Evaluation of Practicable Subsurface CO2 Storage Capacity and Potential CO2 Transportation Networks, Onshore North America

Abstract

Carbon Capture, Utilization and Storage (CCUS) is considered to be a potentially important technology for reducing the amount of carbon dioxide (CO2) released into the atmosphere from anthropogenic emission sources. With recent progress on capture technologies, attention is increasingly turning to the identification of key challenges associated with CO2 transportation and storage at the scale being considered for the CCUS industry. Decades of oil and gas production have provided experience in application of technologies required for CO2 transportation and storage, but the challenges unique to CO2 storage still need to be evaluated. This paper describes a scoping-level assessment of practicable subsurface geologic CO2 storage capacity and a potential Carbon Capture, Utilization, and Storage (CCUS) industry in the US and Canada, leveraging publically available data/information, publications, and methodologies. Likely subsurface CO2 storage sites and distribution of storage capacity relative to major anthropogenic sources are first characterized using a probabilistic methodology previously developed by the US Geologic Survey (USGS), which was modified to account for several practical factors affecting storage capacity. Major factors considered include 1) subsurface lateral accessibility restrictions imposed by faulting and/or stratigraphic pinch-outs, 2) the proportion of net storage-quality sand comprised of thin sands unlikely to be good injection candidates, 3) surface access restrictions, and 4) dynamic injectivity/storage efficiency considerations. Potential regional CCUS networks are then modeled using a transportation cost framework to map CO2 sources to storage sinks. The USGS assessment and most other existing assessments of storage capacity are based on the premise that all engineering approaches and hardware required to achieve the highest possible storage efficiency would be employed, and that injection rate and timeframe are not issues, with perhaps hundreds to thousands of years of injection permitted to achieve full storage efficiency. We explore the impact of dynamic injectivity considerations on practical storage efficiency by using reservoir simulation models to account for subsurface pressure limitations and the impact of permeability differences and lateral accessibility on CO2 injectability, and then use the results of the modeling to derive a debiting function that reduces the range of static storage capacity estimated by the USGS. Debiting functions accounting for lateral accessibility, thin sands, and surface access restrictions were also applied to obtain practicable storage estimates. Key conclusions from the study include: 1) Although the modified storage capacity estimates are lower than previously published estimates, the estimated subsurface storage capacity in the US onshore is sufficient to sustain a large-scale CO2 storage industry. We estimate that about 500 Gt of potential US subsurface storage capacity is potentially available (excluding federal offshore capacity) even after accounting for dynamic injectibility considerations, thin sands, surface and lateral access issues. Dynamic injectability factors had the largest impact on the reduction in estimated storage capacity. 2) Significant geographic misalignment exists between current high-volume CO2 emission sources and storage availability in North America. This could affect evolution of CO2 transportation networks with time. Detailed site-specific assessments of subsurface storage capacity are required for site selection and actual project implementation. These efforts could change some of the conclusions of this study. In particular, consideration of legacy wells and geomechanical factors such as induced seismicity, ground surface deformation, and fault activation may further reduce storage capacity relative to the estimates presented here. Nevertheless, the methodology described in this paper may be useful for initial assessment of CO2 storage capacity and matching of CO2 emission sources to storage sinks in geographic locations other than those considered in this study.