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.

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.

The subject of thermo-hydro-mechanical coupled processes in fractured rock masses has close relevance to energy-related deep earth engineering activities, such as enhanced geothermal systems, geological disposal of radioactive waste, sequestration of CO2, long-term disposal of waste water and recovery of hydrocarbons from unconventional reservoirs. Despite great efforts by engineers and researchers, comprehensive understanding of the thermo-hydro-mechanical coupled processes in fractured rock mass remains a great challenge. The discrete element method (DEM), originally developed by Dr. Peter Cundall, has become widely used for the modeling of a rock mass, including its deformation, damage, fracturing and stability. DEM modeling of the coupled thermo-hydro-mechanical processes in fractured rock masses can provide some unique insights, to say the least, for better understanding of those complex issues. The authors of this book have participated in various projects involving DEM modeling of coupled thermo-hydro-mechanical processes during treatment of a rock mass by fluid injection and/or extraction and have provided consulting services to some of the largest oil-and-gas companies in the world. The breadth and depth of our engineering expertise are reflected by its successful applications in the major unconventional plays in the world, including Permian, Marcellus, Bakken, Eagle Ford, Horn River, Chicontepec, Sichuan, Ordos and many more. The unique combination of the state-of-the-art numerical modeling techniques with state-of-the-practice engineering applications makes the presented material relevant and valuable for engineering practice. We believe that it is beneficial to share the advances on this subject and promote some further development.

Science of Carbon Storage in Deep Saline Formations: Process Coupling across Time and Spatial Scales summarizes state-of-the-art research, emphasizing how the coupling of physical and chemical processes as subsurface systems re-equilibrate during and after the injection of CO2. In addition, it addresses, in an easy-to-follow way, the lack of knowledge in understanding the coupled processes related to fluid flow, geomechanics and geochemistry over time and spatial scales. The book uniquely highlights process coupling and process interplay across time and spatial scales that are relevant to geological carbon storage. - Includes the underlying scientific research, as well as the risks associated with geological carbon storage - Covers the topic of geological carbon storage from various disciplines, addressing the multi-scale and multi-physics aspects of geological carbon storage - Organized by discipline for ease of navigation

In this dissertation, three simulators (i.e. TOUGH2MP, TOUGHREACT and FLAC3D) were used to simulate the complex physical and chemical interactions induced by CO2 sequestration. The simulations were done instages, ranging from the two phase (water and CO2) fluid flow (H2), through coupled hydro-mechanical effects (H2M) and geochemical responses (i.e. CO2-water-rock interactions (H2C)), to the extension of CCS to CCUS by the application of combined geothermal production and CO2 sequestration technologies. The findings of this study are essential for a thorough understanding of the complex interactions in the multiphase, multicomponent porous media controlled by different physical and chemical mechanisms. Furthermore, the simulation results will provide an invaluable reference for field operations in CCS projects, especially for the full-integration pilot scale CCS project launched in the Ordos Basin. Subsequently, a preliminary site selection scheme for the combined geothermal production and CO2 sequestration was set up, which considered various factorsinvolved in site selection, ranging from safety, economical, environmental and technical issues. This work provides an important framework for the combined geothermal production and CO2 sequestration project. However, further numerical and field studies are still needed to improve on a series of criteria and related parameters necessary for a better understanding of the technology.

Understanding Faults: Detecting, Dating, and Modeling offers a single resource for analyzing faults for a variety of applications, from hazard detection and earthquake processes, to geophysical exploration. The book presents the latest research, including fault dating using new mineral growth, fault reactivation, and fault modeling, and also helps bridge the gap between geologists and geophysicists working across fault-related disciplines. Using diagrams, formulae, and worldwide case studies to illustrate concepts, the book provides geoscientists and industry experts in oil and gas with a valuable reference for detecting, modeling, analyzing and dating faults. - Presents cutting-edge information relating to fault analysis, including mechanical, geometrical and numerical models, theory and methodologies - Includes calculations of fault sealing capabilities - Describes how faults are detected, what fault models predict, and techniques for dating fault movement - Utilizes worldwide case studies throughout the book to concretely illustrate key concepts

In this thesis a parallel simulation platform, namely TOUGH2MP-FLAC3Dplus, was further developed by linking the multiphase multicomponent flow code TOUGH2MP and the further developed geomechanical code FLAC3Dplus for large-scale simulation of the coupled THM/C processes related to geo-energy production. A series of mathematical/physical models were developed and implemented in this platform, including (1) an improved equation of state for CO2-CH4-H2O-NaCl system which considers the effect of salt on phase partition and fluid properties in gas reservoirs; (2) a modified coupling approach for the simulation of hydraulic fracturing in tight geo-reservoirs, which considers the multiphase multicomponent leakoff effects; (3) a thermo-hydro-mechanical model based on a crack tensor for naturally fractured rock masses and faults. All these verified models have been applied in three different case studies, including CO2 enhanced gas recovery (EGR) in the Altmark natural gas field; (2) Hydraulic fracturing in three different types of geo-reservoirs (tight gas, oil and geothermal reservoir); (3) Geothermal energy utilization induced seismicity in Unterhaching. The developed models and the numerical platform can be used to predict the coupled THM/C behavior of rock formations, to optimize the CO2-EGR and hydraulic fracturing in tight geo-reservoirs, as well as reduce the geo-risks related to geo-energy production.