Geomechanical Issues Affecting Long-Term Storage of CO₂

Mark D. ZOBACK
Stanford University

Abstract: The next several decades pose enormous challenges, and opportunities, for the global oil and gas industry. While oil and gas will continue to be used for decades to come, it is now recognized that enormous quantities of CO₂ have to be stored in subsurface geologic formations to reach global decarbonization goals. International bodies, countries (including China and the U.S., the world’s two largest greenhouse gas emitters) and 25% of Fortune 500 companies have all established net-zero emission goals by mid-century. In this talk, I will focus on a number of geomechanical issues that have to be considered to ensure long-term storage efficacy. While it has been long recognized that changes in reservoir pressure should not exceed the pressure at which hydraulic fracturing might occur of seal formations, this presentation will focus on a number of other issues have not been sufficiently addressed. First, it is important to identify potentially active faults to limit the possibility that injection-related increases in pore pressure could induce seismic, or aseismic, slip on known faults. Also, as existing evidence shows that potentially active faults (and the damage zones that surround them) are permeable, the presence of potentially active faults represent possible leakage pathways that should be avoided, even when injection-related pressure changes are too small to induce fault slip. Second, when utilizing depleted oil and gas reservoirs for long-term storage of CO₂, it is important to understand both the mechanical changes of the reservoir rocks and the stress changes that resulted from depletion. Such knowledge is required to predict how pressure associated with CO₂ injection will affect the reservoir. Finally, from the perspective of induced seismicity, it is critically-important to identify reservoirs with both top seals and bottom seals to avoid pressure communication to potentially active faults in the basement.

Bio: Dr. Mark D. Zoback is the Benjamin M. Page Professor of Geophysics, Emeritus at Stanford University, where he was also the Director of the Stanford Natural Gas Initiative and Co-Director of the Stanford Center for Induced and Triggered Seismicity and the Stanford Center for Carbon Storage and Senior Fellow in the Precourt Institute for Energy. Dr. Zoback conducts research on in situ stress, fault mechanics, and reservoir geomechanics with an emphasis on shale gas, tight gas and tight oil production as well as CO2 sequestration. Dr. Zoback served on the Secretary of Energy Subcommittee on shale gas development and the National Academy of Engineering Committee that investigated the Deepwater Horizon accident. He is the author of two textbooks and the author/co-author of about 400 technical papers. His most recent book, Unconventional Reservoir Geomechanics, was written with Arjun Kohli, and published in 2019 by Cambridge University Press. Dr. Zoback has received a number of awards and honors including election to the U.S. National Academy of Engineering in 2011 and the Robert R. Berg Outstanding Research Award of the AAPG in 2015. He was the 2020 chair of the Society of Petroleum Engineers Technical Committee on Carbon Capture, Utilization and Storage.