Numerical Calculation And Application Of Low-permeability Gas Reservoirs 3D Situ Stress Field

There are huge amounts of low-porosity and low-permeability reservoirs in our country,which will be exploited principally in the future.Owing to the low osmotic pressure,higher flow resistance and low transpiration,it is difficult to increase the recovery and injection ratio,leading to higher development costs.It is essential to improve development effectiveness by transforming low-permeability oil and gas field.Hydraulic fracturing is required generally when the low-porosity and lowpermeability reservoirs are developed.Fracturing generally will bring poor affection or even failure,due to poor reservoir permeability,complex pore structure and inhomogeneous geology.The high-accuracy simulation results of situ stress field are widely used in the development program optimization and fracturing design.The paper reviews the numerical simulation situation for hydraulic fracturing and situ stress field,and points out the achievement and shortcomings,then proposes the basic research methods.The basic concepts and theory of rock fracture mechanics,damage mechanics and XFEM are introduced briefly.Basing on core consolidated triaxial compression test and logging data,rock mechanics parameters 3D model is established.Using VB.NET,the software "logging data analysis and application" is Developed,by which the 3D rock mechanics parameters is calculated and spatially distributed.According to the PETREL geological model,high-precision 3D finite element model is established combining with software Image Ware.Loads and boundary conditions are built using fast search technology.3D situ stress field distribution regulation is analyzed combining with geological features.The Paper analyses fracture geometry,equilibrium equation of saturated porous media and continuity equation of fluid.Then,a single fracture dynamic expansion mathematical model is established by introducing crack initiation and propagation criterion.According to situ stress field and fracturing data,a single fracture axisymmetric extended finite element model is built by ABAQUS,and 3D dynamic crack propagation process is simulated.The variable regulations of some parameters are analyzed such as maximum principal stress,minimum principal stress,pore pressure and fluid loss.On the basis of the above,the effect of stress field,void ratio,permeability and injection on width and length of fracture is studied,using the “single-variable method”.