Study On Stratigraphic Characteristics Pressure And Controlled Gas Function Of East Slope Of Shaximiao Group In The Western Depression Of The Sichuan Basin

The eastern slope in western Sichuan depression is located in the central area of the western Sichuan Basin;its area is 2400 square kilometer.Western Sichuan depression is a foreland basin which is trusted by Longmen Mountain since indo-Chinese epoch.Shaximiao formation of Middle Jurassic is one of the major oil and gas bearing systems.It divided into three oil group,namely JS1,JS2,and JS3.In the geological history,from the early Jurassic to early Himalaya,the strata pressure of western Sichuan depression is an abnormal high pressure.From shallow to deep,the strata pressure of Shaximiao formation showed an increasing trend.Thus,the strata pressure of research area is overpressure.There are rich oil and gas resources in the research area,but the study area with complicated reservoir-forming rule results in overpressure brings a lot of negative factors to exploration works.Thus,by summarizing the basis of previous studies,we analyze the formation mechanism of overpressure and recover the chart of key position's strata pressure.Then we analyze the overpressure's control action on the later reformation of natural gas reservoir.Thus,making a comprehensive and systematic understanding to the abnormal high pressure and its control of oil and gas reservoirs in the Shaximiao formation from the western Sichuan depression has a positive effect on oil and gas exploration in the next phase of the work area.Under the guidance of petroleum geology,the system of oil and gas combine the geological theory of sedimentary petrology,logging geology and geology of natural gas develop geologic models and through the comprehensive analysis outcomes of testing and well logs data.Based on the analysis of the results of previous studies,this paper studies the characteristics and distribution of abnormal formation pressure.Firstly,by analyzing the measured pressure data: with the deepening of the stratums depth the formation pressure increases in study area,there is no significant variation in longitudinal;Then,through consulting massive literature,the main reason for the formation of abnormal high pressure in the study area is the Himalayan movement caused the uplift and erosion of strata,tight reservoir with low porosity and low permeability leading to oil and gas can not be exhausted timely and the ancient hydrostatic pressure remains preserved.With the strata uplift and denudation,formation pressure becomes higher;Secondly: select the appropriate calculation method to predict the formation pressure in 8 important stratums of study area,and then draw the fluid potential map;Thirdly: combine with previous research to study on the controlling effect of abnormal pressure on the later transformation of natural gas reservoir and themigration path of oil and gas.In the study of the late adjustment of the formation gas reservoirs,it is necessary to establish a geological model based on the gas supply model,the transport grid model and the transport dynamic model.We use the Arcgis software to simulate the migration route of hydrocarbon accumulation in the late stage.During the process of fluid migration simulation,the ancient gas reservoir formed at the end of Yanshan is used as the model of gas supply,and the sandstone dredger with good connectivity is used as the transport grid model.Because of the study area belonging to abnormal high pressure system and oil and gas migrating mainly under this high pressure,we regard the abnormal high pressure as migration dynamic model.Finally,we map the later migration path of the gas reservoir to be superimposed on the actual distribution of oil and gas in the work area to test the rationality of the simulation forecast.The result shows that compared with the oil and gas migration path simulated by the water potential as the driving force,the prediction result of the oil and gas migration path simulated by the momentum as the transportation power has a better correspondence with the actual distribution of oil and gas.Based on the analysis the relation between the adjustment and reconstruction of gas reservoir and simulation of oil and gas path and oil and gas distribution in study area,we found that the tectonic uplift and denudation in the Himalayan mountain are the keys to the adjustment of the paleo gas pools in the late Yanshan period.The source of oil and gas is the ancient gas reservoir formed at the end of Yanshan,and the migration path is the sand body to clear the frame,and the fluid potential is used for the migration.Therefore,the superiority migration path of oil and gas is controlled by the sand body grooming framework,the abnormal high pressure and the structure.Finally,the abnormal high pressure formation in the study area mainly gathered in Hexinchang structural belt and Zhongjiang-Huilong structural belt,the oil and gas accumulated in the high point of the structure formed tectonic-based lit-ho logic gas reservoirs.