The Fourth EAGE Global Energy Transition Conference and Exhibition

Carbon capture and storage (CCS) has become an increasingly important technology for mitigating the effects of climate change. One of the key challenges is the need for reliable monitoring to ensure safe CO2 storage. Time-lapse seismic is a commonly used and very effective tool due to the strong velocity contrast between brine and supercritical CO2 filled pore space, which allows for CO2 plume migration monitoring ( Furre et al., 2016 ). CO2 saturation monitoring during and after injection is also crucial, but time-lapse seismic becomes less effective with increasing saturation due to the less pronounced velocity change. Time-lapse gravity ( Furre et al., 2016 ) has emerged as a suitable method for providing this additional information given the linear relationship between saturation and density. We show a straightforward method that can be used to quickly screen for the suitability of gravity monitoring for possible CO2 storage sites. Instead of detailed modelling, the method is grounded in analytical calculations which were implemented in a lean tool. Necessary simplifications due to the analytical method make results for various reservoirs comparable and sensitivities can be better understood. However, more detailed studies need to follow if the screening results for a CO2 storage site are encouraging.

The Greensand project aims to develop Paleogene sands in the Siri Canyon offshore Denmark for safe long-term CO2 storage with the initial focus on the Nini West depleted oil field. The seal consists of a primary caprock succession of marine shales from the Horda to mid Lark formations and a secondary caprock succession from the mid to upper Lark formation, totalling approximately 900 meters in thickness including sandy siltstone beds in the secondary seal. The applied work stream extensively examines the geological seal parameters using a multidisciplinary framework. This includes determining elemental composition, mineralogy, grain size distribution, porosity, permeability, specific surface area, pore throat size distribution, and capillary entry pressure data from core and cuttings samples in the Nini area. Digital rock analysis was conducted on cuttings representing sandy siltstone beds within the secondary seal. A petrophysical workflow is described, incorporating algorithms for calculating grain size fractions, total porosity, grain density, specific surface area, and permeability utilizing wireline logs based on analytical data. Highest seal capacity was found in the smectite rich primary seal compared to the illite-kaolinite dominated secondary seal. The study documents that the seal exhibits a high capacity for withholding CO2 in the subsurface.

The selection criterion for future underground hydrogen storage may initially be based upon the storage capacity combined with the proximity to the hydrogen transport network. This market driven approach neglects other information which may strongly influence the economics of such storage. Several risks such as legacy or abandoned wells, cap rock quality or microbial activity might alter the development of the underground storage. The Analytical Hierarchy Process was applied to identify the most suitable storage opportunity between salt caverns and porous media traps (covering depleted fields, existing underground gas storages and aquifers). Seven criteria were used in the analysis: the lithology of the seal, its estimated minimum thickness and lithology, the existing faults and number of abandoned wells, the lithology of the storage and its readiness level (estimated time to market), and the microbial risk. Following this analysis, when suitable salt deposits are available in a country, salt caverns are likely to be the most suitable setting for underground hydrogen storage. Porous media storages such as depleted gas fields or conversion of existing natural gas storages may also be suitable opportunities for underground hydrogen storage.

Hydrogen (H₂) has the potential to be a clean fuel alternative to replace hydrocarbons in a low-carbon economy. Since H₂ generation from renewable sources is intermittent, large storage sites will be needed to meet its demand. Salt caverns are excellent options for storing H₂ on a large scale because they have a large storage capacity and flexible operation with large injection and withdrawal rates. This study collects and analyzes a comprehensive database of 569 salt domes located in Texas, Louisiana, Mississippi, and the Gulf of Mexico. We assess the potential for H₂ storage on 98 onshore salt domes without pre-existing caverns and suitable depth range for three scenarios (low, base, and high cases). For the base scenario, we estimate that these salt domes can accommodate a total of 2,550 caverns, with a potential working gas volume for H₂ of 4.59 trillion standard cubic feet (Tscf), and an energy storage potential of 368 terawatt-hours (TWh). This study also provides a breakdown of these results by state, county, and salt dome.

This study is the first of its kind, offering comprehensive information about salt domes in Texas, Louisiana, and Mississippi, along with an evaluation of their technical potential for H₂ storage.

The safety of CO2 storage operations requires the implementation of suitable monitoring techniques to evaluate conformance and containment of the storage process. The present research focuses on the NL (Northern Lights) case study (offshore Norway), aiming to assess the advantages of utilizing fiber optics in comparison to an array of land-based sensors (HNAR: HolsNoy Array and NNSN: Norwegian National Seismic Network). The investigation revealed that fiber optic cables demonstrate promising capabilities for seismic monitoring. The experiment demonstrated the sensitivity of standard telecommunications fiber optic cables deployed at the seabed for passive seismic (DAS) monitoring systems. The fiber optic system successfully detected earthquakes with magnitudes between 0.5 and 2.2 up to 200 km from the cable, and 10 times more earthquakes than onshore sensors during a period exceeding one month, showcasing its robustness in seismicity detection. Signal processing techniques, including denoising procedures, were found to be crucial for enhancing the signal-to-noise ratio and accurately detecting small seismic events. Furthermore, the fiber optic cables enabled superior earthquake location accuracy when compared to onshore sensor arrays alone.

Among subsurface hydrogen storage methods, caverns formed by solution mining in salt formations have proven effective due to salt’s self-healing behavior and lack of chemical reactivity. The Delaware Basin, with its extensive bedded salt formations, offers opportunities for hydrogen storage. This case study used well data with Gamma Ray, Density, and Sonic log curves to identify and characterize the Castile and Salado Formations. Gamma Ray curves helped identify formation boundaries, and Density and Sonic logs differentiated halite- and anhydrite-rich members within the two formations. Halite-to-bulk salt thickness ratios were calculated to pinpoint significant halite accumulations. The study identified thicker salt deposits in specific regions, particularly in Lea County, Southern New Mexico, and Loving and Winkler Counties in Texas. The Castile Formation showed more predictability when using well-logs in the identification of cycles of halite and anhydrite, while the Salado Formation’s posed predictability challenges when trying to halite heterogeneity. The research provides insights and a petrophysical workflow applicable to other salt-bearing basins for assessing hydrogen storage potential.

Ultra-High Resolution seismic images are more and more commonly used before installing an offshore wind turbine. The small sampling recorded by the dedicated acquisitions enables to image the subsurface with a resolution lower than 1 meter. To fully appreciate this resolution, comprehensive data processing and imaging must be applied, compensating for sea state variation and possible navigation uncertainties. Removing the ghost energy and stabilizing the emitted wavelet are crucial steps to retrieve the full resolution of the data, increasing bandwidth on both low and high frequency sides. The limited recorded information in the low frequency, below 100Hz, can be recovered through velocity model building, enabling further acoustic and possibly elastic inversion.

How can offshore wastewater be transformed into a critical energy transition resource?

The utilization of subsurface reservoirs for oil extraction, with subsequent utilization in CO2 sequestration and potential hydrogen storage, leads to the generation of significant quantities of produced water (PW) – 30 billion m3/year from Danish offshore production alone. Often exceeding oil extraction volumes, this PW is the primary waste from oil production, often discharged into the water column from most offshore platforms. Our research has delved into this issue and has successfully demonstrated the feasibility of extracting lithium from produced water. This discovery offers a twofold solution: it provides an avenue for re-injecting produced water, thereby reducing discharged PW while simultaneously reducing the discharge of metals into the sea. The simplicity of lithium carbonate extraction, even on offshore platforms, underscores its practicality. This achievement holds global significance, addressing critical raw material (CRMs) demands and aligning Danish offshore production with the European Union’s carbon neutrality goals. Our findings present an eco-friendly approach to resource management that contributes to a greener future while setting a model for responsible industry practices.

Within frame of the PilotSTRATEGY project, comprehensive geological characterization studies were conducted in the Lusitanian Basin to assess the CO2 storage potential in this Portuguese region. In the offshore area of this sedimentary basin, three promising geological structures were identified. Relying on well and geophysical data, each of them has been characterized to define their structural closure scenarios, reservoir petrophysical properties and dimensions as potential CO2 storage sites.

The current work presents a volumetric stochastic approach used to assess and integrate reservoir geological uncertainties for determining the CO2 storage capacities of the three identified structures. Following the volumetric estimation, a preliminary long-term storage capacity assessment was conducted for the most promising prospect Q4-TV1. The goal was to consider supplementary physical trapping mechanisms, such as mineral and solubility trapping, and to evaluate their impacts on storage capacity and CO2 plume dispersion over time.

By combining both storage capacity assessments, this work provides valuable insights and confirms the outstanding potential of prospect Q4-TV1 as a CO2 pilot injection site. Furthermore, this study highlights the feasibility of upscaling this prospect to a commercial-scale, contributing to the development of a viable carbon sink in the Lusitanian Basin.

With increased focus on green energy upscaling and diversification, geothermal energy is expected to play an increasingly significant role in the sustainable energy mix. As an energy source that is available virtually everywhere, geothermal resources can be used for power and heat for a range of applications. Additionally geothermal fluids can host high-demand elements, such as lithium, required for energy transition technologies.

As part of Global Geothermal Resource Assessment and Global Lithium Brines projects, we collated, integrated, and analysed numerous publicly available datasets for geothermal exploration insights, including temperature, fluid chemistry and production data.

An extensive amount of data is available for geothermal exploration and development. Integrating disparate datasets through robust data transformation and quality control processes allows us to construct comprehensive databases for analysis. Leveraging data-driven approaches on properly formatted data can provide valuable insights, validate models, and explain relationships and phenomena that may otherwise be poorly understood, for example when investigating temperature at depth in different areas, or predicting fluid properties.

However, collating and using diverse datasets comes with inherent challenges concerning discoverability, accessibility, and transformation. Understanding and addressing these challenges, and establishing best practices for data-handling, can unlock the value of public data for geothermal developments.