Abstract
Coupled THM (thermal-hydromechanical) processes have become increasingly important in studying the issues affecting subsurface flow systems. CO2 permeability of the fracture in caprock is a key factor that affects sealing efficiency of caprock. A new model associated with coupled THM processes that shows a good reliability was derived. Then, based on the COMSOL multiphysics software, a series of numerical calculations were performed on caprock models with a single fracture subject to coupled THM effects. Transmissivity of the fracture as a function of fracture angle, overburden pressure, fluid pressure difference, injected CO2 temperature, and the initial fracture aperture was elucidated, respectively. Average transmissivity of the fracture undergoes an increase by 1.74 times with the fracture angle (45°–90°), 2-3 orders of magnitude with the fluid pressure difference (5–30 MPa), and 4-5 orders of magnitude with the initial fracture aperture (0.05–0.5 mm), while it decreases by 3-4 orders of magnitude as overburden pressure increases from 30 to 80 MPa. Injected CO2 temperature has a small impact on the fracture permeability. This work provides an alternative tool to enrich the numerical modeling for the assessment of CO2 caprock sealing efficiency.
Highlights
To address the increasing concerns regarding carbon dioxide emission and its impact on climate change, CO2 geological sequestration has become a promising approach [1,2,3,4,5]
To reduce the atmosphere emissions, a large amount of CO2 is injected into the geological storage reservoirs, as shown in Figure 1, which may be gradually accumulated at the bottom of caprocks and lead to stress field changes in caprock
If the reservoir pressure is high enough to cause mechanical failure in caprock and connected pathways are created through fractures, a potential hazard of CO2 leakage will occur [6,7,8]
Summary
Several numerical calculations on caprock models with a single fracture subject to coupled THM effects were performed, and CO2 permeability of the fracture with respect to different fracture angle, overburden pressure, fluid pressure difference, injected CO2 temperature, and initial aperture was, respectively, evaluated. In this study, these models were calculated under simplified conditions of singlephase flow and heat conduction alone in thermal field for brevity
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