Research On Tectonic Characteristics And Controlling Gas Of Majiagou Formation In Su 203 Well Area, Ordos Basin

This article is based on the theories of plate tectonics,by integrating the method of oil and gas basin integrally,dynamically and comprehensively.Upon the comprehensive analysis of the predecessors' research results,then analyze more than 600 exploratory well data in the study area,studying the characteristics and tectonic evolution about Ordovician MaJiagou group.From analyzing the angle of structural evolution,and the distribution and evolution of hydrocarbon source rock,distribution and evolution of the reservoir,the types and forms of the trap,and hydrocarbon migration path and mode,etc.And we summarize the controlling effects of gas accumulation which controlled by structural evolution.Some conclusions are listed as follows:Before the Carboniferous period,the structural feature of Ordos basin shows a trend that high in the West and lower in the East.The middle reservoir-source rock combination of Majiagou formation was missing near the central paleouplift.The strata gradually thickener from west to east in east of central paleouplift.Tectonic framework in central basin showed for lung and concave.This kind of structure pattern has lasted until the end of the Permian.During the Triassic period,influenced by indosinian movement,north east trending of lung and concave has been completely disappeared in the basin.The three sides of west,north and east in our study area relative to lift and forming an open to southwest of the sag basin,the deepest middle reservoir-source rock combination of the formation is in yanan.Jurassic,ordos basin has turned to mainly for east-west different points,followed by the north-south differences,so as to form the east to the west,north south face of the structure,the eastern basin is relatively steep slopes,Midwest as depression.The late Early Cretaceous basin overall performance for East West,look north to south,but this time the slopes and depressions have become more wide and gentle,recessed range becomes small,and the overall appearance of the basin is similar to now.After the end of early cretaceous late yanshanian movement,the eastern basin uplift,erosion part Cretaceous,Jurassic and Triassic strata,and gradually formed today's formation east to the west,gentle slope tectonic form.Tectonic evolution has a certain control on the formation and distribution of gas reservoir which mainly by controlling the gas source condition,the reservoir characteristics and forming trap formation and migration path.Caledonian movement makes the majiagou formation uplift and denudation,dolomite reservoir developed bedding dissolution and formed long-range solution pores which give gas accumulation a good reservoir space and migration channel.Whole Ordos basin settled in late carboniferous and accepted upper palaeozoic sedimentary,The middle reservoir-source rock combination of majiagou formation has a direct contaction with coal,upper palaeozoic hydrocarbon source rocks,forming good source-reservoir configuration relationship;hydrocarbon generation reach the peak period in early cretaceous as yanshan movement made the basin inversed,source-reservoir contact relationship changed from the a lower reservoir-type into source under the reservoir type,Nature gas accumulated in lithology changes(phase)after goes along the long distance migration path which formed by solution pores and intergranular hole.