BMR Record 1988/47 ~, r r - --. ...... :: r

TIDAL EFFECTS IN WEST KINGFISH

PULSE TESTS, DECEMBER 1987

BY

D.J. WRIGHT

CONTENTS

SUMMARY

INTRODUCTION

PULSE TESTING METHOD

BASIC DATA

TIDAL EFFECTS

ANALYSIS OF PULSE RESPONSE

DISCUSSION OF RESULTS

CONCLUSIONS

REFERENCES

ACKNOWLEDGEMENTS

FIGURES

1 Location of West Kingfish wells

2 Well flowrates and pressure response

3 Pressure response with data shifted

4 Pressure response without periodic effect

5 Pulse test analysis

6 Pressure response and tidal effect

7 Pressure response without tidal effect

TABLE

1 Tidal Maxima and Minima

PAGE

1

2

3

4

5

6

8

9

10

10

12

13

14

15

16

17

18

11

1

SUMMARY

On 12 and 13 December 1987 two pulse tests were carried out on the West

Kingfish platform, Gippsland Basin, between the West Kingfish wells W-1

and W-6, and W-1 and W-19. The results of these tests indicate a tidal

effect is present, masking the response signal. This effect corresp·onds

to the tides at Eden, with a tidal efficiency of 0.19 psi/m tide height

and a time lag of 1 hour.

When the tidal effect is subtracted, a positive first response to the

pulse test between wells W-l and W-6 can be detected, possibly indicating

communication between the wells and giving results consistent with the

formation propJrties. No communication is detected between wells W-l and

W-19.

f

I 2

INTRODUCTION

Pulse testing is a method for determining reservoir properties between two

wells by measuring very small pressure responses due to a series of flow

disturbances. In ideal cases the response amplitude and the time lag of

the response can be useful to determine quantitative values of

transmissibility (kh/~) and storage (~ch). In addition, even when the

conditions are not ideal, qualitative information about flow anomalies,

fractures, and between-zone communication can be obtained.

Two pulse tests were carried out on West Kingfish platform in December

1987 between the wells W-l and W-6, and the wells W-l and W-19. The

location of these wells is shown in Figure 1. The purpose of the pulse

tests was to determine whether measurable communication existed between

the wells being tested. The tests were carried out using a HP quartz

crystal gauge, so that responses as small as 0.01 psi could be detected.

3

PULSE TESTING METHOD

The tests were carried out in the following manner. A bottom-hole

pressure gauge was installed in the shut-in well W-1 and pressure

recording commenced at 1 pm on December 12. Well W-6 was shut-in at 2 pm,

and flowed again at 7.30 pm giving a first pulse duration of 5 1/2 hours.

It was shut-in again at 1 am on December 13, and flowed at 6.30 am, giving

a second pulse duration of 5 1/2 hours. This completed the pulse test

between W-6 and W-1 - two shut in periods of 5 1/2 hours separated by a

flow period of 5 1/2 hours.

Well W-19 was then shut-in at 9 am on December 13, and flowed again at

6 pm, giving a 9 hour pulse. The well was shut-in finally at 3 am on

December 14, and pressures were recorded for 5 1/2 hours after this. The

W-19 pulse test thus consisted of one shut-in period of 9 hours followed

by one flow period of nine hours.

Figure 2 shows the periods during which the various wells were flowing and

shut-in, and the pressure response in the bottom-hole quartz crystal

pressure gauge in well W-1. The data is discussed in the following

section.

4

BASIC DATA

The uncorrected data plotted at approximately 15 minute intervals

(Figure 2) show two outstanding features. These are

(i) the pressure peak at approximately 15 hours

(ii) the cyclical nature of the pressure response between 20 hours and

the last pressure reading at 57.7 hours.

At first sight, the response in the later time periods appeared to

correspond to typical tidal rise and fall curves. The data from 33 hours . I

(9 am on 13 December) were shifted forward and'superimposed on the earlier

time data until a good match was achieved over most of the period. At the

point of match the later data had been shifted 24.53 hours suggesting a

tidal cycle of this duration. This is seen in Figure 3. The later data

seems to show purely tidal effects. When the (shifted) later data are

subtracted from the earlier data, the net response should show little or

no tidal effect. This was done and is shown in Figure 4 (on the same

scale as Figure 3) and in Figure 5(on an expanded scale). A strong

positive response of about 0.15 psi is evident at 15 hours. A possible

negative response is also evident at 20 hours.

I 5

TIDAL EFFECTS

The next step was to investigate the apparent tidal effects further, to

see if they were consistent with expected tidal effects in the Gippsland

basin. Clearly, the tidal effect will be the result of earth, ocean and

atmospheric tides. The Gippsland aquifer, which underlies all the oil and

gas reservoirs, is open in the Gippsland hills to water intake, and is

believed to be open to the ocean on the continental slope. It may

therefore be over-simplifying to interpret the expected tidal response

only in terms of ocean tides at the location of West Kingfish.

The Australian National Tide Tables for 1987 (Department of Defence, 1986) I have two "standard ports" near the Gippsland Basin - Eden and Westernport.

Table 1 shows the tidal maxima and minima for the period in question at

these ports. Note that the average tidal period is about 24.7 hours, not

far from the figure of 24.5 hours derived only from "shifting" the

pressure data to obtain a good fit. The best fit to the observed pressure

data is given by the tides at Eden to the east. Interpolation between

high and low tides was carried out using the graphical method described in

the Tide Tables.

The resulting tide heights delayed by one hour are shown with pressure

data on Figure 6. The fit with the observed pressure data is very good.

The multiplying factor to achieve this good fit is 0.188 psi/m. A

corresponding value of the multiplying factor for Jabiru lA was 0.28 psi/m

which is higher but of the same order of magnitude.

The result of subtracting the predicted tide pressure effect (lagged by

one hour) from the basic pressure response in shown in Figure 7.

This is similar to Figure 4 and shows the unusual peak at an early time,

possibly resulting from the shut-in of well W-l.

6

ANALYSIS OF PULSE RESPONSE

The data shown in Figure 5 can be analysed by the "tangent n method. The

lines shown on Figure 5 represent approximate tangents to the pressure

traces, drawn parallel to each other and touching the pressure traces at

three points.

The pressure difference indicated by A. pa on the figure indicates the

positive pressure response to be analysed. The time lag is the time

between shutting the well in at 2 pm on December 12, time = 14 hours and

the time at which this peak response occurred.

The minimum indicated by ~pb indicates a possible negative pressure

response, resulting from flowing the well at 7.30 pm on December 12 (time

= 19.5 hours).

First Positive Response

The well A-6 was shut in at 2pm on December 12. The maximum positive

response occurs at approximately 3.15 pm, 1.25 hours later (tLl ). The

producing time of the well was 5.5 hours (A t). The time between pulses

is also 5.5 hours (Atb). The following analysis is then possible using

the standard response charts.

R.,. ~ .. 1.0

4t

tLl - 1.25- 0.227

At 5.5

From charts , kh .A..R - 22

~ q

Ap - 0.15 psi

q - 3785 stb/d

B - 1.2 res bbl/stb q - 4542 res bbl/d

t'. - 0.5 cp

kh - 333 080

Assume h - 60 ft

k - 5.6 darcies

7

From charts • C6chr2 Ap .,. 2.4 x 10 -4

Atq

c - 13 x 10- 6 vol/vol/psi

r - 3493 ft

~t ~ 5.5 hrs - 330 minutes

; = 25.2%

First Inverse Response

Well A-6 was flowed at 7.30 pm on December 12. The (possible) maximum

negative response occurs at approximately 7.50pm, 0.33 hours later

(tL2). Then, as before

R = 1.0

~L2 = 0.33 - 0.061 At 5.5

From charts ' kh ~ - 64

P q

then k - 64 x 5.6

From Figure

then

22

16.3 darcies

QJ chr2 4p .,.

Atq

0.24 x 25.2%

2.4

-4 0.24 x 10

The apparent inverse pulse is therefore not consistent with

likely formation properties.

8

DISCUSSION OF RESULTS

The first positive response between W-l and W-6 is consistent with the

known typical properties of the sands in the West Kingfish field

(porosities typically 20%, permeabiltties typically 2-5 darcies). The

response is therefore of the right size, and occurs at the right time, to

be consistent with the known bulk formation properties.

The first inverse response is much less evident. The choice of the

"tangent point" is not obvious and the interpretation is subject to doubt.

Ideally in pulse tests a clear first response, first inverse response, I

second response etc should be observed. As a result, we cannot

conclusively interpret communication between wells W-l and W-6. However,

it is clear that a significant non-tidal pressure response has been caused

at W-l close to the time of shutting-in well W-6.

The test would have been improved if more time had been left between

commencing pressure recording and shut-in of well W-6, to observe the

tidal effects.

The results show no evidence of communication between W-l and W-19.

Ideally the test should have been continued for a little longer so that

the effects of two complete pulse shut-in periods could have been

observed.

9

CONCLUSIONS

1. A strong cyclical pressure effect. correlated to the tides at Eden.

NSW. is observed in the pulse testing of West Kingfish.

2. The effect is lagged by one hour from the expected tidal variation

at Eden. and has a tidal efficiency of 0.19 psi/m.

3. When the tidal effect is removed. a significant residual pressure

peak was observed at well W-6 shortly after shut-in of the West

Kingfish well W-l.

4. The cause of this peak 1'ls not known .. However. it is clear that it

is non-tidal. and is consistent with transmission of a pulse from

well W-l, ihdicating possible communication.

10

REFERENCES

1. DEPARTMENT OF DEFENCE (NAVY OFFICE), 1986 - Australian National Tide

Tables 1987, Australian Government Publishing Service, Canberra

2. HEMALA, M., 1985 - Tidal Effects in Jabiru Pressure Testing

(unpublished talk to SPE, Melbourne)

ACKNOWLEDGEMENTS

The assistance of Mr G. Morrison in preparing Figures 1-4 is appreciated.

Figure 1 was prepared by the BMR Drafting Office.

Date

12/12/87

13/12/87

11

TABLE 1

Tidal Maxima and Minima

WESTERNPORT

Standard

Time

0578

1106

1658

2246

0542

1134

1735

2319

Height (m)

2.7

0.9

2.4

0.7

2.7

0.9

2.4

0.8

EDEN

Standard

Time

0116

0613

1238

1949

0210

0723

1331

2031

NOTE: Pressure data are shown plotted against

summer time (not standard time)

Height

1.0

0.7

1.3

0.3

1.0

0.7

1.3

0.4

RESPONDING WELL

\ W-l "

38°35'

/ / /

/ / // /

./ °W-21

- -2250- Contour (metres be/ow see/evel)

12

Fig 1 West Kingfish development well locations

__ -0 W-16

IkJn I

A-21 0----__

A-2 ./ 0"

----­./---/

A-19/

°

Contour interval: 10m Datum: Sea level

14/OV/8

5

4

,-.. 0 "-ill f- 3 (/),-.. ,-,!Il

" W C f- 0 « !Il 0:: :J

0 3:.c Of-

2 -.1'-' l.o..

...J

(5

.. 0

3.2131

3.21305

.... I ~

3.213

~ 3.21295 w'" a:: VI ::>" VI r:

!3 ~ 3.2129 0:: :::I Il. 0

wt. 6 3.21285 I I ~ § 3.2128

ill

3.21275

3.2127

o

o

13

PULSE TEST W- 6& W-19 TO W-l

=

I I !

I 20 40

TIME (HOUR::;) o W-6 + W-19

PULSE TEST W-6 & W-19 TO W-1

I~

'\

\ AA 7 1\

-I ~ '\ ~

I

M 20

TIME (HOURS) PRESSURE AT W-1

\ 7 \J

40

Figure 2 Well flowrates and pressure response

60

!\

V '\

60

r--« (f)r--0.. CJ) '-./u

C W 0

3.2132

3.2131

3.213

n::: CJ) 3.2129 :J :J (f) 0 (f)£

wt.­n::: Cl..

3.2128

3.2127

3.2126

·DATA SHIFTED FORWARD 2iJ-.S3 I-lOURS

~

-++!t-~~~,

.~ V~ 1\ j\ ~ .r V ~

~

o· 20 40 60

TIME (HOURS) ORICII\JAL DATA -I- DATA FWD 24.53 HRS

Figure 3 Pressure response with data from 33 hours shifted forward 24.53 hours

DATA SHIFTED 24.52 HRS AND SUBTRACT

0.3

0.2 4J

~ 0.1

,...-.... -(f)

0.. '-...0'

W 0::: 0 ::) (f) (f) W 0:::

4J [D ]

~ ..."

~fHlQ, [jJ 1,-,

~ 71'RHl r.l ~ 1 NtH 1 IHtHWIH L.:.J '",", t.:U:.J

C

.... (.II

0..

-0.1

r!J

-0.2

-0.3

o 20 40 60

TIME (HOURS)

Figure 4 Pressure response without periodic effect

Ul n.. w rr ::J Ul Ul W rr n..

DATA SH IFTED 24.52 H RS Af\j D SU BTRACT

-O.2~~--4--+--~~--r--r~--4--+--+--+--r--r~--~~--+--+~

13 r 15

well W-6 shut in

17 19 21 23 25

1 . TIME (HOURS) 1 well W-6 flowed well W-6

shut in Figure 5 Pulse test analysis

27 29 31 33

PULSE TEST W-6 & VV-19 TO Vv-1 3.2131

3.21305· 2m

~ (/) 0.. ..

3.213 .--I ~ z

3.21295 1.5m Wr-... >-3 0:: III H

0 ::)"0 t'l (/) C

:I: (/) 0 3.2129 t'l W VI H ....

0:: ::::J Gl -...l

o..~ :I: >-3

w,s, . 3 ...J 3.21285 1m

0 I I

2 0 3.2128 1= 0 CO

3.21275 O.5m

3.2127 ~----------~~--------~----------~----------4-----------4-------~~

o 20 40 60

. TIM E (HOURS) PRESSURE AT W-1 + TIDE HEIGHT·

Figure 6 Pressure response and tidal effect

PRESSURE LESS TIDAL EFFECT

0.3

--0.2

(J) n.. .. 0.1 w o· z W 0::: W LL LL 0 0 w 0:::

~

i\ . r::J.t::k-. hI ,...." ~, I:::IPI'~ n ,.,., r ,.,.,

l~~ ) AF~ -l:::tt:jg'

:J Vl Vl -0.1 w a::: n..

-0.2

-0.3

o 20 40 60

TIM E (HOURS) o PRESSURE-TIDAL P

Figure 7 Pressure response without tidal effect