ABSTRACT: Petroleum Geology of Heavy Oil in the Oriente Basin of Ecuador: Exploration and Exploitation Challenge for the 1990s

Roy H. Leadholm

Published Ecuadorian government forecasts suggest that Oriente basin light oil (21-32° API) production may start to decline in the early to mid-1990s. To maintain stabilized production into the next century, heavy oil reserves (10-20° API) will have to be aggressively exploited. The Oriente's undeveloped proven plus probable heavy reserves are substantial and are expected to exceed 0.5 billion bbl.

A recent discovery made by Conoco Ecuador Ltd., operator of Block 16 for a group which consists of O.P.I.C., Maxus, Nomeco, Murphy and Canam, is a good model for future exploration and exploitation of heavy oil in the remote eastern regions of the basin. Amo-1 tested a low-relief anticline (less than 100 ft vertical closure) and encountered 10-20° API oil in five Cretaceous sandstone reservoirs (8000-10000 ft depth). Cumulative test production was 1062 BOPD. Subsequent drilling along the trend resulted in three additional discoveries.

The Cretaceous sands were transported from the Brazilian shield by the westward flowing proto-Amazon River and were deposited in fluviodeltaic, tidal, and high-energy marginal marine environments. Air permeabilities are high with geometric mean values approaching several darcies. Porosities average 18-22% in generally well-consolidated sands. The heavy oils are the result of mild biodegradation and/or expulsion from a thermally immature source. Oil-to-oil correlations suggest that all of the basin oils have the same or similar origin, probably marine calcareous shales of the Cretaceous Napo formation.

The Block 16 project will provide a major step toward the strategic exploitation of the Oriente basin's heavy oil reserves, when it comes on stream in the early 1990s.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990