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VA – GP - OA: Numerical Multiphase PTA
p 16/29
Figure 20: Influence of Sgr on oscillations during production phase (R=50,000 ft, k=100 mD)
3.3. Analysis of multiphase processes during drawdowns and build ups
Drawdown analysis
Figure 21 shows the evolution of the pressure derivative during the production when R=50,000
ft, for three different values of the permeability. Although oscillations are present, we can
observe a global increase of the derivative during the depletion. This corresponds to a
decrease of the total mobility while gas saturation appears and increases in the reservoir.
Figure
21: Evolution of the pressure derivative during production phase (R=50,000ft)
This is partly explained by the non-linearity of the total mobility curve, as previously explained
in section 1.2. When gas appears in the medium, the total mobility decreases until the gas
saturation reaches a certain value. Note that if one assumes constant viscosities, the mobility
decrease is entirely due to the decrease of the relative permeabilities when gas appears in the
medium (figure 22).
0.01
0.1
1
10
100
1000
10000
Time [hr]
100
1000
Pressure [psi]
Sgr = 0.1
Sgr = 0
0.01 0.1
1
10
100 1000 10000 1E+5 1E+6
Time [hr]
10
100
1000
10000
K=200mD
K=100mD
K=50mD