Research On Multiple Migration Mechanisms And Well Testing Theory For Fractured Wells In Coal Seam Gas Reservoirs

As a kind of self-sourcing and self-preserving unconventional natural gas resource,Coalbed methane(CBM)are usually stored in natural fractures and adsorbed on the surfaces of matrix particles.China is rich in CBM resources and it's important for relaxing energy crisis,reducing natural gas external dependence and building environment-friendly society to develop CBM more efficiently.Since coal seam have complex pore structures,multi-scale pores,and special gas storage phenomenon,the transportation of CBM in reservoirs are usually driven by multiple flow mechanisms,such as desorption from the surface of matrix particles,diffusion in coal seam matrix and Darcy flow in natural fractures and hydraulic fractures.As a result,the research methods for conventional natural gas are not applicable to CBM.Based on Natural Gas Engineering,Fluid Flow in Porous Media,Mathematical Physics Equation,Well Test Analysis,and Computer Programming,the dissertation established mathematical models of CBM for multi-wing hydraulic fractured wells(MFVW)with consideration of adsorption-desorption,diffusion,and laminar flow,then the bottom hole transient pressure responses of MFVW were analyzed,which can provide theory basis for CBM dynamic development.The major research conclusions are as follows:(1)Based on many domestic and foreign literatures,the dissertation analyzed reservoir characteristics of coal seam and summarized the multiple transport mechanisms,then the continuous line-source solution for coal seam gas reservoir was modeled,by coupling adsorption-desorption,diffusion,and laminar flow.(2)On the basis of continuous line-source solution,the dissertation provided the well test mathematical model for MFVW,plotted the type curves,and identified different flow regimes.The effects of adsorption-desorption constant,inter-porosity coefficient,storativity ratio etc.on type curves were analyzed,then the comparison between MFVW and two-wing fractured vertical wells were made.(3)The dissertation provided the well test mathematical model for MFVW with consideration of finite-conductivity hydraulic fractures,plotted the type curves,and identified different flow regimes.The effects of the conductivity of hydraulic fractures,the number of hydraulic fractures,and the angles of hydraulic fractures etc.on type curves were analyzed,then the comparison between MFVW and two-wing fractured vertical wells were made.(4)The dissertation provided the well test mathematical model for MFVW with consideration of stimulated reservoir volume,plotted the type curves,and identified different flow regimes.The effects of adsorption-desorption constant,inter-porosity coefficient,storativity ratio etc.on type curves were analyzed,then the comparison between MFVW and two-wing fractured vertical wells were made.(5)The dissertation provided the well test mathematical model for MFVW with consideration of stimulated reservoir volume and finite-conductivity hydraulic fractures,plotted the type curves,and identified different flow regimes.The effects of conductivity of hydraulic fractures,the number of hydraulic fractures,and the angles of hydraulic fractures etc.on type curves were analyzed,then the comparison between MFVW and two-wing fractured vertical wells were made.(6)The dissertation provided the well test mathematical model for MFVW with consideration of gas-water flow through porous media,plotted the type curves,and identified different flow regimes.The effects of water saturation,adsorption-desorption constant,inter-porosity coefficient etc.on type curves were analyzed.(7)The results of models provided in this paper were compared by the results obtained by commercial software,the agreement between the two models of transient pressure responses is excellent,embodying the superiority of our models.