Controls on the Enrichment of Oil Pools in Qingxi Sag,Jiuxi Basin
YANG Zhi ming 1 WANG Qi 2 SHI Ji an 2 LI Man ru 1 WANG Lei 2 1( Research Institute of Yumen Branch,CNPC,Yumen Gansu 735200 ) 2(State Key Laboratory of Gas Geochemistry, Lanzhou Institute of Geology,CAS, Lanzhou 730000)
A series of Cretaceous lacustrine mudstone, shale, dolomitic mudstone and argillaceous dolostone comprises the main source rocks of Qingxi Sag in the study area. During deposition, the Qingxi Sag was a closed to semi closed rift basin with strong reducing conditions that was favorable for the preservation and transformation of organic matter. In addition, the thickness of the source rock is very great with the ratio of source rock to strata over 50%, together with mixing organic types, high content of organic carbon (1%), which all provided the important material basis for oil pool formation. Himalayan tectonic movement formed lots of compressional reverse faults, shears faults and structural fissures, and resulted in strata and structure overstacking to provide impetus and space for organic matter maturity, migration and accumulation of petroleum.