Research On The Proppant Uneven Distribution And Conductivity Of Complex Fracture Network In Shale Gas Reservoir

The key to successfulness of the multi-stage fracturing of horizontal wells is whether the pumped fracture fluid can interconnet complex fracture networks with artificial fractures,increase stimulated reservoir volume(SRV)and provide fracture network with sufficient conductivity.However,proppants and fracturing fluids are not synchronized in complex fracture network due to the low sand carrying capacity of the fracturing fluids.It directly affects the amount of proppant and distribution pattern insides of the main and secondary fractures,as well as affecting the conductivity and effectiveness of the fractures.At present,it is not clear what the distribution and layout of proppants is in the complex fracture of shale reservoirs,the improvement of fracture complexity,and the effectiveness of the network fractures.Therefore,how to deepen the understanding of proppant transport characteristics and distribution rules and master the methods to improve the effectiveness of fractures is of great significance for the efficient development of shale gas reservoirs.In this dissertation,based on the theory of solid-liquid two-phase flow,the foce and settlement rules of proppants in the fracturing fluid are studied,and the main factors controlling the sedimentation and migration of particles are evaluated.According to the characteristics of shale reservoir hydraulic fracturing and the mechanism of complex fracture diversion,a three-dimensional complex fracture network proppant transport model is established by coupling the variable-density discrete-phase model and discrete element method.The established model fully considers the interactions of particle-liquid,particle-particle,particle-wall interaction forces,thus overcomes the problem that the particle volume concentration of the general discrete-phase model is less than 10%.The flow field and concentration distribution of the proppant in fracture with different widths are analyzed,trajectory tracking of proppants in any type of complex fractures is carried out,the state of particles laid in the primary and secondary fractures is studied,and the size and morphology of effectively supported fractures in complex networks is revealed.According to the process of actual fracturing pump injection,by studying the distribution law of proppant particles with different particle sizes in complex fractures,a method to increase proppant particles preferentially entering branch fractures is proposed.The self-supporting permeability of cemented natural fractures is evaluated,and the effects of the filling mineral types,the slip degree of fractures,and the roughness of the fracture surface on the stress sensitivity of permeability are analyzed.At the same time,conducting the evaluation of different types of support,fracture channels,turning fractures,and fracture conductivity after water-rock interaction,and discussing the relationship between proppant placement status and diversion capacity under various complex fracture patterns.Aiming at different fracture morphologies,a calculation model for the conductivity of complex fracture systems is established,which takes into account the effects of proppant crushing,embedding,deformation,and time.And single fracture channels is separately analyzed,and a sensitivity analysis of conductivity affacting factors is performed.Finally,according to the non-uniform distribution of the proppant and the distribution of the conductivity in each position of the fracture,a characterization method for the non-uniform distribution of the proppant is proposed,and a shale gas productivity model considering the settlement and non-uniform distribution of the proppant is established.The model analyzes pressure field distribution and production dynamic analysis under sensitive factors,and studies the distribution of residual gas under non-uniform distribution of proppants.By a combination of theoretical analysis and numerical simulation,the dissertation reveals the law of non-uniform distribution of proppants in complex fracture,and systematically evaluates the effectiveness of the fracture network,performs the post-fracturing effect evaluation considering proppant settlement and non-uniform distribution.The research results will provide theoretical basis and technical support for the efficient development of shale gas reservoirs.