Creties D. Jenkins, Pieter Pestman, Rose and Associates
A thorough subsurface characterization is critical for quantifying the storage capacity, injectivity and containment potential of a CCUS project and identifying associated risks. If this characterization fails to provide an accurate understanding (due to limited data, improper assumptions, or unrepresentative models) then the CCUS project can be jeopardized. In this respect, it is useful to consider past injection projects that have failed, and what we can learn from them.
While subsurface carbon storage is relatively new, the process of storing injected fluids underground is not. Natural gas storage began more than a century ago to provide the capacity to meet winter heating needs. The widespread use of water injection wells began in the 1930s to dispose of oilfield brine and enhance oil recoveries.
The history of these operations provides insights into the types and frequency of failure incidents. Most are either facility-related failures that occur at the surface, or wellbore failures that allow fluids to migrate upwards to shallower reservoirs or the surface. In many cases, these projects are using wells that are decades-old, providing a sense of what could happen 40 or 50 years from now when carbon storage projects are reaching the end of their injection lives.
Geological factors are responsible for a small but significant fraction of injection project failures. These include 1) a lower than expected seal capacity of the overlying caprock, 2) the migration of injected fluids along fractures or across faults previously considered sealing, 3) an overestimate of the volume available for storage, 4) the migration of fluids away from the injector in an unanticipated direction, and 5) induced seismicity.
We will present several examples of these failures, illustrating what happened, the factors responsible, and how these could have been foreseen. We will then use these as a starting point to examine recent examples of carbon storage failures to gauge similarities and differences and recommend critical subsurface characterization and monitoring to minimize future carbon storage failures.
We will also compare these recommendations to regulatory requirements and provide a critical view of why adherence is necessary but may not be sufficient to ensure a project will proceed without incident. For example, subsurface models are likely to be much simpler than the reservoir itself creating the possibility that failure mechanisms may be missed. There is also inherent bias in conducting studies with the intent of demonstrating that carbon can be stored safely as opposed to determining whether safe storage is possible.
These studies, in turn, can lead to underestimates of uncertainty and risk, which need to be calibrated to failure rate data from analogous wells and existing subsurface projects to help ensure objective and accurate predictions regarding the chance of project failure.