An efficient numerical simulation of coupled thermal-hydro-mechanical process in CO2 leakage through fractured caprocks

Abstract:

The safety of CO₂ sequestration in geological formations relies on the integrity of the caprock. However, the elevated fluid pressure during CO₂ injection changes the stress states in the caprock, and may lead to reactivate pre-existing fractures or even fracture the caprock. It is necessary to develop an efficient and practical monitor technology to detect and identify CO₂ leakage pathways. To this end, we should understand the transport behavior of CO₂ coupled with geomechanical effects during injection. In this work, we first developed an efficient parallel fully-coupled thermal-hydro-mechanical simulator to model CO₂ transport in geological formations. The numerical model was verified through classical problems with analytical solutions. Then, based on this simulator, we investigated the fluid flow behavior when CO₂ leakage occurs through fluid-driven fracturing zones. We proposed an implicit, physics-based model to simulate the fluid-driven fracturing process by using several practical correlations, including fracturing pressure functions, porosity/permeability-stress relationships, which can be obtained by lab experiments. A set of numerical simulations have been conducted by considering various scenarios, such as different injection rates, locations and distributions of fracture zones, and initial fracture permeability. The numerical results show that there are several characteristics can be used to detect CO₂ leakage pathways, and it is possible to develop an advanced inverse modeling and monitoring technology to identify leakage locations, times and rates using measured pressure data of permanent downhole gauges and our simulator.