Abstract: Testing the Sensitivity of Hydrocarbon Migration and Overpressure Development to Rock, Fault, and Fluid Properties at the Field Scale

Christopher A. Shaw, Rob H. Lander

The coincident migration of hydrocarbons and maintenance of overpressure over geologic time is often considered to be problematic. Furthermore reservoirs with early overpressure development are typically given a low probability of receiving a hydrocarbon charge. We used a 2-D fluid-flow program to test the sensitivity of hydrocarbon migration and overpressure development at the field-scale to (1) stratal and fault-zone permeability, (2) fault geometry, and (3) hydrocarbon properties.

We studied two gas-condensate fields (one geopressure and one hydropressured) in southwestern Louisiana that produce from Miocene sediments in anticlinal structures bounded by large, listric fault complexes. An exploration prospect beneath the hydropressured gas-condensate field is expected to produce from the same interval as the geopressured field. Fluid-flow models calculated fault-related migration, reservoir charge, and overpressure development.

Sensitivity analyses show that (1) permeabilities that maintain observed overpressures allow gas migration but prohibit oil migration, (2) reservoirs become overpressured shortly after deposition, (3) overpressure inhibit mechanical compaction and, therefore, affect estimates of burial history and permeability, (4) hydrocarbon migration, unlike overpressure, is sensitive to fault-zone geometry, and (5) both overpressure and hydrocarbon migration are strongly influenced by fault-zone permeability. Results indicate that migration along the fault-plane does not significantly deplete overpressures, and that existing reservoirs were overpressured at the time of migration

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994