Simulation-based Research On Rock Deformation And Failure Process Under Water-Rock Coupling

The complication of water-rock coupling deformation and failure is the problem of damage and failure process of material and fluid turbulence in it, which is recognized as one of the physical and mechanical century challenges. The problem is not only the basis of scientific forefront and hot topic, but also the core content and the urgent need to resolve key issues in many applications, such as hydraulic fracturing. Meanwhile, hydraulic fracturing is also the core issues to be confronted in resources exploitation, energy development, and many other fields. Thus, water-rock coupling deformation and failure problem is in the centre of science and applied research with great significance. In this paper, using numerical simulation as the basic research methodology, under the background of specific problems and challenges in current researches, basically starting from systematical formation of effective analysis method and an implementation tool, the two frontier topics in hydraulic fracturing, i.e., hydraulic fracturing in glutenite and three dimensional whole-process simulation of hydraulic fracturing, are taken as the research objects, Not only in-depth awareness of regularity and characteristics of crack extension but also revealing the water rock coupled failure mechanism are taken as research objectives. Analysis of characteristic morphology and some key indexes under different stages of crack initiation, extension as well as interaction is mainly focused. In the view of the above points, the detailed study is undertaken in this dessertation. The main content has been completed is as follows:(1) Relying on RFPA (Realistic Failure Process Analysis) methods in rock failure process analysis developed from meso-scopic statistical damage theory, combine with the newly established consider micro element damage induced evolution model of permeability coefficient. Then, a three dimensional cylindrical model under constant head difference is analyzed for deformation and failure process. Compared with existing experimental results for the physical, the results in this paper better reflects undermine the basic characteristics of morphology, specimen in elastic deformation phase reduces, nonlinear deformation phase permeability increases the permeability and the brittle instability of permeability during suddenly surge in typical characteristics. Apparently, that demonstrate the analytical methods and theoretical models is feasible.(2) Overcome the water (seepage)-rock (deformation) full coupled equations with low-level FEM (Finite Element Method) solve divergence. Through quadrilateral area coordinate theory combined with the general principles of coordination and correction techniques, under the beginning of the principle of minimum potential energy partition, a new low-level parametric plane quadrilateral element was constructed. By carrying out extensive evaluation of the element, the results indicate that the new element is not only effective solution to overcome the divergence, but also excellent mechanical properties of solid, flexible (through parametricβadjustment). Meanwhile, to alleviate a finite element problem (constant strain patch test by the four node element in the performance of the bending problem of poor performance in bending of the element has failure to pass the patch test) also provides useful information.(3) As a classic topic in computational mechanics and the key technology of CAE (Computer Aided Engineering)/CAM (Computer Aided Manufacturing) software, the provide an extremely efficient improved symmetric overrelaxation preconditioned conjugate gradient method (SSOR-CG) to large-scale finite fast solution of linear equations. The algorithm contains the original convergence of the algorithm robustness and inherent parallelism. Ideally, be less nearly 50% computation amount than original algorithm for high performance computing, so the algorithm is inherently efficient operational. Test results in good examples to prove this point.(4) Under the situation of seldom to calculate the water-rock coupling deformation and failure until rupture the whole process of parallel application systems is a in China, based on the rock- water damage coupling mesoscopic statistical analysis methods, relied on the Windows platform to run the RFPA main frame with Linux platform of cluster development in a multi-level mixed-FEM-coupled parallel programs (modules), thus, a water rock damage evolution analysis of parallel coupled system was developed. By an analysis of specific examples of parallel FEM solver system performance, the results demonstrated starting rational process cases calculations can achieve the best results, the speedup is nearly linear with the high efficiency furthermore, the default precision is ten million degrees of freedom (300 million elements) seepage-stress coupling step of the calculation stable at around 200s. Finally, using the system separately on two different properties of rock specimen under uniaxial compression studies on fine simulations, numerical work can enriched awareness of the law based on brittle crack propagation and interaction of damage evolution process.(5) Widespread and systematic study of the conglomerate hydraulic fracturing mechanism for crack propagation and characteristics of the problem, and take different gravel content, gravel size, gravel mechanical properties and different confining stress levels into consideration. Focus on the effect of these factors on the model of crack pressure, breaking stress, cracks form and extend the impact of the law; In-depth analysis of the crack from the crack, the process of expansion and interaction of mechanical mechanism. Research on I, II type crack interaction conversion mechanism. Finally, through the establishment of the mechanical model of qualitative content, micro crack distribution and breaking pressure are researched during the influence of the gravel, gravel mechanical properties and different confining stress levels of the stress concentration.(6) Application for the water-rock coupling parallel analysis system, hydraulic fracturing process of full three-dimensional numerical simulation was done with a laboratory-scale model for four different stress states. The crack geometry with the stress state also reveal the inherent mechanism. In addition, further in-depth discussion of the three-dimensional crack propagation characteristics, influencing factors, instability, the relationship between hydraulic gradient, the acoustic emission rules and other issues will be continued down the road.