Abstract

Multi-phase flow modeling has the potential to illuminate the processes by which hydrocarbons are emplaced during secondary migration. We present an analytical and numerical model of two-phase flow to describe the relationship between secondary migration through fault zones and the concurrent charging of reservoirs in juxtaposition with these faults. The column heights that result from this process are controlled by the petrophysical properties of the fault zone, the flux of oil into the fault zone, and the geometry of the reservoir. At steady state, the capillary pressure between the fault zone and the adjacent reservoir must be equal; the capillary pressure (which is a function of the hydrocarbon saturation in the fault) at this interface determines the column height in the adjacent sand. Key results of the model are: 1) column height is a dynamic function of charge rate and not a static function of ‘capillary-entry pressure' as is often assumed, 2) a fault can serve both as a migration pathway and as a seal, 3) hydrocarbons are charged along faults and then backfill adjacent sands, 4) under-filled structures may result where reservoir sands pinch our away from the fault and hydrocarbons cannot displace the ‘perched' water that develops downdip, and 5) given similar petrophysical fault properties with depth and no permeability anisotropy, deeper sands will fill sequentially before shallower sands.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah