4d Semilog Analysis for Oil Wells-1

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Semilog AnalysisFor Oil Wells



Semilog Analysis

Instructional Objectives

1. Analyze constant-rate drawdown

2. Analyze buildup



Ei-Function Solution

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¨ JQ

Q! kt

r c948Eikh

qB

6.70pp

2t

i



Reservoir Pressure Profile

500

1000

1500

2000

1 10 100 1000 10000

Distance from center of wellbore, ft

P r e s s u r e , p s

i

s = +5

s = -2

s = 0



Incorporating Skin into the

Ei-Function Solution

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kt

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kh

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s2kt

r c948Eikh

qB6.70pp

2t

i

2

wti

For r = r w

For r > r a



Log Approximation to the

Ei-Function

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qB6.162pp

2wt

1010iwf

bmxy !



Estimating Permeability and Skin

mh

qB6.162k

Q!

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JQ

! 23.3

r c

klog

m

pp151.1s

2wt10

hr 1i



Drawdown Test Graph

700

800

900

1000

1100

1200

0.1 1 10 100 1000

Elapsed Test Time, hrs

P r e s s u r e , p s i

(t2, pwf2)

(t1, pwf1)



Exercise 1

Determining permeability and skin factor

from a constant-rate flow test



Exercise 1

3300

3350

3400

3450

3500

3550

3600

1 10 100

Time, hrs




Problems with Drawdown Tests

It is difficult to produce a well at a

strictly constant rate

Even small variations in rate distort thepressure response

There is one rate that is easy to maintain

± A flow rate of zero. A buildup test is conducted by shutting

in a producing well and measuring the

resulting pressure response.



Buildup Test - Rate History

(t0

- q

0 tp + (t

q

tp (t0

q



Buildup Test - Pressure Response

(ttp

(t0

tp + (t

0



Buildup Test - Superposition

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s869.023.3r c

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qB6.162

s869.023.3

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klogttlog

kh

qB6.162pp

2wt

1010

2

wt

10p10iws



Buildup Test

Straight Line Analogy

hmqB6.162k Q!

1t

tt@bp pi !

(

(!



Buildup Test Graph

1400

1500

1600

1700

1800

1900

2000

110100100010000

Horner time ratio


pi



Horner Pseudoproducing Time

last

ppq

N24t !



Exercise 2

Determining permeability and reservoir

pressure from buildup tests



2500

2550

2600

2650

2700

2750

2800

1101001000

Horner Time Ratio

P r e s s u r e , p

s i

Exercise 2

4d Semilog Analysis for Oil Wells-1

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