Characteristics Of Natural Gas Accumulation In The Upper Paleozoic In Daniudi Gas Field

With the feature of simple structure, tight reservoir, abnormal low pressure, several gas bearing intervals in the upper Paleozoic in Daniudi gasfield, using the comprehensive material of geology, well logging, drillinglog, testing, the transporting system, migration agent, tracer of migration and accumulation are focused on studying. And then establish the model of gas accumulation, and discuss the factors of gas accumulation.Study the condition of source rock, reservoir, cap, and research the types of transporting system through studying the distribution of sandstone combining with the distribution of fracture which was previous study. The result shows the gas migration and accumulation mainly through sand and sand-fracture transporting system. Through researching the compaction feature of mudstone, the pressure was calculated. It is discovered though the research that the difference of the pressure between resource rock and reservoir was the main migration agent. The results of gas component and carbon and hydrogen isotope show that coal gas migrated vertically and formed the gas accumulation. The maturity of resource rock in southwest is stronger than the one in northeast. Using the homogenization temperature of inclusions. combining with the thermal evolution history, the accumulation time could be divided two parts:90~120℃and 120～150℃, corresponding to Late Triassic -Middle Jurassic and middle Jurassic- late early Cretaceous respectively. And the late early Cretaceous was the key accumulation time. According to the factor of resource rock, production layer and cap, there are two accumulation combinations: inside source type and near source type. Inside source type corresponds to Taiyuan and Shanxi group while source type corresponding to Xiashihezi group.Basing on analyzing the resource rock, reservoir, caprock, transporting system, migration agent and tracer of migration and accumulation,it is pointed that the gas accumulation of Deniudi gas field in the upper Paleozoic was the result of coal gas accumulation through vertically migration under the differencepressure between resource and reservoir layers in the pressure compartment. The main factors of affecting gas accumulation are the gas generation intensity, the quality of reservoir,the internal composition of pressure compartment, transpoting system and migration agent.