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What Induced Seismicity From CO2 Injection Can Tell Us About Fluid Migration Pathways

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip III

Type: Oral

Date: 4/20/2021

Presentation Time: 02:45 PM Pacific

Description: 

Monitoring of induced seismicity before, during, and after injection of super-critical CO2 is being used to help determine pathways the fluid takes during migration over time and to assess the risk of felt seismicity the Illinois Basin – Decatur Project (IBDP). The microseismic activity at the site primarily indicates locations where existing fractures and faults were reactivated. Some microseismic events were large enough to determine focal mechanisms, but no injection-related felt seismicity has been detected. Most of the induced seismicity occurs below the reservoir in fractured low porosity/permeability igneous basement rocks. The reservoir itself, the Cambrian Mt. Simon Sandstone, has high porosity and permeability, with much less common fracturing and faulting. The temporal development of the microseismicity at IBDP indicates stress perturbations that migrate to the north and west of the injection location, concentrated in elongated clusters with NE-SW orientations. Horizontal fluid migration occurring in the Mt. Simon sandstone could be the dominant pathway for transmission of fluid and pressure away from the injection well to locations that are hydrologically connected to the basement rocks. To address the potential of upward migration of fluid pressure to cause slip on faults in overlying rocks that could lead to loss of top seal integrity, microseismic monitoring was combined with measurements of pressure and chemistry from subsurface monitoring wells. Shallow monitoring at the site surface has confirmed no CO2 leakage to the surface. We suggest that that fluid directional pathway is either accommodated by horizontal migration within the Mt. Simon, or by open fractures in the basement with orientations that connect the NE-SW oriented reactivated faults. We use this integrated data set to create a fault and fracture model that is consistent with the interpretation of the seismic reflection data and the observed microseismicity as a basis on which to test the potential for induced slip on existing fault planes and the risk for induced felt seismicity.

Presenting Author: Sherilyn Williams-Stroud

Student Presenter: No

Authors