The Micro-nano Pore Structure And Gas Storage Capacity Of The Shale

The shale gas revolution in America led to a worldwide shale gas research boom.Pilot experiment begun to take effect in many early geological evaluation and exploration development.Shale gas resources in China are huge and widely distributed.But shale gas blocks are basically located in the complex tectonic area besides oil and gas basins,whose deformation is strong and geological conditions are complicated.It restricts China's shale gas accumulation,occurrence and development methods.Therefore,it is of great significance to study the effect of tectonic deformation on the micro-nano pore structure and gas storage capacity of the shale,which will help China's shale gas to achieve commercial exploitation.This study firstly analyzes the degree and characteristics of shale tectonic deformation from macro and micro scale.Shale samples with different degrees deformation carried out total organic carbon content(TOC),rock pyrolysis,asphalt reflectivity(Ro),X-ray diffraction,scanning electron microscopy(SEM),low-temperature nitrogen adsorption(LTNA),mercury intrusion porosimetry(MIP),nuclear magnetic resonance(NMR),methane isothermal adsorption experiment.By comparing experiments,their results are used to analyze the effects of organic matter(organic carbon content,organic matter type,organic matter maturity),clay mineral and tectonic deformation on the micro-nanometer pore structure characteristics of shale.Then methane isothermal adsorption curve is obtained by adopting isothermal adsorption simulation and Langmuir model fitting.The ideal gas state equation is combined with the Mariotte's Law to calculate the free gas content.Thus,we can compare the impact of geological factors on the shale gas storage capacity.The above research methods are applied to the shale of Lower Cambrian Lujiaping Formation in Xiuqi Township and Longtian County,northeast of Sichuan Basin.The results show that organic matter pore is the important structure of the shale reservoir space,and is proportional to the micro-nano pore development degree.Organic matter content is the core factor affecting the shale gas content,while compared with it,the impact of clay,humidity on the shale gas content is relatively small.With the enhancement of tectonic deformation,in the macro,multiple fissures disappear gradually,and grow obvious folds,crumpled phenomenon.In the micro,micro-nano pores and specific surface area increase gradually,as the same to adsorption site.So the adsorption capacity increases.But the porosity reduces.On the whole,shale gas content is positively correlated with the reservoir pressure.When the reservoir pressure is low,adsorption gas is as the main.When the pressure is large enough,the adsorption gas reaches saturation point,and free gas content continues to increase,occupying a greater advantage.Within a certain TOC,the contribution of tectonic deformation to the shale adsorption gas content can compensate for the deficiency of TOC,increase the shale adsorption capacity,but have a negative effect on the free gas reservoir,by comparing the shale gas content of different organic matter content and tectonic deformation.