Study On Natural Gas Accumulation In Shilijiahan Area Of Ordos Basin

In recent years,Chinese natural gas is highly dependent on foreign countries.The State Council has proposed accelerating the scale of oil and gas resources development to promote the growth of domestic oil and gas reserves and production.As a favorable exploration area of the Upper Paleozoic natural gas in Ordos Basin,it is very beneficial to study the geological conditions and characteristics of gas accumulation in Shilijiahan area systematically,and precisely determine the time and period of gas accumulation.Through the analysis and processing of the existing data,the geological conditions and characteristics of the accumulation in the study area are studied.The study shows that the source-reservoir-cap conditions of Shilijiahan area are perfect,and the source rocks have reached the condition of large amount of hydrocarbon generation.The lithological traps are mainly developed in the area,and there are a few tectonic-lithological traps.The traps were formed earlier than the peak of hydrocarbon generation.The upper Paleozoic strata are well sealed,which is conducive to gas accumulation and preservation.The natural gas in the study area is of organic origin and is generally characterized by wet gases.The gas test results show that member 1 of Xiashihezi Formation has the best gas content,and the gas layer is mainly distributed in the southwest of the study area,while the water layer and dry layer are mainly in the northeast.By measuring vitrinite reflectance of samples from Shanxi and Taiyuan Formation in Wells Jin 6,Jin 7,Jin 53,the restoration of the fourth erosion thickness and the correction of burial history are completed.The fourth erosion thickness of the three Wells was 720 m,900m and 730 m,respectively.Through the fluid inclusion experiment,the temperature measurement data were obtained and combined with the corrected burial history map,it was concluded that there were two stages of gas accumulation in the study area.The first stage was a small range of gas accumulation in the study area,which occurred in the Late Jurassic to Early Cretaceous(168Ma～139Ma).The second stage was the main accumulation period in Shilijiahan area,which occurred in the late Early Cretaceous(133Ma～106Ma).