Multi-field Coupling Nonlinear Seepage Theory Of Multistage Fractured Horizontal Wells For Shale Gas Reservoirs

In shale gas reservoir,massive multi-stage multi-cluster hydraulic fracturing stimulation technique is the major means to improve gas production,which can form multi fractures and complex fracture network.The multi-scale flow characteristics are much more different from most conventional reservoirs.Transformed and untransformed zones of fractured horizontal wells form a multi-region structure;The stress field changed caused by the pressure decrease development,and the deformation of media caused by fracturing fluid drainaged.Thus the problem of fluid-solid coupling was outstanding and the flow pattern was unknown.So this article will directed to do some research on shale gas multi-scale nonlinear seepage rule and flow mechanism,complicated fractures flow mechanism and mathematical model,the moving characteristics of the unstable flowing pressure disturbance,Multiple media(especially the transformation zone)seepage-stress-medium fluid-solid coupling nonlinear complex seepage and the rules of the gas production of fractured horizontal Wells.Through the physical simulation experiment,theoretical analysis and numerical simulation methods,the multi-scale,multi-areas and multi-field coupling seepage simulation were realized,the research work was elaborated as follows:(1)The whole process of multi-scale flow unified model characterized by different form fracture network.This article induced the generation of the fractures by the Brazilian splitting test;observed the form of the hydraulic fractures inside the rock sample and measured the opening of the hydraulic fractures by CT scan using the X-ray;Based on the multi-scale flowing law,Aiming at the problems that the complex form of the fractures network,Explored the characterization method of different complex fracture network structure,gas flow mechanism and mathematical description methods.Then compared with conventional reservoir.(2)The three coupling nonlinear seepage flow mathematical model of bedding development shale gas reservoir was established.Because of the different flow law between the fracture network and the matrix zone,the three-zone composite model was proposed.Then the productivity equation of horizontal fractured well in consideration of diffusion,slip and desorption absorption was built.Considering the intraformational heterogeneity between layers,the bedding shale reservoir anisotropic seepage rule and factors influencing capacity was further studied;The Multi-scale flow of shale gas reservoir and the influence on the productivity were analyzed.The flow law of matrix-fractured fractures-well bore was revealed.Then he fracture spacing,the fracture opening and fracturing optimization were comprehensive scoped,and used to guide field fracture production.(3)The effective boundary dynamic prediction method was established.Using the stable state successively replace method,considering the desorption,diffusion,slippage,the permeability model of fractal distribution and Gaussian distribution was established to describe the different fracturing characteristics,the moving characteristics of the unstable flowing pressure disturbance in the matrix and fractured shale reservoir(single fracture/fractal fracture/Gaussian fracture)were analyzed;and then the rules of the gas production was analyzed.(4)The efficient development of fluid-solid coupling nonlinear seepage flow mathematical model of shale gas reservoir was established.Starting from the micro-macro dynamics seepage behavior,the fluid-solid coupling effect on the gas flow law was researched.the interactive relationship between micro and macro effective stress was figures out,the mathematical models of porosity and permeability under effective stress.Characterized by multiple zones,The fluid-solid coupling nonlinear mathematical model of the fractured horizontal well in shale reservoir was eatablished.The numerical simulation methods and techniques of fluid solid coupling nonlinear seepage was formed.Through theoretical analysis and experimental research,the typical instance well were chosed to simulation analysis and model test.The above research provided a theoretical basis for development index of shale gas productivity prediction and development index optimization.