Comparison of Onshore and Offshore Petroleum Systems in the Central Caspian Region

Michael A. Abrams¹ and Ger W. van Graas^2
1EGI, University of Utah, Salt Lake City, UT
²Global Exploration, Statoil, Stavanger, Norway

The Central Caspian region is bounded by the Karpinsky Ridge-Karatau Uplift to the north and the Absheron Sill to the south. Until recently, petroleum exploration was limited to the onshore areas and several discoveries have been made both in Russia (Terek-Caspian Foredeep) and in Kazakhstan (Mangyshlak Basin).

Geochemical analysis of oil, condensate, gas and source rock samples reveals the presence of several petroleum systems in the onshore areas, representing a range of depositional environments. Some of these are linked to Triassic lacustrine source rocks that were deposited in a synrift setting, while others are younger and more marine in nature. The lacustrine-sourced oils display variations with regard to salinity and organic matter facies.

Recent exploration in the offshore Central Caspian has led to the discovery of several fields containing variable amounts of oil, condensate and gas. Geochemical analysis of oils and condensates from these offshore discoveries indicates that their origin is different from the onshore petroleum system. Most of the offshore fluids appear to be from a marine source facies, not seen in the onshore. The offshore condensates are derived from the same source rock as the oils and do not appear to be a product of high maturity of the source rock. The gasoline-range hydrocarbon fraction and observations from seismic and reservoir distribution data indicate that the oil and gas-condensate distribution is related to source rock character and phase separation.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas