HYDROCARBON ACCUMULATION MODEL FOR THE 1^ST MEMBER OF SHUANGYANG FORMATION IN MOLIQING RIFT, YITONG BASIN

The Moliqing fault-depression is a sub-tectonic unit located in the southernmost of the Yitong Basin, which has experienced four stages of tectonic evolution since Paleogene, i.e. transtension, thermal subsidence, transpression and squeezing. In this paper, we described the characteristics and distribution pattern for the 1st member of Shuangyang Formation in the Moliqing rift, upon which the sources of high pour point crudes and gas, the migration paths and the formation of hydrocarbon accumulation are studied in order to build up the accumulation models for more successful exploration. The high condensate oil mainly occurs on the east and west slopes of the sag. The origin of high pour point crudes are related to organic matter types of the source rock and environment. The distribution depends upon the low maturity of organic matter and the migration. Gas is mainly distributed in the southeastern region where the organic matters are in low maturity. The oil and gas accumulated in the 1st member of Shuangyang Formation mainly come from the Shuangyang Formation. The fan delta and sublacustrine fan on the slope of the sag, faults and unconformities are the main channels for lateral migration. It is hard for the oil and gas to migrate to the distant end of the sag due to shortage of migration force and/or the disconnection of transport system. Therefore, the distribution of source rock, sand bodies, faults and unconformities are the main controlling factors of hydrocarbon accumulation. In the Yi6 area, however, the basement suffered from later tension, faults and low permeability reservoirs may provide channels for low matured gas to move to higher areas.