Geochemical comparison of reservoir solid bitumens with diverse origins

Geochemical and petrologic comparison of solid bitumens with various origins from reservoirs in Zaire, Canada and Kazakhstan were studied to provide insight into their formation processes and their physical and chemical properties. Results of this study can help develop methods for treatment and removal of solid bitumen, and evaluating producibility of associated hydrocarbon fluids. Characterization of these solid bitumens reveals a wide range in quantity and composition of extractables (soluble material) and in solid bitumen reflectance, which indicate significant differences in formation processes, hydrocarbon source and thermal maturity. The Zaire and Kazakhstan samples represent end members of the spectrum of solid bitumens studied. Solid bitumens from the Motoba Field, Zaire, are highly extractable and low in thermal maturity (0.2 – 0.3% bitumen reflectance). Reservoir mixing of a Cretaceous lacustrine sourced oil and a Tertiary marine sourced oil of different thermal maturities appears to be responsible for their formation. In contrast, 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 textures of the solid bitumens complement their geochemical characterization and provide insight into their origin. Solid bitumens from the Mitsue Field, Canada, which has been under miscible gas flood for sometime, are intermediate in the yields of extractables and thermal maturity ( 0.7% bitumen reflectance). The origin of the solid bitumen may have been gas deasphaltening originating from geological processes rather than from the recovery process. A combination of pyrolysis gas chromatography and petrology (bitumen reflectance and occurrence) provides distinction between production and geologically induced reservoir solid bitumen.