Well Test Analysis

1

Chapter 11Estimating Average

Reservoir Pressure

Estimating

Average Reservoir Pressure

• We can determine average pressure either from:

– buildup test data

– or production (or drawdown) data

Buildup Methods

Well Test Analysis

2

Estimating

Average Reservoir Pressurefrom Buildup

• Middle Time Region Methods

– Matthews-Brons-Hazebroek (MBH) Method

– Ramey-Cobb Method

• Late Time Region Methods

– Modified Muskat Method

– Arps-Smith Method

Middle Time Region Methods

• Based on extrapolation and correction of MTR pressure trend

• Advantages

– Use only pressure data in the MTR

• Disadvantages

– Need accurate fluid property estimates

– Need to know drainage area shape, size, well location within drainage area

– May be somewhat computationally

involved

MBH Method

• Plot pws vs (tp+∆∆∆∆t)/∆∆∆∆t on semilog coordinates

• Extrapolate to (tp+∆∆∆∆t)/∆∆∆∆t=1 to find p*

• Calculate the dimensionless producing time

tpAD

• Using the appropriate MBH chart for the drainage area shape and well location, find pMBHD

• Calculate pavg

• If tp >> tpss, more accurate results may be

obtained by using tpss in place of tp in calculating the Horner time ratio and tpAD

Well Test Analysis

3

Ac

ktt

t

ppAD

φµ

0002637.0=

( )pADMBHD tpm

pp303.2

* −=

Matthews-Brons-Hazebroek Method

MBH Pressures For Square Drainage

Area

-1

0

1

2

3

4

5

6

0.01 0.1 1 10

tpAD

pM

BH

D

MBH Pressures For 2x1 Rectangle

-1

0

1

2

3

4

5

6

0.01 0.1 1 10

tpAD

pM

BH

D

Well Test Analysis

4

MBH Pressures For 4x1 Rectangle

-2

-1

0

1

2

3

4

5

0.01 0.1 1 10

tpAD

pM

BH

D

2400

2450

2500

2550

2600

2650

2700

2750

1101001000100001000001000000

Horner time ratio

Sh

uti

n w

ell

bo

re p

ress

ure

, p

sia

MBH Example - 2x1 Rectangle

p*=2689.4

m=26.7

MBH Method - Example

( )( )( )( )( )( )( )( )

35.0

3000150010615.125.015.0

4825.70002637.0

0002637.0

5

=

×=

=

−

Ac

ktt

t

ppAD

φµ

Well Test Analysis

5

-1

0

1

2

3

4

5

6

0.01 0.1 1 10

tpAD

pM

BH

D

MBH Example - 2x1 Rectangle

tpAD=0.35

pMBHD=2.05

MBH Method - Example

( )

( )

6.2665

05.2303.2

7.264.2689

303.2*

=

−=

−= pADMBHD tpm

pp

( ) 05.235.0 =MBHDp

For a well in the center of a 2x1 rectangle,

Matthews-Brons-HazebroekMethod

• Advantages

– Applies to wide variety of drainage area shapes, well locations

– Uses only data in the middle time region

– Can be used with both short and long producing times

• Disadvantages

– Have to know drainage area size, shape, well location

– Have to have accurate fluid property data