Page 133 - Principles of Applied Reservoir Simulation 2E

118 Principles of Applied Reservoir Simulation

influx for a system with an irreducible gas saturation (Sgr) of 0%. The change
in gas saturation shows the influx of aquifer water. The change in fluid content
changes fluid bulk modulus. As a consequence, the ratio V pIV s changes
significantly in the waterflooded part of the reservoir.
If we rerun the example with an irreducible gas saturation of three percent,
we obtain the results shown in Figure 12-8. The large change in V pIV s is no

Aquifer Influx at 1 Year
Sgr = 3%

10
WINB4D Block Index

Figure 12-8. Reservoir performance with Sgr = 3%.
longer observed because the presence of a small amount of gas significantly
changed the compressibility of the system.
Time-lapse seismic tomography, or 4-D seismic, could be used in our
hypothetical example to track the movement of invading aquifer water, but the
presence of a small amount of gas in the invaded zone increases the difficulty
of detecting the gas-water contact. Calculations of 4-D seismic performance
based on algorithms like the one coded in WINB4D can predict 4-D seismic
responses [Fanchi, 1999], but such algorithms are not yet widely available in
commercial simulators.
Although it is risky to predict technological developments, it is possible
to infer trends by extrapolating ongoing research activities in the industry.
Thakur [1996], for example, wrote that data management and the integration