Mathematical Modelling of Fault Reactivation Induced by Water Injection

Thanh Son Nguyen,Yves Guglielmi,Bastian Graupner,Jonny Rutqvist

doi:10.3390/min9050282

Abstract

Faults in the host rock that might exist in the vicinity of deep geological repositories for radioactive waste, constitute potential enhanced pathways for radionuclide migration. Several processes might trigger pore pressure increases in the faults leading to fault failure and induced seismicity, and increase the faults’ permeability. In this research, we developed a mathematical model to simulate fault activation during an experiment of controlled water injection in a fault at the Mont-Terri Underground Research Laboratory in Switzerland. The effects of in-situ stress, fault shear strength parameters and heterogeneity are assessed. It was shown that the above factors are critical and need to be adequately characterized in order to predict the faults’ hydro-mechanical behaviour.

Highlights

Subsurface fluid injection is an operational practice associated with many industrial activities, such as; (i) disposal of wastewater by injection into deep formations; (ii) injection of water or CO2 into depleted reservoirs for enhanced oil recovery; (iii) hydraulic fracturing to enable production of oil and gas from low-permeability reservoirs; (iv) injection of supercritical CO2 into deep formations for permanent carbon capture and storage; and (v) injection into geothermal reservoirs to replenish water lost to steam production or to develop enhanced geothermal systems
We focus on an experiment performed in a natural fault in Opalinus Clay, at the Mont-Terri Underground Research Laboratory (URL), Switzerland
In this this research research we we developed developed aa mathematical mathematical model model for for fault fault reactivation reactivation due pressure increase, based on the classical theory of poromechanics and Coulomb’s friction

Summary

Introduction

Subsurface fluid injection is an operational practice associated with many industrial activities, such as; (i) disposal of wastewater by injection into deep formations; (ii) injection of water or CO2 into depleted reservoirs for enhanced oil recovery; (iii) hydraulic fracturing (fracking) to enable production of oil and gas from low-permeability reservoirs; (iv) injection of supercritical CO2 into deep formations for permanent carbon capture and storage; and (v) injection into geothermal reservoirs to replenish water lost to steam production or to develop enhanced geothermal systems. In Oklahoma, the rate of occurrence of events with magnitudes (M) larger than 3, with some larger than 5, has become greater than in California Factors such as the rate, duration, pressure and aerial extent of the injection as well as the geological setting contribute to the potential of fault reactivation around the injection area leading to increased seismicity [2]. Another area of activity where mechanical and fluid transport processes in faults need to be assessed is the geological disposal of high-level waste (HLW). In the very long time frame associated with the DGR, Minerals 2019, 9, 282; doi:10.3390/min9050282 www.mdpi.com/journal/minerals

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