Relationship between reservoir bitumen and hydrocarbon migration in Dabei region, Kuqa Foreland Basin

Based on systematic analyses of microscopic characteristics, thermal maturation and biomarker compounds of reservoir bitumen, it was discussed in this paper the bitumen origin as well as the hydrocarbon migration and accumulation in Dabei region of the Kuqa Foreland Basin. A little black resin bitumen was observed in microscopic fractures of sandstone reservoir under salt bed of the Kumugeliemu Group in Dabei region. 2 groups of bitumen were found in well Dabei202, with reflectivity of 1.07% and 0.47%. 1 group of bitumen was found in well Tubei1, with reflectivity of 0.43%, and its content was very rare. Solid bitumen in reservoir was the result of mixed precipitation of oil and gas of different origin and stage. Therefore, natural gas in Dabei region is not originated from crude oil cracking. At least 3 stages of hydrocarbon charging took place in under-salt traps such as Dabei1 and Dabei2. Crude oil in ancient reservoir migrated into shallow sandstone along the Kelasu thrust fault in the north, and then accumulated in the Dawanqi anticline. Reservoir bitumen was found in well Tubei1 near the Kelasu thrust fault, indicating that sandstone worked as the pathway for hydrocarbon migration. Hydrocarbon might accumulate in the higher part of the fault block. The research illustrated the origin of natural gas in the Kelasu structural belt, and might guide ancient reservoir exploration in the region.