Accumulation Mechanism And Regularity Of Gas Distribution Of Tight Sandstone Gas Reservoir In The Upper Paleozoic Of Eastern Ordos Basin

There are several tight sandstone gas reservoirs whose accumulation mechanisms arecomplicated in the Upper Paleozoic of Eastern Ordos Basin. Based on the previous researchresults, including the abundant materials of loggings, core observations, laboratory analyses,gas testing, comprehensively using the latest academic theory of the petroleum and natural gasgeology, reservoir geology, geochemistry, fluid history analysis, and reservoir-formingdynamics, etc., this article combined comprehensive geological analysis with advancedexperimental analysis technology current characteristics with historical analyses, staticanalyses with dynamic studies, as are the basic research methods. From the basis of gasreservoir geological characteristics, analyzing the natural gas migration and accumulationcharacteristics and reservoir-forming pattern, main control factors of the gas reservoirformation and distribution are comprehensively analyzed，and ifnally wc reached the followingmain understanding:(1)Source rocks in the Upper Paleozoic of Eastern Ordos Basin produce abnormal highpressure in the process of hydrocarbon generation，And they provides the main force for gasprimary migration, also urges source rocks to generate (micro) cracks which can serve aschannels for the gas primary migration. Two expulsion mechanisms including crackingexpulsion and diffusion expulsion are formed, and the vertical migration and near-distancemigration are main mode of gas migration in Eastern Ordos Basin.(2)The gas filling time is divided into2phases in the Upper Paleozoic of Eastern OrdosBasin，whose first phase was similar in time to the reservoir densiflcation, as is considered as"Reservoir tightening consistent with its forming timèŠ'-The Second phase of main reservoirsforming is later than reservoir densiflcation, which is considered a^^Rcservoir forming laterthan its densificatiori’.(3)Regularity of gas distirbution of natural gas in the Eastern Ordos Basin: The relativelyhigh hydrocarbon generation intensity is the prerequisite and mateiral foundation of gasreservoirs, controlling gas distribution regionally; in cach gas field and different gas layers,the strong heterogeneity and high quality reservoirs which have better properties and (micro) carcks，provide conditions for gas filling; and the favorable sealing capacity of the layer is theadvantage for gas preservation conditions in the Upper Paleozoic.