gas well testing - storage

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SOCETY OF PETROLFUM ENGINEERS OF AlME

6300 North Central Expressway

Dallas

6

Texas

PAPER

NUMBFR S P E

9 2 3

THIS IS A

PmPRINT

SUaTECT TO CORRECTION

GAS

WELL

T E S T I N G - - - S T O R A G E

Donald L. Katz, Member AIME, U. of Michigan,

nn

Arbor, Mich.

Publication Rights Reserved

This paper i s t o be presented a t th e 39th Annual Fall .Meeting t o be hel d i n Houston, Tex., on

Oct. 11-14 1964, and i s considered th e pro perty of th e Society of Petroleum Ehgineers.

Permission t

publ ish i s hereby res t r i c t ed t o an abs t rac t of not more than 300 words, wi th no i l l us t r a t io ns , unless

the paper i s s pe ci f ica l ly re leased t o the p ress by the Edi to r of t heJo urn al of Pet roleum Technology

the Executive Secretary.

Such abs t rac t should conta in con sp icu ~u sa ck no wl e~ en tf where and by whm

the paper i s presented.

Publicatio n elsewhere a f t e r public ation i n ,Jou rna l of Petroleum Technology

So cit y of Petroleinn Engineers Jo ur na l i s granted on reques t , providing proper c red i t i s given th at

publ icat ion and the or igi nal presenta t ion of the paper.

Discuss ion of t h i s paper i s invi ted .

Three copies of any disc ussi on should be se nt t o the S oci

of Petroleum Engineers office.

Such di scu ssi on may be pres ente d a t th e above meeting and conside red

f o r pu bli ca tid n i n one of t he two SPE magazines with th e paper.

ABSTRACT

The usual back pressure te s t s o r inf low tes t :

during gas i nje cti on are needed t o understand gas

well flow cap acit ie s . Such indi vid ual we ll capa-

ci t i es are combined in to composite f ie ld del iver-

ab i l i t y curves f or p red ic t ing the f lowing we l l

head pressure during heavy gas withdrawal periods,

Some pra cti ces f o r gas storage i n both depleted

gas f ie ld s and aquifers a re discussed.

Gas wel ls ar e te s te d reg ula r i ly i n connect ior

with storage operations

. l j 2

Two ty pe s of re se r-

vo i r s w i l l be considered; depleted gas fi e ld s and

aquifer s torage f i e l ds . Generally, the object ive

i s t o know the flow capa city of t he gas wells

during the high withdrawal periods.

DEPLETED GAS FlELaS

The flow capaci ty of gas wells i s normally

dete rmined sh or t ly a f t e r d r i l l i ng . A t t h e tim e oJ

convers ion of deple ted gas f i e l ds t o s torage,

it

i s advisable to re - t e s t the we l ls fo r de l ive r -

ab i l i ty . Such te s t s usual ly must

w a i t

u n t i l a

reasonable degree of rep ressu ring has taken place

t o g ive enough gas pressure t o permit blowing th e

wel l s and t o as sure tha t the we l l s and face i s

dry.

A comparison of t h e re -t es t performance

with the or i g ina l t e s t ind ica tes the degree of

deterioration and whether remedial work i s i nd i -

cated. Fig. hows a St ra y Sand gas we ll with

severe de te r io ra t ion during i t s p roduct ive l i f e .

i e ~e r e nc e s nd i l l u s t r a t i on s a t e nd o f paper .

Any new wel ls d r i l l ed ar e tes te d t o give th ei r

flow capacity.

The information of interest i s the compos

performance curve fo r the f i e l d. This i s obta i

by takin g the sum of t he flow cap ac itie s

[Q]

given diffe renc e of squares of the pressures.

Such a fi e ld curve along with the ga thering s ys

pressure drop w i l l give the f i e ld de l ive ry pres

sure fo r any flow ra te and gas reser voi r pres-

sure . l r2 The reserv oir pressure i s of ten observ

di r ec t ly by a pres sure obse rva tion we l l t o f i nd

Pf

Flow t e s t s ar e most conveniently taken

in

summer time i n per iod corresponding t o gas

inject ion ra ther than wi thdrawal . It has been

shown that inflow testing gives the same resul

as ou tf low tes t in g l-3 and Fig . hows inf low

te s t re s u l t s a f t e r conversion to gas s to rage .

w e l l t e s t i ng

it i s

customary t o use deadweigh

pres sure gage f o r wel l head p ress ure measureme

and ind ividual wel l o r i f i ce s meters.

The re la t iv e clo se spacing of gas wells f o

sto rag e removes th e us ua l problem of un steady

s ta te . However, before developing a res erv oir ,

i n i t i a l t e s t s on a gas we l l involving unsteady

s t a t e may be made i n t he manner followed by

~0 be rt so n. l The more l i ke ly problem i s th at a

portion of the gas reservoir has high permea-

b i l i t y nd hence contain s most of t he de live ra-

b i l i t y capac ity . Edge we l l s in the l e s s pe r-

meable sand may repr ese nt con side rab le sand


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volume but a small por t ion of the d el iv er ab il i ty

Readers a re re ferre d t o the s tudies of Glass and

~ e s s u n g ~r t o the method of p lot t in g observat ion

wel l pressures vs gas content of reserv oir f o r

sucessive injec t ion cycles .1

By t e s t i n g t h e we l l s

i n a f i e l d a t one o r twc

yea r in t e rva l s , it has been possible t o predic t

f lowing compressor s ta t ion in le t pressures f o r a

given observat ion wel l pressure and f low ra te t o

within

-5

t o

8

p s i .

AQUIFER

STORAGE ESERVOLRS

A n

ear ly s tep i n developing an Aquifer s to r-

age rese rvo ir i s the cor ing and te st in g of cores

on the storage sand.

As a f i r s t approximation;

the permeab il i ty of the cores, sand thickness, an(

pos tula ted pres sur e con ditions can be used with

steady s ta te f low formulas t o pre dic t the capacik;

of t he w ell f o r gas when th e gas bubble has been

developed o r the fi gu re on page 439 of Reference I

may be used t o fin d the de li ve ra bi l i t y curve.

Should pumping d ata be taken on th e water w ell t o

asce r ta in the in s i t u permeabil i ty , procedures

described5 such perm eab ility may be used i n place

of the core data.

The e f f ec t of a pa r t i a l ly pene t ra t ing we l l

should be noted when making such flow calcula-

6

ti o n s . The ch ar t developed by Muskat per mit s an

approximate correction f o r sand thickness t o be

used i n flow calc ula tio ns depending upon th e thick

ness of gas bubble and wel l pen etrat ion .

Once gas has been in jec ted in to th e

a q u i f e r

t o form a gas bubble and th e sand face has been

dried by the injec ted gas, the usu al back pres-

sure t e s t o r inf low t e s t can be made on the gas

we l l .

It

i s obse rved th a t t he in j ec t ion o f gas

requires le ss pressure drop as th e water i s

removed from the sm d adjacent t o the inj ec t ion

we ll. For a given we ll completion, bu t with

thickening gas bubble, the flow capacity should

increase due t o th e contribu tion made t o flow by

th e non-penetrated sand.

Most wells in a given reservoir may be ex-

pected t o have the same slope of th e back pres-

sure curves. Fig. 2 i s a mul t ipo in t curve fo r a

Herscher Ga les vil le sand wel l. The flow ra te

points were taken by a c r i t i c a l f low prover while

the higher f low ra tes were taken wi th the individ-

u a l w el lm et er . This curve when checked with

oth er wells was considered t o represent th e slope

f o r a l l w e lls .

In cons tructing th e f i e l d curve, one would

normally add the ind ivid ual well f lows a t a f i x e d

difference of squares and use the slope estab-

l i s he d f o r t h e f i e l d . A t Herscher, some Gales-

v i l l e we l l s, F ig . 3 have such a high flow capa-

c i t y t h a t it i s d es ir ab le t o r e s t r i c t t h e i r flow

t o

35

mill ion cu

t

per well per day.

Thi s ra t e

was established [28 f t p e r s eco nd l i n e a r v e l o c i t y ]

NG STORAGE SPE-923 r AGAS WEU TEST17

3

as t h at which would not permit sand t o cu t th e

we ll head i n a short t ime. When re st ri ct in g tho

wells which reach a flow capacity of 35 mil l ion

cu ft per day, th e composite f ie l d curves take

th e form shown i n Fig. 4.

.During th e 1962-63 w ithdraw al. season, two

flow t e s t s were made f o r the Herscher G alesvil le

f i e l d performance with t he da ta shown on Table 1

A

comparison of th e f i e l d performance with th e

predic t ion curve prepared a year e ar l i e r i s show

on Fig. 4.

Once the equil ibrium water l e v el i n an

aquifer recedes s ig ni f ica nt l y below the perfora-

t io ns of th e producing well , most of th e wells

remain f re e of li q ui d water and th e we lls may be

expected t o match t he performance predi cted from

i n d iv i d u al we l l t e s t s .

EFFECT OF WATER PRODUrnION

A common problem i n p rod ucin g a group of

wells from

a

colmnon re se rv o ir i n t o a common

gather ing system i s in te rference by water i n the

f lowing ve r t ic a l column. Fi rs t the increased

dens i ty of the ve r t i c a l

column reduces the back

pre ss ur e of any w el l producing more water th an t

average. A t some gas flow rate and water rate,

l iq uid accumulation i n the wel l bore increases

sign i f ica nt ly , fur the r decreasing the f lowing bo

tom hole pressure.

What

i s

needed i s

a

quick

means of t e l l i ng t he opera tor when a wel l i s a t

flow con ditio n where accumulation of water i n th

we l l bore i s abou t t o t ake p lace.

This requires

measurement of th e water ra te , th e gas ra te , and

flow string dimensions.

Tests and re la t ionships

t o handle such water problems would be hel pf ul .

The information provided by J A. Vary and

J

R. Elenbaas of Michigan Consolidated Gas Co.

and by 0. C. Davis and

W

M Rzepczynski of

Natur al Gas Pipelin e Co. of America i s gra te fu ll

acknowledged.

EFEFaNCES

1 Katz, D. L., Cornell,

D.,

Kobayashi,

R.,

~oet tmann,

F H.,

vary, J A., ~ l e n b a a s ;

J R. and Weinaug,

C.

F.: Handbook of Nat-

u r a l

Gas

Eugineering, McGraw-Hill Book Co.,

Inc., N. Y. [1959].

2. Katz, D. L.,

Vary

J

A.

and Elenbaas, J

R

m e Design of Gas Sto rag e Fi eld s , Trans.,

AlME [19591

216

44

3

Vary, J A., Elenbaas, J R. and Withrow,

H.

J

: In'put Flow Te st Method f o r Determi

t i o n of Well Performance , Paper pre sen ted

Research Conference, U. of Michigan [l9551.

4.

Glass, E. D. and Hessing, R.

C.

: A Method

of Computing Pressure Behavior and Volume o

Gas Sto rag e Rese rvoir , Jour. Pet. Tech.

[19621

2

544.

5. Katz, D. L., Tek,

M .,

Coats, K. H., Ka-tz


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SPE -923

[ ]

DONALD

L.

KATZ

M

L. Miller

M C

nd

Jones

S.

Move-

ment of as i n Contact w i th

Natural

Gas

Am

as

Association [1963].

6. Muskat Morris . Phy sical Pr in ci pl es of

O i l

Pr oduc tio n McGraw-Hill Book Co. In c.

N Y

T19491.

TABLE I

CALCULATIONS OF FIELD DELIVEWILITY

DURING THE

1962-63

WITHDR W L

SEASON FROM TH GAIZSVILLF: SOUTH FZSERVOIR

Date

D e c

12 1962 Jan . 21 1963

No. of Flowing We lls

Shut-in Pres sure Pf

Wellhead psig

Reservoir ps ia

Flowing Pr ess ure Ps

Wellhead psig

Reservoir ps ia

i n ~ h o u s a n d s

Flow Volume

M C ~ D


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Figure 1 Back Pressure Curves Reed City 34 Well Stray Sand.

Figure 3 Performance Curves of Individ ual Galesville Wells.

F L O W R A T E . M I L L I O N cu.

ft

per D A Y

Figure 2Muitipoint Flow Test on H era her Galesville Well.

F L O W R A T E . M I L L I O N S c u. ft

per

D A Y

Fgu re 4 Composite Field Deliverability Curve

o

The Galesville South Reservoir.

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