Certification framework based on effective trapping for geologic carbon sequestration

Abstract

We have developed a certification framework (CF) for certifying the safety and effectiveness of geologic carbon sequestration (GCS) sites. Safety and effectiveness are achieved if CO 2 and displaced brine have no significant impact on humans, other living things, resources, or the environment. In the CF, we relate effective trapping to CO 2 leakage risk which takes into account both the impact and probability of leakage. We achieve simplicity in the CF by using (1) wells and faults as the potential leakage pathways, (2) compartments to represent environmental resources that may be impacted by leakage, (3) CO 2 fluxes and concentrations in the compartments as proxies for impact to vulnerable entities, (4) broad ranges of storage formation properties to generate a catalog of simulated plume movements, and (5) probabilities of intersection of the CO 2 plume with the conduits and compartments. We demonstrate the approach to a hypothetical GCS site in a Texas Gulf Coast saline formation. Through its generality and flexibility, the CF can contribute to the assessment of risk of CO 2 and brine leakage as part of the certification process for licensing and permitting of GCS sites around the world regardless of the specific regulations in place in any given country.3

Risk, Liability, and Economic Issues with Long-Term CO2 Storage—A Review

“…If there are no lateral seals in addition to this primary seal, the CO 2 can still migrate more or less horizontally along the underside of the caprock until it is trapped or finds a pathway to escape the storage reservoir (Szulczewski et al 2012;Birkholzer et al 2015). Geologic uncertainty concerning the pathways that injected CO 2 and pressurized or displaced formation fluids will take is a major contributor to uncertainty in estimates of potential risk (Oldenburg et al 2009;Pawar et al 2015).…”

“…According to , a hazard of leakage associated with GCS can be quantified as a probability of exceeding an acceptable volume or rate of leakage of CO 2 , brines, and/or total dissolved solids (TDS) out of the storage reservoir. Oldenburg et al (2009) define the probability of leakage as the product of the likelihood of the injected CO 2 (or displaced fluids) intersecting a conduit and the likelihood of that conduit intersecting a compartment that contains vulnerable receptors. Receptors could be on or near the surface, like the surface population, or located at various depths underground, like freshwater aquifers, deposits of hydrocarbon resources, or other natural resources.…”

“…Often, analysts estimate the impacts on intermediate receptors (such as increased concentration of TDS in a potable water aquifer) as proxies of the ultimate consequences for vulnerable entities within a compartment (such as humans exposed to contaminated water). In addition, there is no risk if there is no probability of eventual impacts on humans, other living things, the environment, water, or other essential natural resources (Oldenburg et al 2009). …”

“…Given the relatively benign properties of CO 2 , inflows of brines and other displaced storage formation fluids could have a greater impact on freshwater aquifers than the CO 2 . In this scenario, migration allows the CO 2 and brines to eventually intersect minor faults and fractures, but the probability of leakage to the surface via such potential conduits is extremely low (IEAGHG 2007b;Oldenburg et al 2009;Stenhouse et al 2009;Keating et al 2013;Pawar et al 2014Pawar et al , 2015Birkholzer et al 2015).…”

“…Even within the AoR for the storage project, there will be geologic uncertainty about potential subsurface pathways for migration of CO 2 and displaced fluids that may not be completely resolved through site characterization. Still, if leakage occurs onsite it is more likely to be detected and mitigated earlier than if it occurs further afield (IEAGHG 2007a(IEAGHG , b, 2012CSLF 2009CSLF , 2012Oldenburg et al 2009;Lu et al 2013;Pawar et al 2014Pawar et al , 2015.…”