Geology of Shale Oil and Potential Shale Oil Reservoirs in the Lower Part of the Green River Formation, Uinta, Piceance and Greater Green River Basins

Abstract

There is renewed interest in the shale oil potential of lacustrine rocks because of the recent successful development of a shale oil play in the informal Uteland Butte member of the lacustrine Paleocene and Eocene Green River Formation in the Uinta Basin, Utah using modern horizontal drilling and fracking techniques. The Green River Formation was deposited in large lakes in three intermontane basins in the western interior of the U.S., the Piceance, Uinta, and Greater Green River Basins. These three basins contain the world's largest in-place oil shale resources with recent estimates of 1.53 trillion, 1.33 trillion, and 1.44 trillion barrels of oil in place in the Piceance, Uinta, and Greater Green River Basins respectively. The Uteland Butte member was deposited in an early freshwater stage of the lake in the Uinta Basin and is a successful shale oil play because it is thermally mature for hydrocarbon generation and contains both organic-rich shale and brittle carbonate rocks. Abnormally high pressures in the “sweet spot” for the Uteland Butte are also important for production. Variations in organic richness of the Uteland Butte were studied using Fischer assay analysis used in the oil shale assessments, and formation pressures were studied using drill-stem tests. Freshwater lacustrine rocks similar to the Uteland Butte member are present in the Piceance and Greater Green River Basins, but these intervals are marginally mature to immature for hydrocarbon generation and contain far less carbonate rocks than the Uteland Butte. Burial histories of the three basins were reconstructed using isopach and structure contour maps. After deposition of the lacustrine interval, rates of subsidence increased in the Uinta Basin and decreased in the Piceance and Greater Green River Basins, thus creating the thermal maturity necessary for a major petroleum system in only the Uinta Basin.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015