Research On Main Control Factors Of Oil And Gas Accumulation Of Permian Changxing Formation Of Bashan Temple Structure In The Fuling Area, Eastern Sichuan

This paper summarizes the results of previous studies on various types of natural gas reservoirs in the Sichuan Basin.And combines research ideas and methods of natural gas reservoirs at domestic and abroad.Based on the exploration data,using the theories and methods such as organic geochemistry,petroleum geology,hydrocarbon accumulation dynamics,and fluid inclusion analysis to analyze gas reservoir characteristics in Bashan Temple area,especially natural gas source,characteristics of source rock,reservoir characteristics,gas reservoir preservation conditions,gas accumulation process and main control factors.I have Established a gas accumulation model and summarized the main controlling factors of natural gas accumulation.The following main results have been achieved.?1?Changxing Formation in the Bashan Temple area has a higher content of methane and CO₂ and a lower content of Heavy hydrocarbon,the natural gas in this area is the marine pyrolysis and highly mature natural gas,the carbon isotope characteristics of natural gas indicate that the gas is sapropel-type natural gas.By mean of comparison and analysis of natural gas,the source rocks in the study area mainly come from the Wujiaping Formation of the upper Upper Permian.?2?The source rocks of the Wujiaping Formation in the Bashan Temple area are thick,the maximum thickness is more than 100m.The kerogen type is type II_B,the content of TOC is higher,according to the criteria for the classification of hydrocarbon generation potential of hydrocarbon source rocks in the Paleozoic in China,the source rock in study area is mainly medium quality hydrocarbon source rock.The kerogen of source rock reached the stage of over-maturation,The source rocks have great potential of hydrocarbon generation.?3?The rock types of the Changxing Formation in the Bashan Temple area are mainly limestone and a small amount of dolomite.The main type of reservoir space is intercrystalline pores.The minerals in the pores of the reservoir show multiple filling phenomena,and there are roughly the same mineral filling sequences in different well locations,Fine crystalline dolomite/Fine crystalline calcite?Medium-crystal calcite?Medium-crystal dolomite?Coarse-crystal calcite?Gravel-crystal calcite,Bitumen is mainly formed after the medium-crystal calcite.The characteristics of carbon and oxygen isotopes and strontium isotopes in the reservoir indicate that the cave minerals in the Changxing Formation are mainly self-sourced fluids.The period of oil and gas filling can be summed up to 4 periods,Respectively corresponds to the formation period of Fine crystalline dolomite/Fine crystalline calcite,Medium-crystal calcite and Medium-crystal dolomite,Coarse-crystal,Gravel-crystal calcite.?4?There is a Triassic Formation with good capability in Eastern Sichuan,The development of overpressure is in the Lower Triassic strata in the Tushan Temple area,and the overpressure of the caprock is large,the formation of lithologic and high-pressure are plugging the Changxing Formation.According to the conditions of reservoirs,the preservation conditions of the Changxing Group in the study area were divided into three levels.Tailai 2 is Grade I storage conditions,and Tailai 201 is Grade II storage conditions,and Tailai 202 is Grade?storage conditions.Comprehensive analysis believes that the natural gas preservation conditions in the study area are very well.?5?The hydrocarbon charging time of the Changxing Formation in the Bashan Temple area is mainly Middle Jurassic,corresponding to the formation time of the Medium-crystal dolomite,Coarse-crystal,Gravel-crystal calcite.Accumulation model shows that the Tailai 2 well gas reservoir was not damaged by tectonic movement and its natural gas production was abundant;The Tailai 201 well gas reservoir suffered a structural tectonic damage and becoming a residual gas reservoir in the later period;The Tailai 202 well gas reservoir was damaged by two tectonic movements,resulting in the loss of most natural gas and becoming a residual gas reservoir.The main control factors of natural gas reservoirs in the study area are that lithologic traps are the natural gas reservoirs,high and steep tectonic fault activities determine the size of natural gas reservoirs and the overburden strata affects the storage conditions of natural gas reservoirs.