Hongshan Strike-Slip Inversion Structures and Petroleum Exploration of Qaidam Basin

Hongshan belt located in central part of Northern Qaidam basin, approximately western segment of Zongwulong mountain of Southern Qilian is composed of Mesozoic and Cenozoic and bounded by two major reversed faults respectively at its north and south sides is. Double layers of structures developed over the belt by compressively oblique slip of Qilian Mountains with Northern faults of Qaidam block during later Hymalaya stage. Faulted anticlines developed during later Yanshan orogeny distribute beneath Hongshan belt and structural traps are of faulted anticlines and blocks. For the primitive depression of Mesozoic, the principle distribution direction was NEE controlled by buried faults with NEE and NNW trends. Tectonic evolution, sedimentation and geochemistry study show that Hongshan depression exhibited relatively rapid subsidence and much effective oil accumulation. Argillite and oil shale are the source rocks; reservoir formations are distributed within Jurassic, Cretaceous and Tertiary. Upper Jurassic and thick Neogene red mud are regional cap rocks. Even though active light oil seeps occur along the NE trends fractures over Hongshan mountains implying that oil pools at depth might be the leakage sources, success haven’t been met after several exploration wells had been drilled. The study shows that faulted anticlines with unconformities beneath thrust faults underwent minor deformation during later Yanshan and later Hymalaya orogenies are favorable for hydrocarbon accumulations. These traps which formed prior to source rocks maturation are favorable for hydrocarbon accumulation.