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OH – ET – VA - LL: Analysis of Dynamic Data in Shale Gas Reservoirs – Part 1 – Version 2 (December 2010)
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9 – Fractured horizontal well and no desorption
We now proceed from the single equivalent vertical fracture to our real fractured horizontal
well model, carrying on the same parameters described in §3: 10 infinite conductivity fractures
with X
f
=200 ft each, only the fractures are flowing (flow to the horizontal well drain is not
considered), all fractures are fully penetrating.
The comparison between the equivalent single fracture run and the multiple fracture run is
shown below for the four first years of production.
Note: we are in Topaze here, the “time” used is the material balance time (cumulative
production divided by instantaneous rate). As the rate declines, a production of 4 years will
correspond to more than two thousand days on the material balance time scale. Nothing to
worry about...
We see that after a couple of months the fractured horizontal well deviates from the single
equivalent fracture case. The overall productivity of the fractured horizontal well becomes
better.
Physical explanation: At early time the flow is strictly linear, orthogonal to the fracture planes.
However after a while the flow widens beyond the fracture extent and more production starts
coming from the tip. This additional production improves the productivity of the system and
the pressure / derivative response starts to bend down. When we have a single fracture we
have only two fracture tips. When we have ten fractures this makes it 20. Needless to say that
the productivity of the fractured horizontal well, at this stage, becomes better than the single
equivalent fracture.