Coupled THMC Processes Research Articles

Thermo-hydro-mechanical-chemical coupling in chalk reservoirs: Impact on fluid flow and deformation during water injection

Reliable prediction of the rate- and fluid-dependent evolution of elasto-plastic strain in chalk is essential to minimize the risk associated with sea-floor subsidence and subsurface deformation. Experimental observations show that physicochemical interaction between the aqueous solutions and rock surface causes the change of mechanical properties in chalk. Here, we quantify the experimental observations of hydrostatic pore collapse strength and bulk modulus of water-saturated chalk specimens as a function of temperature and sulfate concentration. Further, a wrapper is developed to couple the non-isothermal transport of the multi-phase flow simulator with the geomechanics simulator to consider the impact of the coupled interactions on fluid transport and reservoir deformation. In this study, the interplay between thermo-hydro-mechanical-chemical processes in chalk reservoirs is investigated by means of numerical experiments. Computational results suggest that reservoir pressure depletion, temperature changes, and water weakening play significant roles in controlling the reservoir's deformation and production. Our study also confirms that accounting explicitly for the coupled THMC processes in reservoir simulations of water flooding in chalk is required for reliable prediction of reservoir responses.

The Coupled THMC finite-element modeling of hydrothermal systems: Insights into the Jiama porphyry metallogenic system

The formation and localization of hydrothermal ore deposits largely depend on coupled thermal–hydraulic–mechanical–chemical processes (called coupled THMC processes) in a porphyry metallogenic system. However, these processes and the hydrodynamics of porphyry metallogenic systems remain unclear. In this study, we developed two-dimensional coupled THMC finite-element models to simulate the spatiotemporal evolutions and interactions among the temperature, pore pressure, deformation, and migration of Cu in the Jiama Cu-polymetallic porphyry metallogenic system and to investigate the hydrodynamic mechanisms based on the geology of this deposit. The results show that the low-permeability upper layer of the wall rock, inhomogeneous thermal expansion, and continuous and multiple intrusions of magma induce an abnormally high pore fluid overpressure zone above the Jiama porphyry intrusion. The high overpressure zone and its evolution above the porphyry intrusion play key roles in the formation of the hydrothermal metallogenic system. First, the evolution of the overpressure changes the fluid flow patterns during different periods of the hydrothermal metallogenic system, that is, the outward flow from the porphyry in the early stage and the backflow towards the porphyry in the late stage. These two different flow patterns are consistent with the observations of mineral growth bounds and unidirectional solidification textures. Second, the high overpressure leads to the appearance and development of fractures above the intrusion. These fractures conform to the ore-bearing spaces of the hornfels and porphyry orebodies above the intrusion. Finally, the evolution of the overpressure can be used to predict the Cu concentration in interlayer detachment zones, which is consistent with geological observations based on which the interlayer detachment zones contain skarn orebodies. In this study, an overpressure-driven hydrodynamic process of a hydrothermal metallogenic system is illustrated, physical and mechanical explanations for geological observations in the Jiama porphyry metallogenic system are provided, and the advantages of numerical simulations in studies of complex multi-field coupled geological systems are highlighted.

A coupled THMC modeling application of cemented coal gangue-fly ash backfill

Cemented coal gangue-fly ash backfill (CGFB) is prepared by mixing coal gangue, fly ash, cement and water. The CGFB mixtures are filled into mined-out areas of coal mines for ground control and waste disposal. Once placed underground, the performance of CGFB is subjected to the thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes and THMC coupling effects. Understanding the coupled THMC influence on CGFB is crucial for predicting the behavior of CGFB. This paper develops a THMC coupling model to describe and analyze the coupled THMC processes that occur in CGFB. The developed model considers the courses of thermal conduction and convection, fluid flow, suction development, chemical shrinkage, thermal expansion, and binder hydration. The simulation and prediction results of the developed model are compared with the experimentally tested data from 3 case studies. Good agreement is found between the modeling results and experimental data, validating the capability of the developed model to well characterize the properties of CGFB under coupled THMC loadings. The modeling results can also contribute to a better design of stable, durable and environment-friendly CGFB structures.

The coupled non-isothermal, multiphase-multicomponent flow and reactive transport simulator OpenGeoSys–ECLIPSE for porous media gas storage

Numerical simulations are a viable tool to gain insights into complex coupled THMC processes prevailing in many geoscientific applications. In this work, a coupling approach for OpenGeoSys and ECLIPSE is presented, which combines the multiphase flow simulations of ECLIPSE with heat and reactive geochemical component transport simulations of OpenGeoSys. The coupled simulator is capable of dealing with multiphase-multicomponent systems with no specific limitations regarding the components used. Furthermore, thermal effects like the Joule–Thomson effect and geochemical feedback on fluid flow and mass transport are accounted for by the coupled simulator. The developed coupled code is validated in a series of benchmarks. It is found that the results of the coupled simulator are in very close agreement with those obtained from the reference simulations with the relative errors being smaller than 0.00001, 0.0002 and 0.003 % for phase pressures, saturations and component concentrations, respectively. Validation of the thermal coupling of the simulators shows the same good agreement, if no thermal feedback on fluid flow is considered with a maximum relative error of 0.0015 %. Including thermal feedback on fluid flow shows increased relative differences of up to 0.3 % due to the slightly different equations of states used in the simulators. Given the good accuracy of the validation runs, the coupled code can thus now be applied for reservoir simulations of coupled processes occurring in the subsurface.

Modeling of coupled THMC processes in porous media

For landfill monitoring and aftercare, long-term prognoses of emission and deformation behaviour are required. Landfills may be considered as heterogeneous porous soil-like structures, in which flow and transport processes of gases and liquids interact with local material degradation and mechanical deformation of the solid skeleton. Therefore, in the framework of continuous porous media mechanics a model is developed that permits the investigation of coupled mechanical, hydraulical and biochemical processes in municipal solid waste landfills.

Coupled thermo-hydro-mechanical–chemical behaviour of cemented paste backfill in column experiments: Part II: Mechanical, chemical and microstructural processes and characteristics

The evolution of coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) (THMC) properties of underground cemented paste backfill (CPB) has been studied by means of experiments with insulated–undrained high columns. This paper which compliments Part I (Ghirian and Fall, 2013), presents the mechanical, chemical and microstructural processes and characteristics. Two columns have been built and filled with a specific CPB mix and equipped with different sensors. The vertical deformation and drying shrinkage for a period of 150days are measured. Also, four other columns are cured for 7, 28, 90 and 150days and then small samples are taken out from the columns to investigate the evolution of unconfined compressive strength (UCS), shear strength parameters, microstructural properties, and pore fluid chemistry. The combined results of the two part experiment show that strongly coupled THMC processes control CPB behavior. This study has demonstrated that mechanical properties are coupled to chemical reactions due to cement hydration and temperature changes inside the columns. Also, suction development due to self-desiccation can significantly increase the uniaxial compressive strength values with time. Chemical analysis including ion concentration measurements with time has revealed that change in pore fluid concentration affects the refinement of pore voids, and thereby results in improvement in hydro-mechanical performance as well as microstructural evolution of the CPB. External environmental loading, such as surface evaporation, can affect the durability performance of CPB structures. The results show that there is degradation of strength following surface shrinkage as well as an increase in saturated hydraulic conductivity due to existence of micro-cracks. The obtained results support that coupled THMC effects should be taken into account in field conditions to understand CPB behavior where stronger interplay reactions take place.

Modeling of Coupled Thermo-Hydro-Mechanical Processes with Links to Geochemistry Associated with Bentonite-Backfilled Repository Tunnels in Clay Formations

This paper presents simulation results related to coupled thermal-hydraulic-mechanical (THM) processes in engineered barrier systems (EBS) and clay host rock, in one case considering a possible link to geochemistry. This study is part of the US DOE Office of Nuclear Energy's used fuel disposition campaign, to investigate current modeling capabilities and to identify issues and knowledge gaps associated with coupled THMC processes and EBS- rock interactions associated with repositories hosted in clay rock. In this study, we simulated a generic repository case assuming an EBS design with waste emplacement in hor- izontal tunnels that are back-filled with bentonite-based swelling clay as a protective buffer and heat load, derived for one type of US reactor spent fuel. We adopted the Barcelona basic model (BBM) for modeling of the geo- mechanical behavior of the bentonite, using properties corresponding to the FEBEX bentonite, and we used clay host rock properties derived from the Opalinus clay at Mont Terri, Switzerland. We present results related to EBS host-rock interactions and geomechanical performance in general, as well as studies related to peak temperature, buffer resaturation and thermally induced pressurization of host rock pore water, and swelling pressure change owing to variation of chemical composition in the EBS. Our ini- tial THM modeling results show strong THM-driven interactions between the bentonite buffer and the low- permeability host rock. The resaturation of the buffer is delayed as a result of the low rock permeability, and the fluid pressure in the host rock is strongly coupled with the temperature changes, which under certain circumstances could result in a significant increase in pore pressure. Moreover, using the BBM, the bentonite buffer was found to have a rather complex geomechanical behavior that eventually leads to a slightly nonuniform density distribu- tion. Nevertheless, the simulation shows that the swelling of the buffer is functioning to provide an adequate increase in confining stress on the tunnel wall, leading to a stabil- ization of any failure that may occur during the tunnel excavation. Finally, we describe the application of a pos- sible approach for linking THM processes with chemistry, focusing on the evolution of primary and secondary swelling, in which the secondary swelling is caused by changes in ionic concentration, which in turn is evaluated using a transport simulation model.