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.

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.

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.

This book presents the coupled Thermo-Hydro-Mechanical-Chemical (THMC) processes in fractured rocks at varying scales from single fractures to fracture networks. It also discussed the implication and potential application of the advanced understanding of coupled THMC processes in fractured rocks for geotechnical and geo-energy engineering.

Among the most important and exciting current steps forward in geo-engineering is the development of coupled numerical models. They represent the basic physics of geo-engineering processes which can include the effects of heat, water, mechanics and chemistry. Such models provide an integrating focus for the wide range of geo-engineering disciplines. The articles within this volume were originally presented at the inaugural GeoProc conference held in Stockholm and contain a collection of unusually high quality information not available elsewhere in an edited and coherent form. This collection not only benefits from the latest theoretical developments but also applies them to a number of practical and wide ranging applications. Examples include the environmental issues around radioactive waste disposal deep in rock, and the search for new reserves of oil and gas.

Anthropogenic greenhouse gas emissions, energy security and sustainability are three of the greatest contemporary global challenges today. This year the Sino-German Cooperation Group “Underground Storage of CO2 and Energy”, is meeting on the 21-23 May 2013 for the second time in Goslar, Germany, to convene its 3rd Sino-German conference on the theme “Clean Energy Systems in the Subsurface: Production, Storage and Conversion”. This volume is a collection of diverse quality scientific works from different perspectives elucidating on the current developments in CO2 geologic sequestration research to reduce greenhouse emissions including measures to monitor surface leakage, groundwater quality and the integrity of caprock, while ensuring a sufficient supply of clean energy. The contributions herein have been structured into 6 major thematic research themes: Integrated Energy and Environmental Utilization of Geo-reservoirs: Law, Risk Management & Monitoring CO2 for Enhanced Gas and Oil Recovery, Coal Bedded Methane and Geothermal Systems Trapping Mechanisms and Multi-Barrier Sealing Systems for Long-Term CO2 Storage Coupled THMC-Processes and Numerical Modelling Rock Mechanical Behaviour Considering Cyclic Loading, Dilatancy, Damage, Self-sealing and Healing Underground Storage and Supply of Energy “Clean energy systems in the subsurface” will be invaluable to researchers, scientists and experts in both academia and industry trying to find a long lasting solution to the problems of global climate change, energy security and sustainability.

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