| Recent years,the study of deformation,failure and cracking of rock mass under fluid-solid coupling has become a focus of underground engineering research.Hydraulic fracturing,which also plays an increasingly important role in the research area,such as underground oil and gas exploitation,disaster prevention and mitigation,is a process fracture initiation and propagation in the rock matrix induced by pressurized fluid.Thus,the rocking mechanism during the hydraulic fracturing process,the propagation process of fractured rock mass under hydraulic pressure,and the influence of hydraulic pressure on the mechanical properties of rock mass are drawn lots of attention.Since the extreme complexity of the fluid-field-rock-mass system,in most of the research,the flow field is always idealized as Darcy flow in order to simplify the calculation.However,in practice,non-Darcy flow is a common phenomenon in flow field in rock mass.Therefore,problems such as when non-Darcy flow occurs and how it influences on properties of rock mass also need to be solved urgently.In addition,as engineering rock mass is a kind of discontinuity,which contains a large number of discontinuities such as joints and cracks,and the properties of the rock mass are mainly regulated by these discontinuities.Therefore,the discontinuous deformation analysis(DDA)method proposed by Mr.Shi Genhua is undoubtedly one of the best choices to study the stability of jointed rock mass.In this dissertation,the laboratory test of hydrofracturing crack propagation under fluid-solid coupling has been carried out,and the crack propagating processes of the rock-like specimens with a pre-set fracture in hydraulic fracturing tests under different testing conditions have been obtained,and the failure mechanism of rock hydrofracturing has been analyzed.Then,based on the finite volume method,the calculating models of three different kinds of rocks are established,and the critical conditions of non-Darcy flow occurring and the value of non-Darcy flow factor ? in sandstone and carbonate are calculated on OpenFOAM platform.Based on these results,the governing equations of seepage field and stress field of Darcy-non-Darcy flow in the fractured rock mass is derived on the basis of DDARF.Then,the seepage stress coupling analysis model of fractured rock mass on DDARF platform is established by secondary development.On this basis,numerical simulation of hydrofracturing tests of the pre-cracked rock-like specimens have been carried out,and the correctness of the model has been confirmed by comparing with the laboratory test results.And finally,the application of this numerical method has been introduced.The main contents of this dissertation are included in the following:1)In order to observe the cracking process of fractured rock mass under the hydraulic condition,rock-like specimens with carbonate-like properties have been made,and a visual hydraulic sealing device was designed.On this basis,uniaxial fracturing tests have been carried out for rock specimens with through-fracture under different hydraulic pressures,and then the crack propagations of the rock specimens under these conditions,the failure law,stress-strain curve,as well as the influence of water on rock parameters were obtained.2)Hydraulic fracturing process and failure laws,and the influence of different external conditions on rock parameters during hydraulic fracturing of single fracture specimens under different confining pressures and different hydraulic loading rates were obtained by laboratory hydrofracturing tests.And the mechanism of rock hydrofracturing has been also analyzed.3)The critical Reynolds numbers and non-Darcy flow factor.?,of each were derived from substituting three pre-established models,the Beadpack model.Bentheimer sandstone model and Estaillades carbonate model into OpenFOAM.Then.compared the obtained results with the former researches and the analyzed the sensitivity of the simulation,the correctness and accuracy of the calculation results have been ensured.4)To overcome the shortcomings of DDARF.a coupling program between DDARF and HyperMesh has been established,via utilizing the powerful grid model building ability of HyperMesh,which could reduce the modeling process of DDARF and greatly improve the efficiency of DDARF pre-processing modeling.Aimed at refining the disadvantage that DDARF pre-processing modeling that cannot generate multi-scale grids,the HyperMesh2DDARF interface program could be used to generate the multi-scale grids model,which will improve the computational efficiency while ensuring the computational accuracy.5)On the basis of mechanical calculation principle and seepage analysis of fracture network,a coupling analysis model of seepage and stress in the fractured rock mass has been proposed.The influence of deformation of fractured rock mass on groundwater movement and the deformation and failure characteristics of fractured rock mass under the seepage field and stress field were studied.In this dissertation,the equivalent of aperture of fracture under hydraulics was determinate,and the governing equations of Darcy and non-Darcy flow have been deduced and then these two equations were written into the program of DDARF.6)According to the DDARF-based seepage-stress coupling analysis model proposed previously,the fluid-solid coupling analysis of fractured rock with inner hydraulic pressure has been carried out.And the fracturing process and failure law of the single-flaw specimens with different initial confining stresses and hydraulic loading rates have been simulated by with and without considering the influence of non-Darcy flow model,respectively.These showed that the results obtained by simulated with the influence of non-Darcy flow are much more approachable to the laboratory testing result than that obtained by without considering the non-Darcy flow,which shows that the calculation method is reasonable and feasible,and can simulate the fracture process of specimens under hydraulic pressure very well.7)Based on DDARF fluid-solid coupled analysis model,the cracking of fractured rock-like specimens under different hydraulic loading rates have been calculated.The variations of initial and peak strength of rock specimens under different hydraulic loading rates in hydraulic fracturing were studied.8)The multi-scale grids rock models with pre-fabricated water injection cracks in different geometric shapes have been established by HyperMesh2DDARF program.The corresponding confining stress was applied around the rock by confining pressure.The hydrofracturing of underground rocks with prefabricated water injection cracks in different geometric shapes have been carried out.It shows that under non-Darcy flow a shorter and wider fracture geometry provides better productivity than a longer and narrower fracture;conversely,for Darcy flow,a longer and narrower fracture yields higher productivity. |
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