CCUS

 

Carbon Capture, Utilization and Storage

Contact PEM for evaluation of portable ¹⁴CO₂ analyzer applications to identify and quantify CCUS leakage here.

MVA Background

Monitoring, verification and accounting (MVA)

MVA has been identified as one of the most important ways to ensure that carbon capture and storage (CCS) and carbon capture, utilization and storage (CCUS) projects are cost-effective in avoidance of CO₂ to the atmosphere, offer reliable storage permanence of > 99% and are safe to humans and the ecosystems they rely upon (e.g., Hicks et al. 2015). Leakage associated with injection pressure and injection wells, inappropriately sealed abandoned wells, or unidentified/poorly characterized faults, caprock and leakage through permeable pathways (e.g., Benson et al. 2009).  and fractures may result in point, line, or area CO₂ sources of varying intensity.  Reliable monitoring systems, with the required sensitivity and resolution, must therefore be available for a range of leakage scenarios. Detection and characterization of potential CO₂ leakage from CCS sites may be challenging in the near-surface environment due to the large spatial and temporal variation in background CO₂ fluxes (e.g., Oldenburg et al. 2003; Lewicki 2005; Leuning et al. 2008). Also, the area of a given surface CO₂ leakage signal could be several orders of magnitude less than the total area (e.g., ~100 km²) of the CO₂ reservoir above which monitoring will be carried out (e.g., Lewicki & Hilley 2009) . Consequently, innovative and advanced monitoring technologies are required with the capability to detect, locate, and quantify CO₂ leakage signals with potentially small magnitude and area, relative to background CO₂ variations and the total area of investigation, respectively (e.g., Lewicki et al. 2012; Nickerson & Risk 2013; Risk et al. 2015).

While measurements of CO₂ concentrations in groundwater, soil gas, and the atmosphere and surface CO₂ fluxes have important and complementary roles to play in CCS monitoring programs, leakage of fossil fuel-derived CO₂ (ff-CO₂) from CCS sites cannot be deduced directly from these measurements because they cannot distinguish it from CO₂ released from other background sources (e.g., terrestrial ecosystems, other ff-CO₂ sources). Additional measurements are therefore needed to identify and quantify ff-CO₂ concentrations and fluxes. Introduced and natural tracers may provide the ability to trace the movement of CO₂ in the subsurface and atmosphere and identify its source. CO₂-soluble tracers such as SF₆, pure ¹⁴CO₂ and perfluorocarbons can be introduced into the CO₂ injection stream (e.g., Cheng et al. 2007; Bachelor et al. 2008; Zhong et al. 2014; Amonette et al. 2014).  However, many of these tracers have very high greenhouse warming potential, pose inherent hazards of handling and are infeasible considering the high cost of frequent sampling and analysis by traditional accelerator mass spectrometry (AMS) discussed in detail below.   While measurements of the natural tracer ¹³CO₂ are accurate, low-cost, and provide information on biogenic sources of CO₂, they will not be sensitive geochemical tracers of ff-CO₂ because of the similarities in isotopic signatures of ff-CO₂ and terrestrial ecosystems. Specifically, ¹³CO₂ will not provide discrimination between magmatic CO₂ and ff-CO₂ in areas where mixtures of such gases may occur (e.g., abandoned oil and gas wells). The doping of injection sites with highly enriched ¹⁴CO₂ can amplify the leakage signal (e.g., Bachelor et al. 2008) however, the handling of enriched radiocarbon comes at a price for regulatory compliance for handling and accounting of radiocarbon as well as the possibility of exposure to humans above recommended dosage rates and the possible contamination of the surrounding environment (e.g., Seto & McRae 2011). Figures A and B summarize the sampling methods and areas within the Quest CCS site proposed in this work.

Status of Current ¹⁴CO₂ Analyzers. To-date, there are no commercial high precision field-ready ¹⁴CO₂ analyzers available to the best of our knowledge. Accelerator mass spectrometry (AMS) is the preferred method for analysis of ¹⁴CO₂ providing the highest precision results attainable, in many cases with a precision of ≤ 2 per mil  (‰) but more typically 2-7 ‰ based on AMS intercalibration data (e.g., Miller 2013). The cost of AMS is considerable for a single sample (~$600 to $1,000) and cannot be analyzed in real-time relative to the needs of a CCS monitoring program employing continuous well-known CCS sampling methods such as eddy covariance (e.g., Lewicki et al. 2012; Moni & Rasse 2014; Moreira et al. 2014; Jenkins et al. 2016; Sun et al. 2016) and soil accumulation chambers (e.g., Leuning et al. 2008; Elío et al. 2014). The AMS analysis of discrete flask samples from a CCS site has been demonstrated and while recognizing ¹⁴CO₂ as the best method for leakage detection researchers defer to alternative methods due to the infeasibility and high cost of flask collection and handling for AMS analysis (Nickerson & Risk 2013; Risk et al. 2013; Risk et al. 2015). As full-scale CCS facilities increase and underlying CO₂ geologic reservoirs expand, surveillance sampling over large areas (e.g., 10-100 km²) will present the need for increasingly higher numbers of flask samples compounding the infeasibility and cost of AMS.  In addition, the use of flasks to capture samples for isotopic analysis combined with dynamic measurements of CO₂, in lieu of a continuous flow ¹³CO₂ analyzer, have proven inconclusive. For example, relaxed eddy covariance, a method in which eddy covariance measurements are paired with concurrent gas collection in tedlar bags for isotopic analysis, have not been validated (e.g.,Bowling et al. 1998) or have shown that the integration time of > 4 minutes did not capture the desired fast isotopic exchange between carbon reservoirs (e.g., Griffis et al. 2008). Wher et al. (2013) employed a continuous flow analyzer (4 Hz) with a 100 second integration time for direct measurements of ¹³CO₂ (e.g, Nelson et al. 2008) representing the isotopic composition of net ecosystem-atmosphere exchange (NNE) over the growing season of a temperate deciduous forest. The results of Wehr et al. (2013) suggest that a 100 second integration time was sufficient for the elucidation of eddy-induced isotopic fluctuations for ecosystem-scale carbon balance. A comparison of flask data with that for continuous flow ¹³C eddy covariance again illustrated the mismatch of the flasks slow response function with that of fast response of eddy covariance (e.g., Wehr et al. 2013). Currently, there are three commercially available fast response analyzers suitable for eddy covariance for  ¹³CO₂, ¹³C¹⁶O¹⁷O and ¹³C¹⁶O¹⁸O, one of which will be selected as a component of the revised GMP platform described below. The combination of ^{12, 13,1 4}CO₂ NEE isoflux has not been demonstrated to our knowledge but is the most direct and powerful means to differentiate ecosystem function from surface and near-surface signal detection of CCS ff-CO₂.