Effects of the Earth Characteristics on Induced Seismicity Potential

Abstract

AbstractThe increase in wastewater disposal associated with hydraulic fracturing, and other subsurface fluid injection and production (SFIP) operations as well as the heightened public concern regarding possible induced seismicity, have propelled us to study the related issues. In this work, we investigate induced seismicity caused by pore-pressure changes due to fluid injection. We use a reservoir simulator to model the pore-pressure change in a realistic case with different injection and production scenarios. This research shows that the presence of critical faults and the net injected volume are among the most important risk factors contributing to induced seismicity. Reservoir characteristics such as geometry, size, and permeability are identified as the main components that pertain to reservoir pressure response, causing critical pore-pressure increase and subsequent potential seismicity. We apply our method to the Central Illinois Basin, which is a primary candidate for CO2 Sequestration, and observe that the pressure changes differ widely, but can easily lead to fault instability and seismic activity up to 10 km away from the injection well. The magnitude of pressure increase and the geometry of the affected area greatly depends upon the permeability structure of the injection formation and surroundings. Further, we define the required pore-pressure buildup for fault instability. In addition, we generate a random distribution of faults in the area of interest where they have a certain distribution for required pore-pressure buildup for fault slip (criticality). Earthquake magnitudes are sampled from a distribution following Guttenberg-Richter law. We introduce a simple homogeneous, isotropic representation for the reservoir in order to study the primary parameters that affect the frequency and magnitude of induced seismic events. Given the absence of a physics-based method for induced seismicity risk assessment, this paper proposes a novel approach for said risk assessment, and can be used to mitigate the fault reactivation risk.