Application of hybrid numerical and analytical solutions for the simulation of coupled thermal, hydraulic, mechanical and chemical processes during fluid flow through a fractured rock

Abstract

In many subsurface engineering geoscience applications the impact of thermal, hydraulic, mechanical and chemical (THMC) processes needs to be evaluated. Coupled process models require solution of the partial differential equations describing energy or mass balance. Ignoring the coupling of these processes can lead to a significant oversimplification which may not adequately represent the systems being modelled. Incorporation of coupled processes and associated phenomena inevitably leads to numerical stability issues due to very different scales in terms of spatial distribution, time and parametrical heterogeneity. One approach to simplify the computational demands is to integrate analytical and physical models into standard numerical modelling techniques (in this case finite elements), effectively adding sub-grid scale and sub-time scale information to the model. We present such an approach for the simulation of fluid flow through a fracture validated against experimental data and cross comparison with results of other modelling teams within the DECOVALEX 2015 (development of coupled models and their validation against experiments) project (http:// www.decovalex.org). By replacing the mechanical behaviour and chemical transport processes with physical models, and by utilising the static nature of the temperature changes, only the hydraulic system required numerical solution in a highly coupled problem. Physical models for fracture closure due to pressure solution, fracture opening due to chemical dissolution, the development of channel flow and a change in the reactive transport characteristics with time were implemented and are described here. The main features of the experimental data could be replicated, although lying outside of the parameter range suggested by the literature. Comparison with other teams using different modelling approaches indicated internal consistency.

Experimental and Numerical Modelling of Nonlinear Flow Behavior in Single Fractured Granite

“…Since gas is strongly compressible, the flow rate within the fracture is different from the rate measured at the outlet and the Forchheimer equation is inadequate to be directly used to fit the experimental data. However, the Forchheimer equation can be written as equation (4). Based on the mass conservation theorem and the ideal gas law under isothermal condition, equations (5) and (6) can be obtained, respectively.…”

“…An accurate understatement of fluid flow through fractured rock is crucial in many science and engineering situations, including extraction of geothermal energy, recovery of oil and natural gas, geologic sequestration of CO 2 , development of unconventional shale gas, coalbed methane reserves, and storage of radioactive waste [1][2][3][4][5][6]. One area of this field that attracts significant interest is the hydromechanical responses of rock fractures.…”

“…(a) 3D surface topography for both sides and (b) contact state of different samples 4. Geofluids effectively characterize nonlinear flow processes at the macroscopic level without focusing on the transition from linear to nonlinear flow:…”

Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Permeability Evolution in a CO2-Circulated Geothermal Reservoir

“…Based on experimental studies, several numerical studies have quantified the significant contribution of coupled THMC processes to EGS reservoir production decline. Pressure solution and chemical precipitation are found to be key mechanisms for permeability reduction in fractures [17][18][19][20], while chemical dissolution may increase permeability [21]. The strong temperature dependence of precipitation/dissolution kinetics of minerals also exerts significance on permeability evolution [22,23].…”

Numerical Simulation of Solute Transport in Fractured Rock with Particle Tracking Method

“…Numerous studies have been carried out in this area by means of both laboratory experiments and numerical simulations ( [1]- [4]). It has been proved that varies of factors, e.g., the surface roughness and fracture aperture statistics may have some influences on the groundwater flow and solute transport processes during the numerical simulation ( [5]- [7]). In these studies fractures are treated in several different ways: some researchers studied the seepage flow in single rock fracture ([8]- [13]); some considered the fracture and the matrix as a continuum ([14]- [16]); some developed the models under the consumption of dual-porosity/permeability ( [17]- [20]); and some utilized the fracture network system to generate stochastic fracture models ( [21]- [25]).…”