Detailed Geochemical Evaluation of Green River Shale Core: Implications for an Unconventional Source of Hydrocarbons
Brian Jarvie, Daniel Jarvie, Tim Ruble, Hossein Alimi, and Valentina Baum
Humble Geochemical Services, Humble, TX
The Green River oil shale is a large, unconventional natural resource. In the 1970-80's a large effort was undertaken to develop the Eocene Green River Shale oil-shale resources in the U.S.A., but low oil prices and high retorting costs rendered the resource uneconomic. The impact of the rock matrix on the decomposition rates, product yield, and type of products that could be generated during oil-shale retorting was demonstrated by Lawrence Livermore National Laboratory, but not its highly variable geochemical characteristics. Detailed geochemical analyses of the Green River Shale were performed on a full core of the Lower Green River Formation (1200 ft.) taken from Chevron Marsing #16 well drilled in Wasatch County, Utah in the southwestern Uinta Basin. Basic TOC and Rock-Eval analysis demonstrated that the petroleum yields varied from 1 to 5492 bo/af with an average value of 673 bo/af. The marginal lacustrine mud flat zone had an average petroleum potential of 1169 bo/af, whereas the distal deltaic zone averages 182 bo/af, and two different carbonate zones average 340 and 641 bo/af. Although being low thermal maturity (ca. 0.50%VRo), rock extracts fingerprints and paraffin envelopes as well as peak ratios showed considerable variation. Pristane-to-phytane ratios vary from 0.50 to 1.75. Paraffin profiles are variable ranging from unimodal to trimodal distributions indicative of difference in organic matter. Sandy intervals were much less complicated having a unimodal, primarily n-paraffin distribution. In the marginal lacustrine sequence the b-carotane yields showed inverse correlation to oxygen indices. These geochemical variations impact development of this resource.