Abstract: Oil Migration Along Faults: Example from L and K Fields, Offshore NW Java PSC, Indonesia

Thomas L. Phillips

Hydrocarbons in the subsurface are impelled by three major forces: a downward-directed gravitational force, forces due to pressure gradients (buoyant and hydrodynamic), and a capillary force which opposes hydrocarbon entry into water-wet rocks. The speed and direction of hydrocarbon movement is the resultant of these force vectors. Burial rates and temperature determine the rate of expulsion from source rocks into carrier beds. Migration in carrier beds can be described by Darcy's flow law. When a carrier bed is intersected by an open fracture of fault with permeable gouge, some or all of the flow may be diverted up the fault. Flow proceeds up the fault until a carrier bed is encountered intersecting the fault. If the hydrocarbon column of the oil in the fault exerts enough pressure t exceed the displacement pressure of the carrier bed, and if the carrier bed dips up from the fault and thus offers a positive migration potential gradient, then part of the flow will be diverted into the carrier bed. Flow will be apportioned between the carrier bed and the ongoing fault according to the relative flow rates which may be accommodated in the two systems. Flow will proceed up the fault until another carrier bed is encountered and the flow stream again splits. In this fashion a fault may distribute hydrocarbons to multiple reservoirs. These migration principles were applied in an analysis of the hydrocarbon distribution in the L and K Fields of the southern Ardjuna sub-basin, which is a Tertiary basin located north of the island of Java. The basin lies within the Offshore No thwest Java PSC held by ARCO Indonesia and partners. Migration principles explain the observed oil-in-place in the 15 stacked reservoir sands of the L Field and the 7 reservoir sands of the K Field.

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