10. Reservoir Simulation-Gassim

7/28/2019 10. Reservoir Simulation-Gassim

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Reservoir Simulation -

Gassim


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Gassim

From textbook Gas Reservoir

Engineering by Lee and Wattenbarger

VBA program in Excel

Intended for student usage

Analytical, numerical,

transformation methods


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Gassim

1D or 2D

Cartesian or radial grid

Single phase gas or liquid


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Data organization

Single section

Grid section

Schedule section

(each section ends with END)


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Single section

Each data has one value (except CNST)

Specifies:

Grid size

Reservoir temperature, reference pressure

Gas gravity, Sw, cf, cw Whether radial coordinates

Whether liquid (with Bo, o)

Specifies certain run controls:

Matrix methods

Newton iterations


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Example of Single DataCMNT

CMNT Homogeneous Cylindrical Reservoir

CMNT Radial Flow, Constant-rate production, Infinite-acting

CMNT Slightly Compressible Fluid

CMNT

CMNT

CMNT Single Value Input Data

IMAX 20JMAX 1

RWEL 0.5 (radial coordinates)CROC 0.000015

PREF 3000

NEWT 1

BETA 0

CMNT Bo, rcf/scf mo, cp

CNST 1.475 0.72 (liquid case)ENDCMNT Grid Input Data

.

.

.END

CMNT Schedule Data

..

.

END


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Grid Section

Specifies data for each gridblock Specifies grid dimensions

2D (DELX, DELY and H)

radial (RR, DELY)

Grid data:

permeability porosity

thickness

initial pressure


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Example of cartesian grid

IMAX 10

JMAX 5

RWEL 0.5

.

.

.

END

DELX 110

DELY 150

H 30

.

.

.

END

CMNT Schedule Data.

.

.

END

1 2 3 4 5 6 7 8 9 10

1

2

3

4

5

I =

J =


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Example of radial grid

IMAX 10

JMAX 2

RWEL 0.5

.

.

.

END

RR -1

0.77 1.19 1.84 2.84 4.40

6.79 10.50 16.22 25.06 38.7

DELY 150

.

.

.

ENDCMNT Schedule Data

.

.

.

END

-1 indicates that an

array follows.

Otherwise a constant

value is used


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Schedule Section Controls well specifications

location (NAME)

constant rate (QG)

contant pwf(PWF) Controls time schedule output

1 means output at TIME output

2 means output each timestep Controls timesteps (DELT, ALPH, DTMX)


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Schedule example

NAME 1 3 5 0

QG 1 12000

TIME 365

END

Well 1 is located at I = 3, j = 5 and produces at aconstant rate of 12,000 scf/day for 365 days


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Schedule example

NAME 2 6 8 0

PWF 2 1500

TIME 730

END

Well 2 is located at I = 6, j = 8 and produces at a

constant BHP of 1500 psia for 730 days


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Schedule example

NAME 1 3 5 0

NAME 2 6 8 0

QG 1 12000

TIME 365

PWF 2 1500TIME 730

END

Well 1 produces at a

constant rate of 12,000

scf/day for 730 days.Well 2 produces at

constant BHP after 365

days until 730 days.


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Schedule Section programming

logic When a TIME data line is read, the

simulator executes the timesteps

required to reach that timethen ---- it reads the data to the

next TIME data line


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Timestep control

DELT sets the first t for the time

period

ALPH sets t equal to ALPH timethe previous timesteps t (after the

first timestep in the period)

DTMX sets a maximum value fort


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Timestep example

DELT 1

ALPH 1.5

DTMX 10

TIME 60

The timestepsequence is

1

1.5

2.25

3.375

5.06

7.59

10

10

10

10


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Timestep control

Well conditions (QO or PWF) change

after a TIME data line, a small DELT

should be included so the new

rate/pressure conditions start withsmall timesteps

DELT 1

ALPH 1.5

NAME 1 3 5 0

NAME 2 6 8 0

QG 1 12000

TIME 365

DELT 1PWF 2 1500

TIME 730

END

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10. Reservoir Simulation-Gassim