致密砂岩气藏变启动压力梯度实验及表征模型研究OA

Tight sandstone gas reservoirs have the typical characteristics of low porosity,low permeability and complex pore throat structure,and exhibit obvious nonlinear flow patterns in the middle and late development stages.The threshold pressure gradient(TPG),as a key parameter of nonlinear flow in tight sandstone gas reservoirs,is of important theoretical significance and engineering value for the productivity evaluation and development plan optimization of gas reservoirs,but its dynamic evolution patterns and controlling factors are lack of systematic research.Taking a certain block in the Sulige Gas Field as an example,this paper selects typical core samples to conduct TPG experiments under varying pore pressures,simulating its evolution patterns during the depletion development of gas reservoirs.In addition,a mathematical characterization model of variable TPG incorporating pore-throat structure,capillary pressure and boundary layer effect is established on the basis of fractal theory,Hertz contact theory,and boundary layer theory.The following results are obtained.First,water saturation and interfacial tension are directly proportional to TPG,while porosity,Young's modulus and wetting angle are inversely proportional to TPG.Second,porosity and water saturation have greater impact on TPG.In comparison with the initial stage of development,these factors exert a more substantial influence during the middle and late stages.Third,a variable threshold pressure gradient effect is present within the gas reservoir.TPG is smaller in the initial stage of development than in the middle and late stages,and its variation range is larger in the middle and late stages.In conclusion,the variable threshold pressure gradient and productivity model established in this paper can accurately characterize flow characteristics,and lay a methodological foundation for improving the prediction accuracy of gas reservoir productivity.