Datapages, Inc.Print this page

Abstract: Chemical and Isotopic Studies of Oil Field Waters and Gases: Elk Hills Region, CA


Waters, oils and gases were sampled from NPR#1 (Bechtel) and the adjoining Cymric-McKittrick Field (Chevron) and the North Coles Levee Field (Arco). Water compositions are generally consistent with a diagenetically altered seawater combined with dilute meteoric water. Stevens and deeper fluids are generally Na-enriched at the expense of Ca which may suggest dissolution by organic acids. The exceptions are the Ca- and Br-enriched waters of the Shallow Oil Zone. Br concentrations show a general decrease deeper in the fields. The Shallow Oil Zone and the deeper Point of Rocks/Phacoides waters establish two endmembers with most samples confined to a rapidly changing mixing zone within the Miocene Stevens (NPR#1) and the Antelope (Cymric) Formations. The Br enrichments may be the results of (1) seawater evaporated to halite precipitation followed by dilution, (2) membrane filtration, or (3) a chemical affinity between Br and organics like that observed for I.

Rare gas measurements show the highest Xe enrichments ever measured in natural fluids. Xe enrichments dominate the gases of the Shallow Oil Zone and decrease deeper in the section along a mixing line with a typical air saturated water of the Phacoides/Pt of Rocks. There is also a three component mixing relation for F{Xe} vs. F{He} among the Shallow Oil Zone (high F{Xe}), the Antelope Shale (high F{He}) and the Phacoides/Pt of Rocks (low F{Xe} and F{He}). The Antelope Shale samples suggest a U-rich shale member. The Phacoides/Pt of Rocks samples contain a component of mantel He.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California