Research On Production Simulation Based On Multiscale Flow In Shale Gas Reservoir With Stimulated Reservoir Volume

At present,shale gas in China has been switched to the development stage iii the demonstration area.However,influenced by the domestic shale gas development policy of making research and perfonning practice at the same time,the associated studies of basic theory always can not keep up with the field engineering practice,leading to the lack of enough scientific basis for shale gas development,especially,prediction of the stimulated reservoir volume(SRV)in shale gas reservoir and understanding the complex flow mechanisms and control factors in multi-scale space including kerogen,inorganic matrix and hydraulic fracture.Prediction of the stimulated reservoir volume and evaluation of-the production performance are the key problems that needs to be solved as for effective development of shale gas reservoir.Therefore,this dissertation made a detailed study of the above problems,explored the generation mechanism of tensile and shear failure areas in hydraulic fracturing of shale gas reservoir,and analyzed the complex gas flow behavior in multi-scale shale.Finally,the new models incorporating stimulated rock volume forecast and production performance simulation are proposed,and the main contents include the follows:(1)Based on the theory of fluid mechanics and rock lnechanics,considering that the shale reservoir is composed of a large number of natural fractures and using continuum approach,combining with tensile or shear failure criterion of natural fracture,we developed a coupled flow fluid and geo-mechanical model to predict the SRV during the process of main crack propagation.The tensile and shear failure regions are modelled using numerical simulation method,and the mathematical model is matched and calibrated with the field micro-seismic data.Finally,a sensitivity study was perfonned to analyze the effects of reservoir parameters and treatment parameters on the SRV shape,shear stimulation volume,tensile stimulation volume and the SRV permeability.(2)On the basis of the Knudsen number criteria,considering different flow behaviors in nanometer pore,including viscous flow,slip flow,transition flow,free molecular flow and surface diffusion of adsorbed gas,the effect of adsorption layer and stress sensitivity on the pore radius,we established a unified matrix apparent permeability model.We studied the flow mechanisms of shale gas in nano-scale pores,and perfonned a quantitative analysis to understand the control factors of apparent permeability,and quantified the contribution of these factors on shale gas production.(3)Based on the special shale gas storage mechanism,the complex flow mechanism in different scale medium,and the natural fracture stress sensitivity characteristics,we proposed a multi-scale gas flow mathematical model with consideration of the coupling flow and solid deformation effect.The model is a three porosity/two permeability model considering the following gas release sequence:shale kerogcn-inorganic matrix-fracture.In this model,the complex flow behaviors,incorporating slip flow,Knudsen diffusion and surface diffusion,are characterized through the definition of apparent permeability,and achieved the coupling and transformation of shale gas flow from the microcosnic to macrocosmic.(4)By using the finite difterence method,the solid defoniation equation and seepage differential equations,including the shale kerogen,inorganic matter and tracture system are discretized,the corresponding numerical model are obtained.A method is given to solve the coupling equation of gas seepage and solid deformation fields.(5)The production model is matched and verified based on the field production data,and the effects of effective stress on the fracture penneability and production performance are explored.The impacts of hydraulic fracture parameters,including the size of SRV,the ratio of SRV width and length,the penneability of SRV and main fracture conductivity on production are studied to get the optimal fracture parameters.In addition,we analyzed the influence of perforation cluster number and cluster spacing on gas production with consideration of multi-cluster fracture stress interference.We also explored the influence of reservoir parameters related to shale kerogen,inorganic matrix and natural fracture on gas production.Finally,the workflow integration of SRV simulation to production prediction was actualized by doing a parametric study to investigate the relation between production and treatment parameters(injection fluid volume,pumping rate and fracturing fluid viscosity),as well as reservoir properties(horizontal principal stress difference,natural fracture azimuth angle and fracture stiffiness).