Research On Pore Structure And Adsorption Characteristics In Shale Gas Reservoir

With the development of technology,the exploration of unconventional resources has entered a stage of rapid development.Shale gas has drawn more and more attention due to its abundant reserves.Because of characteristics of the low porosity,low permeability and adsorption in shale,it is of great significance to study the pore structure and adsorption properties of shale gas reservoirs.However,in the current research,there are some problems,such as the accuracy of pore structure is not enough,and the study of adsorption properties is not deep.In order to solve these problems,this paper mainly uses laboratory petrophysical methods to study the pore structure and adsorption properties of shale gas reservoirs,further deepen the understanding of the microstructure and adsorption properties of shale gas reservoirs.The samples studied in this paper are mainly from the Longmaxi Formation in the southeastern Sichuan Basin and Yangtze areas.Through the analysis of current research status both at home and abroad,the experiments were carried out using high pressure mercury injection,low-temperature liquid nitrogen adsorption,nuclear magnetic resonance and isothermal adsorption.The experimental principle and application of each method were also studied carefully.Through the high-pressure mercury injection and low-temperature liquid nitrogen method,the pore structure of shale was tested respectively.Based on the detection characteristics of the two methods,a full-scale shale pore structure characterization method with higher detection accuracy was established.And then,combining with the result of nuclear magnetic resonance,the conversion coefficient of T2 time and pore size distribution was calculated.At the same time,the isothermal adsorption experiment of shale was carried out before and after crushing.The adsorption gas content was used to reflect the change of pore structure of shale,and the correction model of adsorbed gas content before and after shale crushing was proposed to improve the calculation accuracy of adsorption gas content of shale in isothermal adsorption experiment.What's more,the isothermal adsorption experiment was used to study the adsorption characteristics of shale.Combined with the pore structure research results,the influence of pore structure on adsorption properties was deeply analyzed.In addition,isothermal adsorptionNMR experiments were designed to compare shale and tight carbonate rock samples with the bounds of the free gas and adsorbed gas in the T2 spectroscopy.Finally,based on the analysis of the adsorption capacity of clay single mineral,the simulation artificial sample was prepared according to the result of whole rock analysis.A multi-component calculation model of adsorbed gas content based on single mineral was proposed.