10. reservoir simulation-gassim
TRANSCRIPT
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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