Collocated Finite Volume Scheme for Scalable Simulation of Induced Seismicity

An increasing number of geo-energy applications require the quantitative prediction of hydromechanical response in subsurface. Integration of mass, momentum, and energy conservation laws becomes essential for performance and risk analysis of enhanced geothermal systems, stability assessment of CO2 sequestration and hydrogen storage, resolving the issue of induced seismicity. The latter problem is of particular interest because it exposes safety risks to people and surface infrastructure.

Implicit coupling of conservation laws is computationally demanding and the solution procedure often uses different numerical methods for different laws that complicates simulation. Recently developed Finite Volume (FV) schemes for poromechanics present a unified approach for the modeling of conservation laws in geo-energy applications. Contact mechanics at faults requires special attention due to the inequality constraints it imposes and nonlinear friction laws that strongly affect the occurrence of seismicity.

We develop a cell-centered FV scheme for the purpose of integrated simulation in Delft Advanced Research Terra Simulator (DARTS) platform. The scheme proposes a unified numerical framework capable to resolve conservation laws in a fully implicit manner using a single collocated grid. Coupled multi-point flux and multi-point stress approximations provide mass, momentum, and heat fluxes at the faces of the computational grid. We use a conformal discrete fracture model to incorporate faults, where the multi-point approximations of fluxes respect the discontinuity in displacements. The block-partitioned preconditioner that takes the advantage of linear structure of the coupled problem is developed to facilitate the performance of the simulation.

The proposed numerical scheme are validated against analytical and numerical solutions in a number of test cases. The convergence and stability of the schemes are investigated. It is found that the developed scheme is indeed accurate, stable, and efficient. Thereafter, we demonstrate the applicability of the approach to model fault reactivation at the laboratory scale. In a core injection test, we validate the results of simulation against experimental measurements. Next, we investigate the performance of the different preconditioning strategies. The proposed block-partitioned preconditioning strategy demonstrates the scalability and efficiency of the numerical framework.