api-36-008 (use of recording pressure gages in drill-stem tests)

8/10/2019 API-36-008 (Use of Recording Pressure Gages in Drill-Stem Tests)

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Use

of

Recording Pressure Gages

in

Drill Stem Tests

R

S.

HRISTIE

ABSTRACT

The author defines briefly the drill-sten1 test em -

when making this test nd discusses at length the inter-

phasizing the inanortanre of obtaining a pressure record

pretation of records obtained.

drill-stem t est may be made to obtain indications of

the potentialities of a suspected oil o r gas sand to test

fo r water shut-off af te r cementing pip? or to determine

the casing point in a known producing horizon. The

drill-stem test is obtained by running on th e bottom of

the drill pipe a valve which can be opened and closed

from the surface. All the formations in th e hole ar e

packed off with the exception of that section of the hole

to be tested. The drill pipe is run into the hole with the

testing-tool valve closed. Aft er t he packer has been set

the valve i s opened; a nd liquid or gas a t the testing point

ente rs the drill pipe. I n all cases the success of the test

depends on the successful operation of the testing tool.

Whether o r not the valve functions properly can be quite

positively determined on the surf ace f or shallower wells

but becomes less positive with increasing depth. It is

important to obtain a s much information a s possible on

each test.

In a test fo r wate r shut-off ther e is little or no open

hole below the casing in the well close to the point of

testing and consequently small hazard. On the other

hand a formation test or casing-point test is usually

made with several hundred feet of open hole with re-

sult ant dang er of sticking the drill pipe by settling cut-

ting s or caving. If i t becomes necessary to run th e test

several times the walls may be weakened and cause

trouble when drilling is resumed.

A kecord of the changes in p ressu re below the testi ng

tool will make more positive the information ordinarily

obtained by such a test and frequently give informa-

tion t ha t could not otherwise be obtained. A recording

pressure gage can be placed into a special container

which can be a part of the anchor of the testing tool.

Fig. shows one type of container.

Purpose of Test

The primar y purpose of a drill-stem te st i s to deter-

mine whether a given formation contains gas oil or

water. The test may give negative results in the face

of other positive indications. This is particularly t ru e

in deep holes a s it i s not always possible to ascertain

whether the packer is holding and the valve function-

ing properly. When the va lve is opened and the fluid

Amerada Petroleum Corp.. Fort Worth Te s.

does not lower appreciably a t the top of th e hole it i s

assumed the test is successful; but this is not always

true because the fluid may drop due to leaky tool joints

Container for Pressure Gage for Use in Drill-Stem Tests.

FIG 1

or because of loss into some formation or may fluctua te

due to gas or ai r pockets-all despite the fac t th at the

packer may have held and the valve opened to give a

test. To eliminate an y doubt a s to the mechanical opera-

tions of the tester a recording pressure ga gs below the

teste r will record differences in pressures occasioned by


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Pressure I l s p m

IDW ooo aow

USE

OF

RECORDING RESSUREAGES

N

DRILL STEMTESTS

Pressure bs

JV

he operation of t he tester.

Fig. 2 shows how the tester

unctioned in a well a t a depth of 5 685 ft. The test was

for a water shut-off. Without th e pressure record the

est would have been int erpreted a s a successful shut-

ff. A subsequent test proved th at wa ter was not shut

off. Fig. 3 shows a tes t taken on a well a t a depth.of

3 463 ft. At the end of about 5 min. the full weight of

the dril l pipe was on the packer. The fluid dropped

Drill-Stem Test of Water Effect of Pressure of Par- Pressure changes in a Drill-

Shut-off at 5 685 Ft.-The tially--plugged Perforations or Stem Test of a Gas Sand.

degree of accuracy t he capacity of th e well to produce

whether i t be gas, oil, or water. In a gas well the open

flow can be determined from the drop in pressure and

the ra te of flow. Fig. 4 is a pressure chart taken in a

well which produced gas a t the rat e of 5 400 000 cu.

ft. per day, with a drop in pressure of 262 Ib., from

a reservoir pressure of 983 lb. The colnputed open-flow

capacity of t he san d is about 20 million cu. ft. of gas

Testing-Tool Valve Failed to Choke in the Testing Tool.

Open.

FIG.

FIG.

3

bout 30 ft. During the total time of 33 min. there was

o change in the fluid. level until the valve was closed..

From th e irreg ular ity of the ch art an d from indications

n the surface, it is reasonable to believe the bottom

hoke wa s part ially plugged. With a small opening and

h differential pres sure when t he valve is opened,

uch a result may be obtained.

An analysis of the pressures recorded shows whether

testing tool functioned properly, and indicates other

ulportan t factors. I t is possible to obtain with some

FIG. 4

per day. The sta tic reservoir pressure was ,obtained

by not unseating the packer for 2 min. after the bot-

tom valve had been closed, which was sufficient time

fo r a p ressure ,reading. A st atic reservoir pressure ob-

tained a t this s tag e of completion will be

Inore nearly

the original formation pressure than any subsequent

pressure.

Oil-Well Application

A similar method can also be applied to an oil well,

bu t sufficient tes ts have not a s yet been obtained to de-

term ine dependability. Fig.

5

presents data obtained


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on a drill-stem te st taken a t a depth of 4,418 ft. With

th e tes ter valve open 20 min., 614x1. dril l pipe filled 900

ft . with oil and 180 ft. with drilling mud. On this basis

the calculated flow was 102 bbl. per hour, with a bot-

tom-hole pressure of approximately 300 lb. A produc-

tion test after completion obtained approsinlately 60

bbl. an hour, wi th bottom-hole pres sure of 1,150 lb.

and a low gas-oil ratio. Fig . 6 shows the results of a

drill-stem test th at produced water. The test was taken

5m

Pressure l s q

m

lorn 1600 2000

may show a section of mud th at is gas-cut and much

lighter than the remainde r of the column. Fu rth er test-

ing may prove this to be caused by a gas- or oil-bearing

formation which has been passed up.

Even though no

other formation is obtained, a pressure gradient gives a

graphic p ictu re of the condition of th e mud in the hole.

From such a picture it may be found advisable to con-

dition the mud before further testing or drilling ahead.

I n Fig. th e measured hydrostatic head was 2,915 Ib.

Pressure Changes in a Drill- Drill-Stem Test of a Water Drill-Sten1 Test of a Water

Stem Test of an Oil Sand.

Sand at 3 270 Ft.-Calculated

Sand at 5 704 Ft. and Check for

Plow

60

Bbl. Per Hour.

Mud Condition.

FIG.

5

FIG.

6

FIG. 7

a t a depth of 3,270 ft . The decrease in pres sure between

the making up of the last stand of drill pipe and the

setting of the packer may have been caused by the

formation tak ing fluid. Fr om the volume of fluid in

the drill pipe, the estimated flow was approximately

60 bbl. per hour. The bottom-hole pressu re while flow-

in g at this ra te w as 1,424 lb., which is sufficient pres-

sure for an artesian well.

The hydrostat ic head calculated from the weight of t he

mud was 2,930 lb., which proved the entire colunln of

mud was in good condition. Occasionally mud is heav ier

than necessary, bu t tests of formation pressure ar e more

likely to prove th at for safety the mud should be

heavier.

Well Completion

Pressure Gradient

While running th e gage, a i~ res su re radient of the

drilling fluid is also obtained. A study of this gradient

Many wells a re completed by landiiig pipe on bottom,

then perfora ting the pipe a t those points where indica-

tions of oil were encountered while drilling. drill-

sten1 test of t he perfora tion may frequently he quicker


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and more economical than bailing. The pressure record

of such a test shown in Fig.

8

will aid in interp retation

of th e test. When th e bottoln valve was opened the

pres sure dropped to allnost 0 and only small gas blows

by heads occurred during the hour the valve was open.

I t was known from a previous drill-stem test th at th e

potential of t he s and wa s much gre ater tha n was ob-

tained by the lat er test. Several additional perforations

and test s were required before sufficient information w as

gained to permit p rope r completion of t he well.

The usual method of t estin g a cement job i s by bail-

ing th e hole and allowing i t to stan d to determine if fluid

is entering the hole. Freq uen tly a drill-stem test can be

substituted . This method will prove whether a shut-off

valve

v lve

opened

closed

Drill-Stenn Test after Perforating Pipe in a Gas Horizon

at

4 005

Ft.

FIG.

8

is obtained and often a t less expense. The pressure

gage will show the amount a nd ra te -a t which the wate r

is corning into the hole if th e shut-off job is unsuccessful.

Fig. 9 is a pressu re record of a n unsuccessful wate r

shut-off. The hole contained wate r a s a drilling fluid.

The drill pipe was run into the hole empty; and upon

opening the tes ter valve approxima tely 30 min. was

required to fill the drill stem up to the top and flow a

small amount of water.

Fig.

10

is a pressure chart on a drill-stein test of a

successful shut-off. When pulled out the drill pipe con-

tained nothing bu t 5 ft . of mud in the bottoni.

CONCLUSION

drill-stem test is usually a satisfactory method of

testing a formation to determine the advisability of

setting pipe fo r a production test. I t is much more sat-

isfactory when t l~e


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estimated, the reservoir p ressure measured, an d the con-

dition of the drilling fluid determined. Additional ap-

plications are determining the success of perforation

jobs, wate r shut-off jobs, a nd i n testing fo r casing seats.

Just as all improvements in the drilling and produc-

ing of oil wells become st an da rd practice, so also will

the use of recording pressure gages in drill-stem tests

hecorne an essential pa rt of th e test.

Chairman

J

T. Hayw ard (Barnsda ll Oil Company)

We have heard a very interesting paper, and on some-

thin g th at is absolutely new. I understand th at a num-

ber of tests shown here were only taken during the

las t month. We have all stood around the top of the

hole when drill-stem tests were made, and watched

the mud. Aft er a longer or shorte r time, depending

on conditions, it begins to fall; and, when the tester

was pulled out, we had to guess whether there was

anyt hing ther e or not. Usually, 50 per cen t of the

guesses have been wrong, I suppose. Now we have a

method t ha t enables u s t o overcome th at difficulty.

G

E.

Cannon (Hum ble Oil and Refining Company)

The author states that 2 min. was long enough time to

obtain the forma tion pressure. We used similar methods

in making tests, and found that the maximum pressure

was not obtained until the end of 15 min. Of course,

our plan vari es fr om the, one you use.

Another peculiar t hi ng was th at, in some of these

tests, just before the packer was set, a record was ob-

tained of the hydrostatic pressure, and aft er unseating

the packer, there was a reduction in the hydrostatic

pressure by as much a s to 10 per cent, and there was

no loss of fluid.

I

thought that was quite interesting.

Mr. Christie: Th at is a n unusual condition. I t might

be well to ru n a recording gag e in the pipe and outside

of it. Pe rha ps some of th e loss is due to leaky tool

joints, and going into th e tool pipe.

Mr. Cannon: No, th e hole wa s full of mud. We set

the packer; and, aft er unseating the packer, it was full.

There was no loss there.

Mr. Christie: I have no explanation for that.

A Voice: The aut hor cites a case where the calcu-

lated flow was 102 bbl. pe r hour with a bottom-hole pres-

sure of approximately 300 lb., and another instance

where the production t est w as 60 bbl. a n hour, with

bottom-hole press ure of 1,150 Ib. I s t ha t indicative of

the accuracy of the test?

Mr. Christie: As a m att er of fact, the pressure

obtained on the drill-stem test fell almost esactly on

the production curve aft er completion. We had a pres-

sure here of 1,150 Ib., with 60 bbl. a n ho ur on the pro -

duction test; and on the drill-stem test we had 102 bbl.,

with a pres sure of 300 lb. Of course, th e first test, unless

taken for a considerable length of time, is not a t ru e

test, because i t takes some time for th e sand to clean up.

We have subsequently taken a second test in that well,

and i t shows the well to have dropped off some. I t

didn t follow the fir st curve.

api-36-008 (use of recording pressure gages in drill-stem tests)

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