In this dissertation, two new numerical approaches for hydraulic fracturing in tight reservoir were developed. A more physical-based numerical 3D-model was developed for simulating the whole hydraulic fracturing process including fracture propagation, closure and contact as well as proppant transport and settling. In this approach rock formation, pore and fracture systems were assembled together, in which hydro-mechanical coupling effect, proppant transport and settling as well as their influences on fracture closure and contact were fully considered. A combined FDM and FVM schema was used to solve the problem. Three applications by using the new approach were presented. The results illustrated the whole hydraulic fracturing process well and seemed to be logical, which confirmed the ability of the developed approach to model the in-situ hydraulic fracturing operation from injection start till fully closure. In order to investigate the orientation problem of hydraulic fracturing in tight reservoir, a new approach for simulating arbitrary fracture propagation and orientation in 2D was developed. It was solved by a hybrid schema of XFEM and FVM. Three numerical studies were illustrated, which proved the ability of the developed approach to solve the orientation problem in field cases.

Hydraulic fracturing in combination with horizontal well is playing a key role in the efficient development of unconventional gas/oil reservoirs and deep geothermal resources. However, the integral operation, especially from the perspective of THM (Thermal-Hydraulic-Mechanic) interactions have not been studied systematically. In this thesis, targeted improvements were achieved through developing a series of mathematical/physical models, and their implementation into the existing numerical tools (FLAC3Dplus and TOUGH2MP-FLAC3D), including: (a) a new thermal module for FLAC3Dplus based entirely on the finite volume method (FVM), which is especially developed for the fracturing process and can also achieve the modeling of gel breaking; (b) a rock damage module of TOUGH2MP-FLAC3D, which also considers the impacts of rock damaging process on evolution of permeability; (c) an in-depth improved FLAC3Dplus simulator that obtains the ability to simulate a 3D fracture propagation with arbitrary orientation. After the corresponding verifications, the improved tools were applied in different case studies to reveal: a) influences of the fluid’s viscosity on the fracturing results in tight sandstone reservoirs; b) the induced seismicity during the fracturing operation and the reactivation of the natural faults; and c) the fracture propagation with arbitrary orientation.

Geomechanics and Geodynamics of Rock Masses – Selected Papers contains selected contributions from EUROCK 2018, the 2018 International Symposium of the International Society for Rock Mechanics (ISRM 2018, Saint Petersburg, Russia, 22—26 May 2018). Dedicated to recent advances and achievements in the fields of geomechanics and geotechnology, the book will be of interest to researchers and professionals involved in the various branches of rock mechanics and rock engineering. EUROCK 2018, organized by the Saint Petersburg Mining University, is a continuation of the successful series of ISRM symposia in Europe, which began in 1992 in Chester, UK.

In this dissertation, two specific numerical models have been developed to address the issues associated with utilization of supercritical CO2, like fracture creation, proppant placement and fracture closure in unconventional gas reservoirs, reservoir stimulation, heat production and CO2 sequestration in deep geothermal reservoirs, respectively. In unconventional gas reservoir, the model consisting of classic fracture model, proppant transport model as well as temperature-sensitive fracturing fluids (CO2, thickened CO2 and guar gum) has been integrated into the popular THM coupled framework (TOUGH2MP-FLAC3D), which has the ability to simulate single fracture propagation driven by different fracturing fluids in non-isothermal condition. To characterize the fracture network propagation and internal multi fluids behavior in deep geothermal reservoirs, an anisotropic permeability model on the foundation of the continuum anisotropic damage model has been developed and integrated into the popular THM coupled framework (TOUGH2MP-FLAC3D) as well. This model has the potential to simulate the reservoir stimulation and heat extraction based on a CO2-EGS concept.

Enhanced geothermal systems (EGSs) evolved from the hot dry rock can provide a significant amount of energy while shifting towards negligible carbon emission. In order to investigate some important issues related to EGS, several scenarios have been analyzed using powerful numerical tools (FLAC3Dplus and TOUGH2MP-TMVOC). While conducting multiple hydraulic fracturing, it is observed that the newly created successive fracture’s configuration highly depends on the previous one under the influence of stress shadow. Therefore, the assumption of using similar multiple fracture geometries and shapes for energy exploitation may lead to erroneous estimations. A case study has been performed further using the engineering data of the GeneSys project in the North German Basin. Numerous scenarios have been investigated, and the optimized EGS project is proposed, whose installed power capacity of one side of the injection well declines from 7.17 MW to 5.08 MW over 30 years. Moreover, the Levelized cost of electricity is calculated at 5.46 c$/kWh, which is quite economical compared to the current electricity price. Finally, an innovative concept of regenerative EGS is proposed by storing surplus renewable energy in multiple hydraulic fractures that can reduce the reservoir temperature reduction rate. The results of continuous injection/production cycles depicted that a regenerative EGS could be achieved in reality.

Hydraulic fracturing is essential technology for the development of unconventional resources such as tight gas. So far, there are no numerical tools which can optimize the whole process from geological modeling, hydraulic fracturing until production simulation with the same 3D model with consideration of the thermo-hydro-mechanical coupling. In this dissertation, a workflow and a numerical tool chain were developed for design and optimization of multistage hydraulic fracturing in horizontal well regarding a maximum productivity of the tight gas wellbore. After the verification a full 3D reservoir model is generated based on a real tight gas field in the North German Basin. Through analysis of simulation results, a new calculation formula of FCD was proposed, which takes the proppant position and concentration into account and can predict the gas production rate more accurately. However, not only FCD but also proppant distribution and hydraulic connection of stimulated fractures to the well, geological structure and the interaction between fractures are determinant for the gas production volume. Through analysis the numerical results of sensitivity analysis and optimization variations, there is no unique criterion to determine the optimal number and spacing of the fractures, it should be analyzed firstly in detail to the actual situation and decided then from case to case.

This book mainly focuses on the adaptive analysis of damage and fracture in rock, taking into account multiphysical fields coupling (thermal, hydro, mechanical, and chemical fields). This type of coupling is a crucial aspect in practical engineering for e.g. coal mining, oil and gas exploration, and civil engineering. However, understanding the influencing mechanisms and preventing the disasters resulting from damage and fracture evolution in rocks require high-precision and reliable solutions. This book proposes adaptive numerical algorithms and simulation analysis methods that offer significant advantages in terms of accuracy and reliability. It helps readers understand these innovative methods quickly and easily. The content consists of: (1) a finite element algorithm for modeling the continuum damage evolution in rocks, (2) adaptive finite element analysis for continuum damage evolution and determining the wellbore stability of transversely isotropic rock, (3) an adaptive finite element algorithm for damage detection in non-uniform Euler–Bernoulli beams with multiple cracks, using natural frequencies, (4) adaptive finite element–discrete element analysis for determining multistage hydrofracturing in naturally fractured reservoirs, (5) adaptive finite element–discrete element analysis for multistage supercritical CO2 fracturing and microseismic modeling, and (6) an adaptive finite element–discrete element–finite volume algorithm for 3D multiscale propagation of hydraulic fracture networks, taking into account hydro-mechanical coupling. Given its scope, the book offers a valuable reference guide for researchers, postgraduates and undergraduates majoring in engineering mechanics, mining engineering, geotechnical engineering, and geological engineering.