DECKER, C. L., H. YUAN, J. S. WATKINS, and Y. LI, Department of Geology and Geophysics, Texas A&M University, College Station, TX

Abstract: Multiphase Hydrocarbon Migration and Entrapment in Fault-Bounded Reservoirs

The processes of migration and entrapment of multiphase hydrocarbons are poorly known. Key issues include (a) estimating reasonable rates of charge under geologic conditions; (b) the effect of varying GOR on hydrocarbon retention in the reservoir, and the distribution of trapped oil vs. gas; and (c) the effect of fault permeability.

To gain insight into the above issues, we have used off-the-shelf reservoir simulation software to examine simultaneous migration of oil and gas through a series of stacked permeable reservoirs separated by impermeable shale and bounded by faults. Appropriate fluid, reservoir, and fault properties are based on data collected from a field with similar reservoir geometry.

Our results suggest that the total time to fully charge all reservoirs is less than 20,000 years under most conditions, given a sufficient source. For our model, this is comparable to a flow rate on the order of tens to hundreds of mcf/day.

At low GORs, hydrocarbons are segregated into gas-charged and oil-charged reservoirs. At higher GORs, hydrocarbons are more evenly distributed, but even at very high GORs, maximum gas saturation is not achieved.

There is a threshold permeability above which fault behavior changes dramatically from conduit to barrier; preliminary results indicate that the threshold value depends on hydrocarbon type.

Modeled distribution of hydrocarbons is similar to that observed in a field currently undergoing active charge. 

AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana