| The shale gas reserves in China are very rich,and have considerable potential for mining.In order to obtain industrial productivity,horizontal well fractionation fracturing technology needs to be implemented.After hydraulic fracturing,shale reservoir will form complex fracture networks,the fracture network mainly consists of natural fractures in artificial fractures connected with it,as the gas flow in fractures provide good channels.For understanding the characteristics and permeability of complex fracture network prediction has been the key to productivity evaluation of shale.Therefore,this paper aims at the characteristics of the formation of complex fracture network in shale reservoir after the fracturing,and the following research has been carried out:1)The shale gas storage and transport pore space is mainly comprised of nanopore and micronpore.It is concluded that the flow type of micro-nanopores in shale mainly includes continuous flow,slip flow and transition flow.According to the distribution frequency of different pore sizes,a multi-scale migration model of shale matrix is established,which can calculate apparent permeability of shale gas under different flow conditions.2)After hydraulic fracturing SRV region will form complex fracture networks in wihich consist of a large number of artificial cracks and natural cracks.In order to establish an accurate calculation model of fracture networks permeability,it is necessary to obtain a method to accurately characterize the fracture network after fracturing.In the first time,according to the fracturing fracture and the natural fracture map activated by microseismic,the fractal dimension of fracture is determined by box counting method in fractal dimension.Based on the parameters such as crack length,crack opening and location of crack distribution,two dimensional discrete fracture network is established,and the permeability of fracture network under different ground stresses is calculated.3)According to the fracture networks peremeability model and shale matrix apparent permeability model,combining material balance equation.The unsteady state productivity model of volume fractured horizontal well in shale gas reservoirs is established for the first time by continuous pseudo steady state method,and productivity prediction and influencing factors analysis of horizontal fractured horizontal well are carried out.By the in-depth study of this dissertation,the conclusions were obtained as follows:1)In the nanopore,the surface diffusion of the gas is obvious.With the increase of the pore size,the viscosity flow,the slippage effect and the Knudsen diffusion effect are enhanced.The effect of viscous flow is dominant in the large pore,and the rest is slipping,Knudsen diffusion and surface diffusion in turn.2)For the complex fracture network formed in the SRV region,the fractal dimension will increase with the increase of the fracture complexity and the density of fractures.The distribution angle of fracture has no obvious influence on the fractal dimension.The fracture density and aperture are the dominant factors to increase the permeability of the fracture networks,and provide the main channel for the gas flow.And the fracture network permeability also increases with the high fractal dimension.The fracture angle distribution has no obvious effect on the whole network permeability,but but the influence on X and Y in the direction of permeability.3)In the early stage of production,the effect of increasing the permeability of fractured network area is obvious.The output of shale gas increases obviously with the increase of fractal dimension,fracture aperture and crack length.The radius of fractured area mainly affects the initial and late production.Therefore,we can see that obtaining fracture parameters from microseismic data has a key impact on predicting shale gas output.The research results of this paper can provide theoretical guidance for productivity prediction and optimization of fracture parameters in shale fractured horizontal wells. |
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