Study Of Fault Sealing By Geochemical Characteristics In Jiaoshiba And The Preservation Of Shale Gas

The fault is the main controlling factor for the preservation of shale gas in the Fuling shale gas producing area so it is important to evaluate the vertical sealing of faults to evaluate the favorable area of shale gas preservation.In order to evaluate the vertical sealing property of fault accurately and to evaluate the favorable area of shale gas preservation,a method for evaluating the vertical seal of faults in carbonate strata is established.Through the trace of the strontium,carbon and oxygen isotope data of the calcite vein,which is induced by the fault,we can judge the time and the possibility of opening of different parts of the fault.Strontium isotope is an effective tracer index because it is not easy to be fractionated and can be compared with the age.The carbon and oxygen isotopes have a strong response to the formation of calcite veins,such as fluid temperature,fluid type,and the influence of oil and gas.According to fluid tracer map we can know the source rock of the fluid formed the calcite vein in the stratum which means that the stratum and the fluid source stratum of the filling and filling vein have been connected by fault in the geological history.The more times the fault is opened,the larger the connectivity,the worse the vertical seal of fault.This method can be used to evaluate the difference of seal in different parts of the fault.The research process includes sample collection,sample screening,analysis and test,fluid tracer mapping,vertical sealing evaluation of fault,and prediction of favorable area of shale gas storage.We use this method to evaluate vertical seal of faults around the anticlinal belt Jiaoshiba.On this basis,the influence of vertical seal of fault on the preservation condition of shale gas in Jiaoshiba is studied.The evaluation results show that the strata under the Silurian strata is communication in this area and there is a period of strontium rich fluid from deep crust.But protected by decollement from mudstone in the Silurian strata,the period of strontium rich fluid can't migration to upper strata through faults.This area at last experienced two times of tectonic movement in the late period.Controlled by the Silurian mudstone and jialingjiang formation gypsum rock,different faults have obvious differences.The vertical sealing of faults in the middle of the south of Daershan fault zone,Fangdoushan fault zone,the south of Wujiang fault zone are bad.The vertical sealing of faults in the north of Wujinag fault zone,the south of Tiantaichang fault zone are medium.The vertical sealing of faults in the north of Fangdoushan fault zone,the south of Fangdoushan fault zone,the north of Tiantaichang fault zone are good.In the area with poor vertical sealing,there is a phenomenon of well leakage and low productivity of gas wells,which indicates that the poorer the vertical sealing property of the fault,the worse the shale gas preservation conditions.The method can effectively guide the exploration target optimization.