Geochemical comparison of reservoir solid bitumens with diverse origins

Geochemical and petrologic comparison of solid bitumens with various origin s from reservoirs in Zaire, Canada and Kazakhstan were studied to provide i nsight into their formation processes and their physical and chemical prope rties. Results of this study can help develop methods for treatment and rem oval of solid bitumen, and evaluating producibility of associated hydrocarb on fluids. Characterization of these solid bitumens reveals a wide range in quantity and composition of extractables (soluble material) and in solid b itumen reflectance, which indicate significant differences in formation pro cesses, hydrocarbon source and thermal maturity. The Zaire and Kazakhstan s amples represent end members of the spectrum of solid bitumens studied. Sol id bitumens from the Motoba Field, Zaire, are highly extractable and low in thermal maturity (0.2-0.3% bitumen reflectance). Reservoir mixing of a Cre taceous lacustrine sourced oil and a Tertiary marine sourced oil of differe nt thermal maturities appears to be responsible for their formation. In con trast, solid bitumens from the Tengiz Field, Kazakhstan, are characterized by their extremely low extractables, high bitumen reflectance (>1%)and low atomic H/C ratios(< 1.0). Thermal alteration is an important process in the formation of these highly mature bitumens (pyrobitumen). Petrographic text ures of the solid bitumens complement their geochemical characterization an d provide insight into their origin. Solid bitumens from the Mitsue Field, Canada, which has been under miscible gas flood for sometime, are intermedi ate in the yields of extractables and thermal maturity (similar to 0.7% bit umen reflectance). The origin of the solid bitumen may have been gas deasph altening originating from geological processes rather than from the recover y process. A combination of pyrolysis gas chromatography and petrology (bit umen reflectance and occurrence) provides distinction between production an d geologically induced reservoir solid bitumen. (C) 1998 Published by Elsev ier Science Ltd. All rights reserved.