A Hierarchical Framework for CO2 Storage Capacity in Deep Saline Aquifer Formations

Carbon dioxide (CO2) storage in deep saline aquifers is a vital option for CO2 mitigation at a large scale. Determining storage capacity is one of the crucial steps toward large-scale deployment of CO2 storage. Results of capacity assessments tend toward a consensus that sufficient resources are available in saline aquifers in many parts of the world. However, current CO2 capacity assessments involve significant inconsistencies and uncertainties caused by various technical assumptions, storage mechanisms considered, algorithms, and data types and resolutions. Furthermore, other constraint factors (such as techno-economic features, site suitability, risk, regulation, social-economic situation, and policies) significantly affect the storage capacity assessment results. Consequently, a consensus capacity classification system and assessment method should be capable of classifying the capacity type or even more related uncertainties. We present a hierarchical framework of CO2 capacity to define the capacity types based on the various factors, algorithms, and datasets. Finally, a review of onshore CO2 aquifer storage capacity assessments in China is presented as examples to illustrate the feasibility of the proposed hierarchical framework.

Filling and drainage of a subglacial lake beneath the Flade Isblink ice cap, northeast Greenland

The generation, transport, storage and drainage of meltwater beneath the ice sheet play important roles in the Greenland ice sheet (GrIS) system. Active subglacial lakes, common features in Antarctica, have recently been detected beneath GrIS and may impact ice sheet hydrology. Despite their potential importance, few repeat subglacial lake filling and drainage events have been identified under Greenland Ice Sheet. Here we examine the surface elevation change of a collapse basin at the Flade Isblink ice cap, northeast Greenland, which formed due to sudden subglacial lake drainage in 2011. We estimate the subglacial lake volume evolution using multi-temporal ArcticDEM data and ICESat-2 altimetry data acquired between 2012 and 2021. Our long-term observations show that the subglacial lake was continuously filled by surface meltwater, with basin surface rising by up to 55 m during 2012–2021 and we estimate 138.2 × 106 m3 of meltwater was transported into the subglacial lake between 2012 and 2017. A second rapid drainage event occurred in late August 2019, which induced an abrupt ice dynamic response. Comparison between the two drainage events shows that the 2019 drainage released much less water than the 2011 event. We conclude that multiple factors, e.g., the volume of water stored in the subglacial lake and bedrock relief, regulate the episodic filling and drainage of the lake. By comparing the surface meltwater production and the subglacial lake volume change, we find only ~64 % of the surface meltwater successfully descended to the bed, suggesting potential processes such as meltwater refreezing and firn aquifer storage, need to be further quantified.

Aquifer Storage and Recovery Feasibility Study With Flowing Fluid Electrical Conductivity Logging in Shallow Aquifers of South Bihar, India

Growing dependence on groundwater to fulfill the water demands has led to continuous depletion of groundwater levels and, consequently, poses the maintenance of optimum groundwater and management challenge. The region of South Bihar faces regular drought and flood situations, and due to the excessive pumping, the groundwater resources are declining. Rainwater harvesting has been recommended for the region; however, there are no hydrogeological studies concerning groundwater recharge. Aquifer storage and recovery (ASR) is a managed aquifer recharge technique to store excess water in the aquifer through borewells to meet the high-water demand in the dry season. Therefore, this paper presents the hydrogeological feasibility for possible ASR installations in shallow aquifers of South Bihar with the help of flowing fluid electrical conductivity (FFEC) logging. For modeling, the well logging data of two shallow borewells (16- and 47-m depth) at Rajgir, Nalanda, were used to obtain the transmissivity and thickness of the aquifers. The estimated transmissivities were 804 m2/day with an aquifer thickness of 5 m (in between 11 and 16 m) at Ajatshatru Residential Hall (ARH) well. They were 353 and 1,154 m2/day with the aquifer thicknesses of 6 m (in between 16 and 22 m) and 2 m (in between 45 and 47 m), respectively, at Nalanda University Campus (NUC) well. Despite the acceptable transmissivities at these sites, those aquifers may not be fruitful for the medium- to large-scale (more than 100-m3/day injection rate) ASR as the thickness of the aquifers is relatively small and may not efficiently store and withdraw a large amount of water. However, these aquifers can be adequate for small (up to 20-m3/day injection rate) ASR, for example, groundwater recharge using rooftop water. For medium- to large-scale ASR, deeper aquifers need to be further explored on these sites or aquifers with similar characteristics.

ASCAPE: A Flexible and Efficient Analytical Tool to Evaluate Aquifer Storage Capacity for CO2 Sequestration

In recent years, carbon neutrality has emerged as an important social and political focus globally, where carbon sequestration plays a key role. The present work is aimed at introducing ASCAPE (Aquifer Storage CAPacity Evaluation tool), a fast and flexible tool useful in case of CO2 aquifer sequestration to preliminarily evaluate the required storage capacity as a function of the maximum allowable pressure increment. ASCAPE is based on the volumetric method included in SPE "Guidelines for Applications of the CO2 Storage Resources Management System" (SPE, 2020) for aquifer sequestration. The analytical formula was integrated to include additional physical phenomena as CO2 solubility in water, pressure control through water production, effect of gas pools connected to aquifer. The tool, implemented in Excel/VBA environment, allows to easily obtain a theoretical Pressure increment vs. Aquifer Volume curve useful to estimate the required aquifer volume to store a given quantity of CO2. ASCAPE results were validated comparing to a simplified 3D model simulated by a compositional commercial dynamic simulator. The validation showed a very good alignment with the 3D dynamic simulation results under several conditions. Many tests were performed with and without the CO2 solubility model, demonstrating that this phenomenon acts as pressure increment reducer. The original volumetric model can be therefore considered slightly conservative, since it neglects this physical contribution, which allowed to improve the reliability of the proposed analytical model. The proposed methodology is a general-purpose application being not related to a specified candidate and, therefore, it can be tailored on the specific scenario to be evaluated. ASCAPE was developed for preliminary screening of CO2 sequestration concepts in greenfield development areas, where the absence of brown or exhausted fields makes the storage in aquifer the only viable solution. Different aquifers were compared under certain assumptions of carbon to be stored with and without water production, allowing a preliminary evaluation that will be used to rank the concepts in terms of technical/economic feasibility.

Hydrologic changes of in-situ gravimetry

Inter-seasonal and geodynamics-related gravity changes are important geoscientific signals that are extractable from gravimeter observations after deducing background information as local hydrology gravity effect. With two superconducting gravimeters (SGs, OSG-053 and iGrav-007) located in different tectonic units, continuous Global Navigation Satellite System data, and AG observations, Wuhan (China) is an ideal location for investigating the effects of gravity resulting from significant local hydrology mass variations. We processed ∼26 months of gravity data collected from the SGs in Wuhan and obtain residuals of -40 nm.s2 for OSG-053 and 100 for iGrav-007. The hydrological observations show an estimated gravity increase of 42 nm.s2 near iGrav-007, which mainly resulted from the increased unconfined water level with an aquifer-specific yield of approximately 0.1. However, the gravity changes around OSG-053 are mainly from soil moisture and reach -90 nm.s2. The soil type, thickness and water content parameters were obtained from hydrogeological survey and drilling data. The deep confined water level rose by 2.5 m, which introduced a 1 nm.s2 gravity variation with a specific storage about 0.00001 from field unsteady flow pumping test. The modeled gravity is approximately -40 nm.s2 around OSG-053 and 90 around iGrav-007, in accordance with the observed gravity variations. The difference in gravity changes between the two SG observations can be explained by different local water storage environments. Our results suggest that unconfined and soil water significantly impact the in-situ gravimetry, which indicates that further detailed hydrogeological surveys are required. A combined investigation of gravity and water levels can be a useful approach to monitor aquifer storage conditions and groundwater management.

Linkages between GRACE water storage, hydrologic extremes, and climate teleconnections in major African aquifers

Water resources management is a critical issue in Africa where many regions are subjected to sequential droughts and floods. The objective of our work was to assess spatiotemporal variability in water storage and related controls (climate, human intervention) in major African aquifers and consider approaches toward more sustainable development. Different approaches were used to track water storage, including GRACE/GRACE Follow On satellites for Total Water Storage (TWS); satellite altimetry for reservoir storage, MODIS satellites for vegetation indices, and limited ground-based monitoring. Results show that declining trends in TWS (60–73 km3 over the 18 yr GRACE record) were restricted to aquifers in northern Africa, controlled primarily by irrigation water use in the Nubian and NW Saharan aquifers. Rising TWS trends were found in aquifers in western Africa (23–49 km3), attributed to increased recharge from land use change and cropland expansion. Interannual variability dominated TWS variability in eastern and southern Africa, controlled primarily by climate extremes. Climate teleconnections, particularly El Nino Southern Oscillation and Indian Ocean Dipole, strongly controlled droughts and floods in eastern and southern Africa. Huge aquifer storage in northern Africa suggests that the recent decadal storage declines should not impact the regional aquifers but may affect local conditions. Increasing groundwater levels in western Africa will need to be managed because of locally rising groundwater flooding. More climate-resilient water management can be accomplished in eastern and southern Africa by storing water from wet to dry climate cycles. Accessing the natural water storage provided by aquifers in Africa is the obvious way to manage the variability between droughts and floods.

Aquifer Susceptibility to Groundwater Pumping in Kediri City, East Java Province, Indonesia

The development of Kediri City in various sectors, such as industry, agriculture, and population growth, also increases water. The utilization of groundwater is still a major mainstay in this area. The utilization of groundwater includes the construction of production wells for irrigation and raw water. The aquifer susceptibility should be considered during groundwater exploitation to minimize a negative impact on the environment. This research aims to analyze the susceptibility of the aquifer to pumping in Kediri City, which is helpful for planning and making decisions in the management of groundwater resources. The determination of aquifer susceptibility is based on aquifer response characteristics, aquifer storage characteristics, allowable subsidence of groundwater level, and depth to the groundwater table. Based on those parameters, it can be concluded that the aquifer susceptibility on groundwater utilization in Kediri City is at moderate and high levels. Areas with moderate aquifer susceptibility are located on the west side of Kediri City, and high aquifer susceptibility is in the middle to the eastern side of Kediri City.

Mapping Aquifer Storage Properties Using S-Wave Velocity and InSAR-Derived Surface Displacement in the Kumamoto Area, Southwest Japan

We present a novel approach to mapping the storage coefficient (Sk) from InSAR-derived surface deformation and S-wave velocity (Vs). We first constructed a 3D Vs model in the Kumamoto area, southwest Japan, by applying 3D empirical Bayesian kriging to the 1D Vs profiles estimated by the surface-wave analysis at 676 measured points. We also used the time series of InSAR deformation and groundwater-level data at 13 well sites covering April 2016 and December 2018 and estimated the Sk of the confined aquifer. The Sk estimated from InSAR, and well data ranged from ~0.03 to 2 × 10−3, with an average of 7.23 × 10−3, values typical for semi-confined and confined conditions. We found a clear relationship between the Sk and Vs at well locations, indicating that the compressibility of an aquifer is related to the stiffness or Vs. By applying the relationship to the 3D Vs model, we succeeded in mapping the Sk in an extensive area. Furthermore, the estimated Sk distribution correlates well with the hydrogeological setting: semi-confined conditions are predicted in the Kumamoto alluvial plain with a high Sk. Our approach is thus effective for estimating aquifer storage properties from Vs, even where limited groundwater-level data are available. Furthermore, we can estimate groundwater-level variation from the geodetic data.

Borehole siting and construction in rural Malawi: A sociotechnical process?

Choosing the site for a new water well in rural southern Malawi is essentially a political process with competing priorities and stakeholders. For a new well (or borehole) to be sustainably used and maintained, the relevant stakeholders must be fully engaged in the siting process and given meaningful responsibility for the final siting decision. However, without sound technical information, a siting decision based solely on stakeholder priorities such as proximity to the headman’s compound or accessibility to the center of population, may not result in a satisfactory borehole. Instead, in addition to stakeholder interests, we used a process that includes electrical resistivity tomography (ERT) as a tool to guide and constrain the local decision-making process. Within the region of the crystalline-basement aquifer, ERT profiles indicate variations in weathering thickness, hence aquifer storage. In a lacustrine setting, the ERT profile delineated a zone of moderately large resistivity associated with a deposit of fresh-water saturated sand. This ERT-derived technical information becomes one element in a comprehensive sociotechnical approach to the location of sustainable water resources. We used this sociotechnical approach to complete boreholes for all four villages in our project and have a high confidence that the villagers will be motivated to use and maintain these resources.