The reservoir forming conditions and exploration risks of middle-deep strata in Ledong area of the central Diapir zone, Yinggehai Basin

The prospecting of mid-deep layers of Ledong area in the Yinggehai Basin is at the exploration stage at present. Based on regional geology, seismic data, boreholes as well as geochemical data, the conditions of natural gas accumulation and its controlling factors of the middle-deep layers in Ledong area were analyzed, including the characteristics of source rocks, the styles of reservoirs and traps, petroleum conduction system and accumulation risks. According to the geochemical features of the natural gas in the shallow layers, they belong to mature-high mature coal-derived gas, which is sourced from the mature-high mature humic source rocks in the Miocene Meishan-Huangliu Formations. Moreover, the drilling of well L22-1-7 confirmed the existence of this set of source rocks and it indicated that Ledong area has a good condition of source rocks. Although individual borehole revealed that the development and the reservoir physical properties of the middle-deep layers in Ledong area were not promising, we can't ignore the whole area. The seismic and geologic data showed that the styles of reservoirs of the middle-deep layers in Ledong area are dominated by low stand sandstones, including coastal sand dams, slope fans, floor fans and channel sandstones, etc., which were formed in the forced regression environment and should have good physical properties. What's more, vertical faults and microcracks system resulted from upwarping and piercing forces of diapirs in Ledong area provided high efficient conduction pathways for vertical migration and accumulation of deep hydrocarbons. Though there are many exploration risks and some uncertain factors in the hydrocarbon accumulation of middle-deep layers in Ledong area, especially the key controlling factor on the distribution and physical properties of reservoirs, and nonhydrocarbon gas risks, the middle-deep layer gas accumulation conditions and exploration prospects are unassailable. ©, 2015, Science Press. All right reserved.