Geomechanical Limitations on Geological Carbon Sequestration in the Cambrian Strata of Southwestern Ontario

Geological Carbon Sequestration (GCS) is viable within the Cambrian sandstone reservoir of southwestern Ontario but GCS will likely be limited in sequestration capacity and CO2 injectivity. Capacity and injectivity limitations will arise during CO2 injection because of the fluid-pressure responses induced within the Cambrian reservoir and the subsequent geomechanical-hydrogeological responses in the Precambrian basement. Any coupling between a pressurized reservoir overlying a critically stressed Precambrian basement can be expected to cause local microseismicity. In this context, the challenge is to optimize CO2 injection while minimizing microseismic responses. The principal risks and responses to the development of the Cambrian sandstone that must be resolved beforehand are (i) the robust estimation of accessible pore space for the injected super-critical CO2; (ii) the limitation of the potential for fracturing or shear damage to the caprock that might allow leakage; (iii) the induced failure of seals in active, suspended or legacy oil and gas wells penetrating the reservoir allowing upward brine or CO2 migration; (iv) the buoyant transmission of CO2 along permeable or unclamped faults penetrating the reservoir; and, (v) any microseismicity induced by pressure increases penetrating critically-stressed basement rocks. Notwithstanding these risks, we believe the Cambrian sandstone is a viable CO2 reservoir for at least 10 megatonnes of CO2 sequestration annually.The Ontario Government’s 2018 goal of 30% CO2 emissions reduction by 2030 must partly occur though industrial sequestration of CO2 within the Cambrian reservoir. However, to provide information critical for regulatory management of GCS, research is needed immediately to pave the way for CO2 injection operations if they are to have any role in industrial decarbonization. This article summarizes our weak understanding of these critical issues and proposes the development of a research borehole to provide much of the necessary information for regulatory management of CO2 injection. It will also aid the design and operation of CO2 injection hubs along the north shore of Lake Erie. In short, a site similar to the Aquistore site is needed for development of the Cambrian GCS reservoir in southwestern Ontario.