Differential petroleum charging controlled by movements of two strike-slip faults in the Shunbei area, Tarim Basin, northwestern China

Recently, considerable hydrocarbon reserves have been discov-ered in Lower-Middle Ordovician carbonate reservoirs situatedsurrounding two conjugate strike-slip fault zones in the Shunbeioilfield, Tarim Basin, northwestern China. Through the inte-grated analysis of crude oil physical properties, geochemicalcompositions, andfluid inclusions, the differential petroleumcharging history of the Shunbei oilfield has been investigated.For the Shunbei (SHB)5 fault zone, two discrete ranges ofhomogenization temperature of coeval aqueous inclusions indi-cate intense charging during the early Yanshan Orogeny, withminor charging during the late Himalayan Orogeny. For theSHB1 fault zone, the extended homogenization temperaturerange probably reflects continuous charging from the early Yan-shan to the late Himalayan Orogenies. The presence of bitumenindicates an earliest petroleum charging event during the late Cal-edonian Orogeny. Differential petroleum charging during theHimalayan Orogeny caused stark differences in the thermalmaturity of trapped oil and the mixing of oil with variable matu-rity, with the SHB1 fault zone receiving more intense charging oflate-stage oils than the SHB5 fault zone. The differential petro-leum charging during the Himalayan Orogeny can be explainedby preferential reactivation of northeast-trending strike-slip faults,controlled by the regional northeast 45 degrees-oriented compressive stressfield. Crude oil with high maturity would preferentiallymigrate vertically via the reactivated northeast-striking SHB1fault zone, charging into reservoirs, resulting in the current matu-rity differences in the trapped oils in the Shunbei oilfield. Theseresults illustrate the preferential vertical petroleum migrationalong the reactivated fault and the controlling role of the regionalstressfield on fault behaviors.