Third EAGE Conference on Carbon Capture and Storage Potential

Monitoring strategies for offshore CCS cannot simply replicate those used in the oil and gas industry. Regulations mandate monitoring throughout the project’s entire lifespan, including decades post-closure. CCS calls for cost-effective solutions, making expensive high-resolution methods like seismic less viable. Moreover, environmental regulations pose challenges to the intensive use of seismic methods, that feature large CO2 footprints and active sources. Operationally, the presence of infrastructure like wind farms, hinders the systematic surveying patterns required for seismic monitoring. Last but not least, 4D seismic signal detectability can be low when CO2 is injected into depleted gas reservoirs due to the weak contrast with the preexisting residual gas. Time-lapse gravity and seafloor deformation monitoring is a mature commercial technology used for 25 years in Norway to fully replace or complement 4D seismic in gas-producing reservoirs. Recent modeling for CCS projects like Morecambe in the UK demonstrates very significant and robust time-lapse gravity signals after one year of injection, indicating an excellent capability to delineate both the CO2 and the pressure plumes. This offers a viable path forward for monitoring CO2 storage sites sustainably and cost-effectively, while overcoming the operational limitations of 4D seismic. This can be crucial for the long-term success and economic viability of CCS projects.

A typical reservoir for carbon capture and sequestration (CCS) consists of porous hydrous basalt formations with stiff and soft pores (cracks). Fe-and Ca-rich basalt formations are the most promising mafic reservoir where the dominant storage mechanism involves solubility and mineralization through water-rock-CO₂ reactions. Insights into the elasticity, porosity, and permeability of water-rock-CO₂ reactions have great potential for seismic monitoring in carbon sequestration, which remains largely unaddressed in the literature. Cements (carbonate nodules), growing around the edges of cracks/fractures, frequently block up fluid-flow pathways, significantly affecting permeability and consolidation. Based on double-porosity thermoelastic theory, we propose a thermo-chemo-mechanical model for water-rock-CO₂ reactions to estimate the carbon storage capacity of fractured reservoirs. Considering the permeability of soft cracks is affected by the radius of carbonate nodules, we estimate the P-wave velocity and the carbon amount sequestered after CO₂ injection.

Uncertainty in caprock assessment is one of the concerns in geologic carbon storage. It is especially caused in an area where an available geological dataset is lacking or limited. In such a case, a detailed database from a geological analogue can be utilized to reduce the uncertainty. This study investigated spatial changes in seal capacity of mudstones from onshore outcrops of the Pleistocene Kazusa Group near the Tokyo Bay area, to establish a geological analogue of caprock property in an active margin sedimentary basin. Seal capacity of the mudstones shows a distinct decrease landward in a relatively short distance from lower-slope to shelf-margin deposits, whares it is the highest and nearly constant in the basin-floor deposits. The findings can be utilized as a geological analogue for the caprock assessment in subsurface successions of this sedimentary basin as well as in other sedimentary basins with similar geological settings, such as high sedimentation rates and siliciclastic-dominated sedimentary successions formed in active margins.

For conformance monitoring (and, maybe, large leakage detection) in large-scale CO2 projects, it may be beneficial to use head waves refracted beneath the reservoir. We explore the feasibility of this approach through seismic modelling for a cartoon model of CarbonNet Pelican site. We also simulate a similar monitoring approach for a forthcoming shallow fault injection at the CO2CRC’s Otway site in the Australian State of Victoria. This experiment can be viewed as a scaled model for larger injections. Based on these modelling results, we provide a short overview of the further field experiments that can be used to validate the proposed approach.

Fiber-optic distributed acoustic sensing (DAS) technology is a technology that measures subsurface vibrations by probing the strain induced on a fiber-optic cable by an acoustic wavefield and has been demonstrated to provide a reliable alternative to traditional point receivers when deployed horizontally at surface (S-DAS). S-DAS, can record both P-wave (PP) and converted wave (PS) arrivals, is therefore well suited to monitoring CCS-related pressure and saturation changes when deployed in conjunction with a wider injection monitoring program. In recent years, we have demonstrated the significant potential of S-DAS imaging for both PP and PS wavefields. We report on our ability to image production-induced saturation changes and the potential to image production-based pressure changes, which provides valuable feedback in the early stages of the injection. We have demonstrated the key role S-DAS has to play as a low-cost seismic sensor, which can be interrogated over decades with no maintenance. Furthermore, through our novel acquisition geometry designs for S-DAS we also demonstrate its potential as a low impact, low acquisition footprint solution, lending itself to deployment in an adaptive manner, scaling the source effort to the phase of injection and monitoring objective; redefining the cost of seismic monitoring.

Understanding the migration of CO2 and water in complex geologic media is crucial for ensuring the safety and long-term efficacy of CO2 geological storage. Geologic heterogeneity has a significant effect on multiphase flow properties as well as CO2 trapping mechanisms. This study investigates CO2 migration and trapping mechanisms in heterogeneous geological media utilizing X-ray imaging technique. Both the core- and pore-scale multiphase flow experiments were conducted using a sandstone with sedimentary lamination. At the core scale, capillary heterogeneities influenced CO2 displacement, with higher initial saturations widening the residual trapping distribution. New flow regimes during dissolution were identified, and a scaling relationship for their temporal evolution was proposed. Pore-scale analysis revealed micro-scale heterogeneities impacting CO2 flow dynamics, with spatial variation in capillary entry pressure leading to non-uniform flow. In-situ imaging captured CO2 cluster breakup and local imbibition processes. These findings enhance our understanding of multiphase flow in heterogeneous porous media, and our study underscores the importance of considering both core- and pore-scale heterogeneities for CO2 geological storage.

During the initiation stages of CO2 storage projects, predicting the ultimate plume distribution presents a significant challenge due to the presence of substantial uncertainties in subsurface conditions. These uncertainties, when predicting plume distribution, need to be handled in a consistent way to better assess risks related to containment and to ultimately determine a storage site as having a low risk profile. This paper summarizes a method that utilizes ensemble-based approaches to create a range of realizations that represent uncertainty from the outset, to characterize uncertainties in static geomodels. A dynamic simulation is performed on each of these geomodel realizations using a modified invasion percolation simulator to improve model runtimes and deliver accurate representations of plume migration. The simulation outcomes are compared to known plume distributions to assess conceptual leakage risks. What we discovered was that even in a highly studied storage site with relatively low heterogeneity, our predictions remain highly sensitive to uncertainties. This underscores the need for robust assessment methods when evaluating new targets, regardless of how much we may think we already know.

Demonstration scale CO2 geological storage has been proposed in the lower Precipice Sandstone, Surat Basin, Australia. The Evergreen Formation is the overlying seal (cap-rock), and the Moolayember Formation of the Bowen Basin the underlying formation (bottom seal). CTSCo has drilled several wells for feasibility studies. The potential for CO2-water-rock reactions to release metals to low salinity groundwater was a potential risk since the site is within the Great Artesian Basin. Metals were hosted in several minerals in the West Wandoan 1 well rock cores, with total concentrations higher in the Moolayember Formation and reservoir mudstones, than in the reservoir sandstones. Drill cores were reacted with supercritical CO2 or impure CO2-SO2-NO-O2 at in situ conditions. Minerals including calcite, ankerite, siderite, Fe-rich chlorite, and sulphides reacted. Dissolved Ca, Mn, Zn, Rb, etc. were released at variable concentrations dependant on the rock mineral content and gas stream. Fe and Pb generally increased initially, then decreased as Fe-oxyhydroxide minerals precipitated especially in the presence of O2. Carbonates were the main sources of metals as they dissolved more readily, with some release from ion exchange/desorption. Ultimately, a reactive transport model built from the data predicted that water quality impacts were restricted to the CO2 plume.

A Measurement, Monitoring and Verification (MMV) plan is a requirement for subsurface CO2 sequestration projects. A complete MMV plan considers the reservoir location, depth, type, target disposal volume, and time requirement. It also considers the site characteristics, integrity of the storage complex, wells, and specific geologic features. Finally, it conforms to the local governing compliance regulations, guidelines, and mandates on MMV planning.

The MMV design process works within the risk management framework and starts after site selection by evaluating site-specific storage risks before proceeding to implement additional safeguards supported by monitoring in a stepwise approach. The full MMV plan development process evolves from the conceptual stage, through a feasibility stage, to a define stage and includes operations during pre-injection, injection, and site closure.

The risk-based plan is comprehensive to anticipate any unwanted CO2 migration and adaptive to change or expand monitoring as the CO2 storage is underway. The result is an explicit monitoring plan that demonstrates the achievement of objectives, supports strategic planning and field development, helps decision makers make informed choices, prioritize actions, and distinguish among alternative courses of action. The plan accounts for uncertainty, the nature of the uncertainty, and how it can be addressed.

Western Australia provides ideal conditions for establishing carbon capture, utilization and storage (CCUS) hubs due to the co-location of abundant, highly suitable geological storage resources in saline aquifers and depleted fields with clusters of industrial emissions sources. Emitters include sources with high CO2 concentrations from gas processing, ammonia and fertilizer production that form a low-cost opportunity for the initial stages of a CCUS hub.

For techno-economic analysis, two main emissions clusters were identified: a) the Perth-Kwinana industrial area in the southwest of Western Australia with approximately 20 Mtpa of CO2 emissions and b) the Pilbara area in the northwest with approximately 30 Mtpa of CO2 emissions. Emissions in the Perth-Kwinana area are associated largely with power generation and alumina processing, whereas LNG processing, fertilisers and iron ore processing are the main CO2 sources in the Pilbara region. Approximately 5 Mtpa are reservoir CO2 separated from natural gas processing and high-CO2 streams from ammonia/fertiliser production and present a low-cost opportunity for the initial stages of a CCUS hub. The remaining 45 Mt of these emissions are associated with higher capture costs. Geological storage of CO2 is proposed in the offshore North Carnarvon Basin, which is a mature petroleum province.