Sakhalin Island Hydrocarbon Source Potential of Miocene and Oligocene Siliceous Rocks

Commonwealth of Independent States

In 1993 Core Laboratories completed a regional geochemical study of mostly Miocene clastic source rocks in the Sakhalin area. Oil companies participating in this first study requested that Core Lab develop a similar study which primarily focuses on Oligocene siliceous rocks in the same area.

The Oligocene Pilengsk, a siliceous shale, is known to be a source rock for oil accumulations in the Okruzhnoye field where oil is produced from within fractures. A regional geochemistry study of the Oligocene Pilengsk and its equivalents will help determine the extent of this fractured shale play throughout the Sakhalin area.

The contribution of oil from Oligocene source rocks to Miocene and younger reservoirs will also be examined. Results can be used to develop plays based on the migration pathways between Oligocene source rocks and younger reservoirs.

The study objective is to characterize the regional hydrocarbon source potential of Oligocene siliceous rocks and to determine where in the Sakhalin area Oligocene source rocks are effective, that is where Oligocene source rocks have contributed hydrocarbons to petroleum accumulations.

Core Lab has obtained regional coverage of 100 mostly Oligocene source rock samples from seventeen (17) subsurface (well) and two outcrop locations. The sample suite also includes the Middle/Lower Miocene Pilsk formation which is a locally developed siliceous shale in the northern Sakhalin area. Crude oil samples were collected from eight (8) locations in the study area including both Oligocene and younger reservoirs.

The results of this study are presented in this interpretive report as well as in analytical data volumes. This report provides an interpretation of the extensive geochemical database generated by Core Laboratories for this study. Maps, tables, and graphical displays of geochemical data are included in this interpretive report. The bulk of the analytical data is presented in the Oil and Rock Data Volumes.