Summary
A number of vertically oriented heavy- and light-oil-depletion experiments
have been conducted in recent years in an attempt to investigate the effect of
gravitational forces on gas evolution during solution-gas drive. Although some
experimental results indirectly suggest the occurrence of gas migration during
these tests (especially at slow depletion rates), a major limitation of such an
interpretation is the difficulty in visualizing the process in reservoir-rock
samples. In contrast, experimental observations using transparent glass models
have proved invaluable in this context and provide a sound physical basis for
modeling gravitational gas migration in gas/oil systems. However, the
experimental observations often exhibit somewhat contradictory trends--some
studies showing dispersed gas migration, while others describe fingered,
channelized flow--and, to date, there appears to have been little systematic
effort toward modeling the wide range of behaviors seen in or inferred from
laboratory tests.
To this end, we present a new pore-network simulator that is capable of
modeling the time-dependent migration of growing gas structures. Multiple
pore-filling events are modeled dynamically with interface tracking allowing
the full range of migratory behaviors to be reproduced, including braided
migration (i.e., discontinuous flow of gas through narrow channels) and
discontinuous dispersed flow. Simulation results are compared with experiments
and are found to be in excellent agreement. Moreover, simulation results
clearly show that a number of network and fluid parameters interact in a rather
complex manner and, as a consequence, the competition between capillarity and
buoyancy produces different gas-evolution patterns during pressure depletion.
The implications of evolution regime on recovery from gas/oil systems
undergoing depressurization are discussed extensively.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
23 August 2008
- Meeting paper published:
21 October 2008
- Revised manuscript received:
26 November 2009
- Manuscript approved:
18 March 2010
- Published online:
5 August 2010
- Version of record:
2 December 2010
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