Compaction of Unconsolidated Oil Sands: Pilot Study in Orinoco Oil Belt

Marcel Chin-A-Lien, Carlos Porras, Jochheim Uwe

The Orinoco belt is a giant heavy oil accumulation whose hydrocarbons are trapped in highly porous unconsolidated sands of the Miocene Oficina Formation. When submitted to production, compaction of these loose reservoir sands is triggered by the decline of reservoir pressure, an important mechanism of primary oil recovery.

A pilot project is being conducted in the Hamaca area to investigate this phenomenon and to quantify its impact on oil recovery. The test consists of 13 steam injectors-producers and two observation wells. These were extensively cored and logged implementing the Hydrolift coring technique and placing 72 radioactive bullets for compaction monitoring. The main U_2-3 reservoir under study is 110 ft thick. It consists of multistoried, fining-upward, medium to coarse-grained, cross-bedded, mature to submature quartzarenites deposited by a high-energy distributary-channel complex which prograded northwestward on a Precambrian basement. Porosities and permeabilities are on the order of 30% and 4 darcys, respectively; clay content is low, oil saturation averages 90%, and the crude A I gravity is approximately 10°.

The project is generating precise long-term data related to the positive effect of reservoir compaction on production. These data are used to validate a production-compaction simulator and to forecast reservoir and production behavior in the rest to the Hamaca area. A preliminary evaluation indicates that reservoir compaction reduces a substantial amount of the initial pore volume and contributes to high primary recovery efficiencies.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.