Geochemical characterization of solid bitumen (migrabitumen) in the Jurassic sandstone reservoir of the Tut Field, Shushan Basin, northern Western Desert of Egypt

Asphaltene-rich solid bitumen was identified within the pore spaces of the Middle Jurassic Khatatba sandstone reservoir in the Tut Field, Shoushan Basin, Egypt. Despite good reservoir properties have been detected, the solid bitumen forms barriers in the reservoir, which prevents economic petroleum production. Petrographical and organic geochemical techniques were applied in order to characterize the source rock of the bitumen and its formation mechanisms. Organic geochemical results confirm the presence of actively migrating non-biodegraded hydrocarbons within the Khatatba sandstones. Biomarker data suggest that the solid bitumen originated from a marine shale source rock that was deposited in mildly anoxic to suboxic conditions. Biomarker oil-source rock correlation with the organic-rich sediments of the Khatatba Formation indicates that the shale and coaly shale within the Khatatba Formation are an effective source rock in the area. The natural deasphalting is the predominant mechanism for the formation of the asphaltene rich solid bitumen in the Khatatba sandstones. Adsorption of asphaltenes onto authigenic kaolinite played a major role in the fixation of bitumen. Furthermore, gas deasphalting caused by gas injection may have contributed to a phase change in the reservoir fluid and deposition of solid bitumen. The injected gas is generated from Khatatba Type III kerogen or older source rocks in the Shoushan Basin during the mature stage of hydrocarbon generation. (c) 2012 Elsevier B.V. All rights reserved.