Research On Factors Affecting Volumetric Fracturing Productivity Of Horizontal Wells In Shale Gas Reservoirs

China’s shale gas resources are abundant,but because of the shale reservoirs are low-porosity,low-permeability ultra-tight gas reservoirs,their natural productivity is quite low.And then,the gas occurrence state is different from conventional natural gas reservoirs,mostly in adsorption state and free state.And dissolved forms and others exist.Therefore,it is of great significance to accurately understand the adsorption,desorption,diffusion and seepage characteristics of shale gas migration process for the efficient development of shale gas reservoirs.Based on the full understanding of shale gas characteristics,formation mechanism,occurrence mechanism and accumulation process,this paper considering the shale gas adsorption,desorption from the multi-scale reservoir space and multi-transportation mechanism of shale gas diffusion,gas slippage and stress sensitivity,to establish a non-steady-state seepage model of dual media in shale gas reservoirs.And then,through the CMG numerical simulation software,a single well numerical simulation model of shale gas reservoir is established,and the productivity sensitive factors are analyzed.The main research results obtained are as follows:(1)Based on a large number of domestic and foreign literature investigations,systematically analyze the characteristics of shale gas generation,occurrence,migration and accumulation,and deeply understand the difference between shale gas and conventional gas reservoirs.The establishment of the steady-state seepage model lays the theoretical foundation.(2)Based on the G-K dual medium model,an unsteady seepage model considering the effects of shale gas Langmuir adsorption,Fick second diffusion law,stress sensitivity effect and gas slippage effect is established.Based on the coupling of the matrix and fracture gas seepage models,a gas differential seepage differential equation describing the horizontal wells of shale gas reservoirs is established,and then analyzed the factors affecting gas well productivity.(3)At present,numerical simulation,analytical method,and well test data analysis are the main methods for predicting the productivity of horizontal wells in shale gas reservoirs.Based on the productivity model of the fractured horizontal well in the Genliang Guo reservoir,a modified model is proposed.In addition,the gas seepage in the shale gas reservoir is divided into the flow at both ends of the fractured fracture and the fracture,and a page based on a single crack is established.Steady-state productivity evaluation model for rock gas reservoirs.(4)Based on the CMG numerical simulation software,I established a single well numerical simulation model of shale gas reservoir fracturing horizontal well,and then,researched the reservoir and engineering parameters affecting of gas well productivity.The results shows that with the increase of matrix/fracture permeability and Langmuir pressure,the decrease of bottom hole pressure,and the increase of horizontal wellbore length and artificial crack half-length,the gas productivity shows an increasingly trend,in the other word,those parameters are quite sensitive to well productivity.With the increase of rock compression coefficient and Langmuir volume,the gas well productivity changing is not obvious,that is,the rock compression coefficient and Langmuir volume are less sensitive to gas well productivity;as the artificial crack spacing increases,the gas well productivity is generally continuous.The upward trend,but not the smaller the crack spacing,the higher the capacity.