The practice of carbon capture and storage (CCS) is emerging as one of several key strategies to reduce carbon emissions in our fight against climate change. Long-term storage of carbon dioxide in deep geological formations offers a promising pathway to significantly reduce CO2 emissions, particularly for hard to abate industries. However, large-scale CCS projects come with the risk of induced seismicity – earthquakes triggered by human activities. Understanding and managing this operational risk is paramount to ensuring the long-term safety and stability of CCS projects.
Induced seismicity is a phenomenon that can be caused by a variety of activities that alter the stress state of the Earth’s crust. Of relevance to CCS, the practice of injecting fluids deep underground is a known cause of induced seismicity. While the occurrence and risk of induced seismicity are influenced by a complex interplay of factors – including the geological characteristics of the injection site, the volume and pressure of the injected fluids, and operational parameters – the correlation between fluid injection and triggered seismicity is well-documented in the oil and gas industry and in a number of geothermal projects.
The activation of seismic events is problematic for a number of reasons, including but not limited to:
Damage, Safety and Environmental Risks
Induced seismicity has the potential to cause public concerns as well as structural and environmental damage. This has led to litigation and repair costs as well as interruption of injection operations and in some cases suspension or cancellation of entire projects.
Public Perception
Induced earthquakes can generate fear and anxiety among local communities, leading to a loss of trust in the industries responsible. This can result in public opposition to projects, legal challenges and increased regulatory scrutiny, potentially hindering operations and future development.
Caprock Integrity and CO2 Containment
Depending on the geology of the storage complex the fault and fracture processes associated with induced seismic events have the potential to breach the sealing rock layers that keep the sequestered volumes underground. Compromised caprock layers put the entire concept of permanent sequestration and corresponding carbon credits at risk.
Economic Impacts
Project costs associated with repairing infrastructure damage, addressing legal challenges and managing public concerns can be substantial. Induced seismicity can also force project delays, operational restrictions, and decreased productivity, impacting a project’s economic viability. In extreme cases operations could be shut down indefinitely.
The occurrence of induced seismicity has been widely documented in conjunction with various injection operations, including in oil and gas production, geothermal energy generation and wastewater disposal. These experiences offer valuable insights that can accelerate the understanding and management of induced seismicity risks in CCS projects.
Key lessons learned from these projects to date include:
While the geomechanical processes involved in CO2 injection for permanent storage share similarities with other fluid disposal and storage activities, certain factors unique to carbon storage can amplify both the risk and consequences of induced seismic events. These include:
Seismicity monitoring is an integral part of a robust measure-monitor-verify (MMV) plan for CCS projects and is increasingly being mandated as part of regulations. It involves deploying a network of sensitive seismometers to detect, locate and analyze seismic events. The primary objectives of seismicity monitoring in the context of CCS are twofold: monitoring of the storage complex for both natural and induced seismicity to assess risks to the integrity of CO2 containment, and regional monitoring to manage seismic events that could be felt by communities and stakeholders at the surface, thereby posing a risk to the project's social license to operate.
A comprehensive approach to seismicity monitoring involves the systematic collection, analysis and interpretation of seismic data to understand and mitigate potential risks. These components break-down as follows:
Measure your Baseline and Assess Risk
Establish a robust baseline of the natural, pre-existing background of seismic activity in the project area through the deployment of a seismic monitoring network for a sufficient amount of time prior to the start of injection. Conduct thorough site characterization to identify potential fault zones and areas prone to induced seismicity.
Monitor Operations
Continuously monitor seismic activity during injection operations in real time, using an appropriate network of seismic stations. Analyze the recorded data to determine event magnitudes, locations and source mechanisms.
Plan your Response, Adapt and Verify
Establish predefined thresholds for seismic activity based on comprehensive risk and hazards assessments starting with regulatory requirements. Develop and implement response protocols to manage operations and mitigate risks if these thresholds are exceeded. Embrace adaptive management strategies, continuously reviewing and updating the monitoring and response plans based on observed seismicity and evolving understanding of subsurface conditions.
Adopting a proactive approach empowers operators to anticipate potential challenges and to take preventative measures to mitigate risks effectively. By implementing a comprehensive seismicity monitoring program, operators can:
Ultimately, seismicity monitoring is essential to ensuring the safe and stable operation of CCS projects, protecting significant financial investments, ensuring regulatory compliance and maintaining public confidence in this critical climate change mitigation strategy.