Computer Simulation of Pore-Pressure Anomalies as an Aid to Exploration for Lenticular Reservoirs in Mature Basins

Ben Rostron, Jozsef Toth

Lenticular reservoirs are accompanied by diagnostic pore-pressure anomalies when situated in a field of formation-fluid flow. Computer simulations have shown that these anomalies depend on the size and shape of the lens, the direction and intensity of flow, and the hydraulic conductivity contrast between the lens and the surrounding rock. Furthermore, the anomalies reflect the position of the petroleum-saturated portion of a lens since hydraulic conductivity is related to hydrocarbon content.

Studies to date have shown that for an oil-free lens a pair of oppositely directed, symmetrical pressure anomalies exists. Each pair consists of a positive and a negative anomaly, respectively, at the downstream and upstream ends of the lens. A 2,000-m long lens could generate a 200-kPa anomaly in a commonly occurring gravity-flow field. A lens that is filled with hydrocarbons will create a lower conductivity reservoir thus causing negative anomalies at the downstream and positive anomalies at the upstream ends of the lens. The "paired" anomaly for a partially full lens falls in between these two end members.

Pore-pressure distributions from drill-stem tests in mature, well-explored regions can be compared to computer-simulated pore-pressure anomaly patterns. Results can be interpreted in terms of the lens geometry and degree of hydrocarbon saturation.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.