--> ABSTRACT: The Petroleum Geochemical Risk Associated with the Hydrocarbon Prospectivity for the Paleozoic Succession, Northern Middle East, by G. A. Cole and B. Wygrala; #91021 (2010)

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The Petroleum Geochemical Risk Associated with the Hydrocarbon Prospectivity for the Paleozoic Succession, Northern Middle East

COLE, GARY A., and BJORN WYGRALA

The Paleozoic basins of the northern Middle East have been explored with limited success. A series of wells in Jordan found small accumulations of oil at Wadi Sirhan and gas at Risha, and wells in the Nafud basin in Saudi Arabia yielded no commercial accumulations of hydrocarbons, but gas was found in several wells. No wells in western Iraq have targeted the Paleozoic succession, so this remains an unexplored area. The Euphrates graben of Syria also has Paleozoic potential as some of its hydrocarbons have been attributed to the basal Silurian source rock.

The Paleozoic succession of the northern Middle East contains a single, primary source rock, the gamma-ray hot shales located at the base of the Silurian section. This unit was deposited under sediment starved, marine conditions during the maximum transgression following the Late Ordovician glaciation. These hot shales are organic-rich, oil-prone, and range in thickness from 10-175 feet (3-53 m). Along the basin margin of Saudi Arabia and Jordan, these marine shales are immature and contain from 2 to 5 percent TOC on average, but some intervals exceed 15 percent TOC. Hydrogen indices average between 500 and 600 mg HC/g TOC making this a prolific oil source.

The deep burial, large areal unconformities, and migration history appears to be responsible for why a large portion of the northern Middle East is not prospective for hydrocarbons. A series of 1-D and 2-D models have indicated that the Silurian basal hot shales in the Nafud basin expelled most of their oil charge during the Paleozoic burial (Nafud basin) and only gas potential remains. However, in other parts of the northern Middle East such as Syria or northern Iraq, hydrocarbon prospectivity becomes more favorable due to the different burial histories. The modeling results, therefore, can be used to assess geochemical risk across the northern Middle East.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.