduce the normal slope of
e decreaseh drillingrate with depthto
rticaiand to give the answerml a eomiinate
er than logarithmicaxis.
This term was resolvedas
[ ~2Lo~
f=c7.62Log Ha + C - ~LOg 60N
+16.52 , . . . . . . . . . . . . (6)
here P =
formationpressuregradient,lb/gsl
7.6 = slope constant
H = geologicaldepth, ft
a= slope of the
noxmal
penetrationrate
for the drill tools involveddcs
units/ft
= drillabilityconstantdc units
16.5:= interceptconstant,lb/gaf
The computergave essentifiy the same
olutionas did the hand plots (Fig.8). In
on-sitework, the variousparameters,wit-n
he exceptionof a and C, were enteredauto-
ALYSISOF THE NOMENCL4TUEE
Mud weight in poundsper gallonwas selec-
ed as a usable field texm. he use of a mud
texm is particularlyconvenientin the
eld for comparisonwith the mud weightin use
Slone Constant(7.62>
~i~ is the slope of the line of the plot
of lb/galVS dcs.
It is the slope of the
m.--v.vfrom Eq= 5A Or 0.398/0052.
G.&.aJ
,=..
g
This
term is genertiy used as T.V.D. in
feet.
However,the properdescriptionof the
texm is geologicaldepth. This shouldbe
correctedfor faulting,major foldingend
possibleu~lift.
The majorityof the work with
this equatzonhas been done in basin
areas.
Limited data indicatesthat the effectof up-
lift can be correctedby use of a reconstituted
depth.
g
This is the slope of the normal dcS. In
the most straightforwsmiversionof the equa-
tion, the term & actuallybecomesdcs for
the normal-pressuredzones. This is then ex-
tended to the overpressuredzonefor compara-
tive purposes. It is a vfid approachand is
~Acm,~Iydgp.evltb.had-plotted solutions. In
the case of an automaticplot, it is easierto
handle the circuitryor programwith a slope
term.
The slope term ~ is quiteconstantwith
geologicalage.
Tnere is, for exampie,very
little variationin the slopevalue a between
the Miocene of Louisianaand lndones~a.
:
The tilability constantis actualJ.ythe
drill tool constant. DifferentdriJJ.ingrigs,
formations,and differentcustomschangethe
absolutedcS.
In the basic d
equation the
value Q for any rig is correctedby inspection.
InterceptConstant(16.52)
The interceptconstantis the offsetvalue
fromEq. 4 (0.86/.052).
Mwl
-2 . & 4. +h. me- 1 nmmee??vm
L1lA=
U@LIU +- U..G ..w.m~ F. ---- -
gr=dfi~~~
for the area.
MW2
This term is the mud weightin use cor-
rected for the circulattigdensity. The equiv-
alent circulatingdensityis an importantcon-
siderationindeep slimholes.
~
This term is the drCMng rate in feet per
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WAS TRTNG F XWATTON ? ESSUFE FROM DRILLINGDATA SPE 360
. ----- ------------- - -- --- .
(195 )~, 9-17.
Pet. Zn~. (Nov.,1969).
6. Dolpk, ;. R. and 3rown,K. E.:
Zffec?.of
IL
Jorden,J. P..and Shirley,O. J.: ..
~Aa~~
Rota.qySpeed and Bi~ tiight on Penetration
cationof DrillingPerformanceData to
Rate of a DiamondMicrobit,
J. pet. kch.
Overpressure
Detection,J. Pet. Tech.
(Sept.,1968) 915-916.
(Nov., 1966) 2387-1394.
7. Eckel, J. R.:
Tiicrobittudies of the
15.
Jorden,J. R. and Shirley,O. J.: Tfeth
Effect of Fluid Propertiesand Hydraulics
for Detem~ the Top of Abno~al Foma-
on DriilingRate,J. Pet. Tech. (April,
tion Pressures,U.S. Patent3368&O0,Feb.
1967) 5u-546.
13, 1968.
~a
**HowMud and ~yaratics
.rkel.J, R=: -----.
16. MaurerfW. C.:-..--, Bit-ToothPenetration
AffectDrill Rate,
Oil and Gas J. (June
Under SimulatedBoreholeConditions,~.
17, 1968).
Pet. Tech. (Dec.,1965) 1433-1U2.
9* Fcm? 7--A
Luyu ad Imt rein:
Wrm-. 4
ru4utau*O~i
~?e M,,W-F..W
.,WAW, ~= ~= @ ~l&n~~@~f R, A,:
Log ?ressu.reData Can ImproveDrilling,
? Effectof Mud COl~ pressureon Drillin
World CKL (Sept.,1966).
Rates, TYans.,AIME (1955)~, 196-20L.
10. GaX1.e,E. M. and Woods, H. B.:
Best
18.
Outmans,m.:
The Effect of Some
Constan;Bit Weight and Rotary Speed,
DrillingVariableson the Instantaneous
011 anc Gas J. (Oct.,1963).
Rate of Penetration,Trans.,
AIME (1960)
1. Gamier, A. J. and van Lfi.gen.N. H.:
219,~37_~49.
PhenorenaAffectingDrillingRates at
19*
~tison, L. H., Jr.:
Effectsof Pore an
Depth, Trans.,AME (1959)~, 232-239.
ConfiningPressures
on Fa ilw e
Character-
12.
Hottman,C. E. and Johnson,R..K.:
Esti-
isticsof SedimentaryRocks, Trans.,AIME
mation of FormationPressuresfrom Log-
(1959)~, 26-32.
Derived Shale Properties,J. Pet. Tech.
(June,1965)717-722.
20. Vidrine,D. J. and Benit, E. J.: Field
Verificationof the Effect of Differentia
Jones,F. T. and Barringer,S. H.: lm-
Pressureon DrillingRate, J. Pet. Tech.
proved Communicationswitinthe Drill Bit,
(Jtiy,1968)676482.
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000
10000
12000
I II
d
C*
1.0
2.0
(
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ACOUSTICS
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