Research On Seepage Characteristics Of Shale Under The Coupling Of Seepage And Stress

As a new type of energy,shale gas is changing the global energy structure.China's shale gas reserves are abundant,Guizhou Province shale gas recoverable resources ranks third in the country.Hydraulic fracturing technology is mainly used in shale gas production.Therefore,the study on the infiltration characteristics and damage mechanism of shale under seepage-stress coupling has important theoretical significance and engineering value.Based on the research methods of physical experiment and numerical simulation,the geological background,regional tectonic evolution,infiltration mechanism,damage mechanism,meso-structure evolution and destruction and instability behavior of the Lower Cambrian Niutitang shale in Fenggang area,Guizhou province were studied.The research results are follows:?1?Based on the field geological survey,the north-south,NE and NNE faults and fold structures were developed in the study area.The burial depth of shale in North Guizhou is deeper and the development is difficult.?2?Based on the Nuclear Magnetic Resonance Test,the pore size distribution of shales is dominated by nanopores,with a few micropores,which mainly developed intergranular micropores and interlayer micropores of clay minerals.Based on the X-ray diffraction experiment,the Niutitang shale minerals are mainly brittle minerals and clay minerals.The brittle minerals mainly include quartz,calcite and carbonate minerals.The clay minerals mainly include smectite,illite mixed layer.?3?Based on the rock servo triaxial test,the relationship between confining pressure,osmotic pressure and permeability was obtained,and the relationship between permeability and different stages of deformation was analyzed.The relationship between local compression zone and permeability was studied,and the relationship between the damage evolution and permeability in different stages of shale deformation was discussed.The correlation between permeability and pore fracture in the local compression zone formed by shale destruction was mainly analyzed.The presence of compression zone has the effect of inhibiting permeability.The compression zone is the reason why shale permeability evolution behind the damage and evolution process of shale.?4?Based on the finite element numerical simulation software RFPA^2D-Flow,the evolution,destruction and instability of the mesostructures under the seepage-stress coupling were analyzed.The comparison of the destruction process of the different osmotic pressure,the initiation stress and the peak intensity were analyzed.It is found that tensile stress and osmotic pressure are the factors leading to unstable crack growth.The stress span interval of shale is negatively related to the seepage pressure,which indicates that the shale begins to soften under the influence of osmotic pressure.Osmotic pressure is one of the main factors that affect the strength and damage evolution of shale.