| In order to study the comprehensive sealing ability of the cover layer of Sulige Gas field in Ordos Basin and its control effect on natural gas accumulation,combined with the geological data of drilling,seismic,logging and gas testing in the study area,through the method of combining macro and micro,geological anatomy and experimental analysis,The sealing characteristics of two sets of mudstone cap rocks,upper Shihezi Formation and Lower Shihezi Formation,which are closely related to the accumulation of Sulige gas field,are studied in detail,and their comprehensive sealing ability in each geological period is quantitatively evaluated.The results show that:1.The regional cover of upper Shihezi Formation of Middle Permian and direct cover of Lower Shihezi Formation of Middle Permian in Sulige area have macro development characteristics of large thickness,good continuity and high mud-soil ratio.2.Based on the fitting formula between logging data and measured displacement pressure of mudstone,and in combination with burial history data,the micro-sealing ability and evolution prediction technology of cap rock are established,so that the upper and Lower Shihezi formation mudstone cap rock have strong micro-sealing ability in different geological periods,reaching more than 5MPa.3.Sulige gas field is currently a negative pressure system as a whole,and the pressure coefficient increases gradually from south to north.The gas field is characterized by atmospheric pressure system at the end of Jurassic by pressure recovery technology.The variation of gas field energy has a great influence on the preservation conditions of natural gas.4.Based on the preservation mechanism of cap rock,three parameters including cap rock thickness,cap rock displacement pressure and gas reservoir energy are selected to establish the evaluation formula of cap rock comprehensive sealing ability,and the evaluation criteria are determined based on the characteristics of large and medium-sized gas fields in China.Three evaluation parameters according to the research of the prediction data of different geological period,the main cap rock comprehensive sealing capacity of each geological period is evaluated,and get the stone box set and under the stone box set of mudstone caprock in nowadays and the late Jurassic sedimentary whole belongs to stronger closed ranks,with the formation of large and medium gas sealing conditions,Only at the end of Jurassic in the western part of the weak sealing capacity of the region.5.The two sets of mudstone cap rocks have large macroscopic thickness and are widely distributed in the study area.In addition,faults are not developed in Sulige area,so the damage to cap rocks can be ignored and oil and gas can be effectively sealed in space.Two sets of caprock sealing capacity to form effective period before the period of hydrocarbon source rocks of hydrocarbon generation,so for closed to enter the region layer is effective in time of natural gas,is only the cover sealing capacity and gas enrichment degree of dynamic evolution do not match,making comprehensive gas natural gas in a closed ability is insufficient,the gas reservoir pressure system is mainly for the negative pressure system. |
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