A Finite Volume Framework for Accurate Modeling of Fault Reactivation in Poroelastic Rocks

Abstract

Safe and sustainable exploitation of geo-energy resources requires not only a comprehensive evaluation of the performance and economics of the corresponding projects but also the assessments of the associated risks, including the risk of induced seismicity. Indeed, seismic events may arise from the reactivation of natural faults and fractures due to subsurface engineering activities. Numerous anthropogenic activities including geothermal energy production and CO2 geological storage have been identified as potential triggers of these seismic events. The risks associated with induced seismicity stem from the potential for surface movement, structural damage, and negative impacts on both the environment and human health. The corresponding risk assessments highly rely on geomechanical modeling which is progressively being integrated into the reservoir modeling workflows. This integration demands high levels of integrability, flexibility and performance from the computational engines employed. These requirements, along with the complexities of the underlying physical, numerical and implementation aspects severely constrain the availability of suitable computational capabilities. Increasing societal concerns about induced seismicity amplify the demand for such capabilities, highlighting a lack of efficient and comprehensive solutions in both academia and industry. This thesis contributes to bridging this gap through the development of an innovative modeling framework. Leveraging the ubiquity of Finite Volume Methods (FVM) in traditional reservoir simulations, the newly proposed FVM schemes for coupled fluid mass and momentum balance equations present an opportunity for seamless integration of geomechanical modeling into existing reservoir modeling frameworks. As a result, the proposed approach satisfies the aforementioned requirements and presents an accurate and efficient framework for the investigation of induced seismicity in geo-energy applications. The core innovation of the thesis is represented by fully implicit schemes of FVM for the coupled modeling of faulted poroelastic media implemented in the opensource Delft Advanced Research Terra Simulator (DARTS). The schemes are based on coupled multi-point flux and multi-point stress approximations derived from the local conservation of fluid mass and forces. They support arbitrary material heterogeneity, anisotropy, boundary conditions, fluid properties, and friction laws. To further improve the performance of coupled modeling, block-partitioned preconditioning strategy has been implemented. Besides, first-of-its-kind nonlinear scheme of FVM for the pure elasticity problem has been proposed and implemented in DARTS...