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OH – ST - ET: Analysis of Dynamic Data in Shale Gas Reservoirs – Part 2
p 17/18
7 - Conclusion
In this study we have evaluated the different analysis techniques to find a suitable match for
our shale gas data and perform a reasonable forecast. The main results are summarized
below:
Linear flow
straight line
analysis
Material balance
PSS
Analytical MFHW
Numerical NL
Numerical NL
with desorption
Interferences
between fractures?
no
no
yes
yes
yes
Nonlinear PVT?
no
no
no
yes
yes
(all percentages express differences relative to the numerical NL with desorption case)
k (md)
--
No pss data
9.35E-05
(+30%)
7.20E-05
(0%)
7.20E-05
(--)
Xf (ft)
--
307
(+28%)
245
(+2%)
240
(--)
Nb. Fractures
--
42
(-2%)
43
(0%)
43
(--)
Xmf (ft)
12090*
(+17%)
12894
(+25%)
10535
(+2%)
10320
(--)
Lw (ft)
--
3900
(0%)
3900
(0%)
3900
(--)
Skin
0
2.7E-04
1.0E-03
1.0E-03
Drainage area after
10 yrs production
(ft
2
)
--
--
3.13E+06
(0%)
3.13E+06
(--)
STGIIP based on
above area (bscf)
--
--
6.70
(-18%)
8.20
(--)
Qg 10 yrs forecast
(bscf)
6.94
(+ 61%)
3.22
(-25%)
4.2
(-2%)
4.3
(--)
*based on k*X
mf
2
= 13670 md.ft
2
, assuming k = 9.35e-5 md
The equivalent single fracture straight line analysis will match the initial months of production,
but the response will inevitably deviate from that of a fractured horizontal well model after
some time. This is due to the neglect of interferences between fractures. It can however be
used as a method for finding an initial range of parameters of the analytical MFHW model.
In turn, the fractured horizontal well analytical model can correctly capture the interferences
between fractures, but its simplified PVT assumptions make it miss the actual problem of non
linearity induced by the gas properties - hence its pessimistic production forecast.
The nonlinear numerical fractured horizontal well model is not affected by those limitations. It
is the most reliable model in our study. Gas desorption played a minor role here, given that
our operating pressure is much higher than the Langmuir pressure.