Petroleum Generation in the Nonmarine Qingshankou Formation (Lower Cretaceous), Songliao Basin, China

Abstract

The Songliao basin, covering an area of 260 000 km2 in northeast China, is known as one of the world’s most prolific oil- and gas-producing basins. The super giant Daqing oil field is located in the center of the basin with major oil plays in the Lower Cretaceous Yaojia and Qingshankou Formations. The nonmarine Qingshankou Formation also acts a primary source for the basin’s hydrocarbon reserves. Dark lacustrine mudstones with a thickness of between 300 and 400 m are widely distributed in the basin. The Qingshankou Fm. kerogens range from sapropelic to gas-prone. The average organic carbon and total hydrocarbon contents are 2.3 wt.% and 1540 ppm, respectively. The generated crude oils display many typically lacustrine oil characteristics including high wax contents, high nickel/vanadium ratios, low sulfur contents, and light carbon isotopic compositions. The Gulong depression, west of the Daqing anticlinal belt, was a primary depocenter for the Qingshankou Fm. Here, the unit covers approximately 50 000 km2 and is currently buried to depths of 1900 to 2400 m. The hydrocarbon reserves associated with Qingshankou Fm. can be attributed to the interrelationship among the source-reservoir-seal system which includes encapsulating lacustrine mudstones, and lenticular delta-front and channel filled sand bodies. Recent drilling has indicated that substantial Qingshankou-derived oil remains to be produced.