CO2 - H2 Optimisation in Rocks for Underground Storage (CHORUS)

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Geosciences


The UK is poised to embrace net zero carbon emission technologies to meet its Paris agreement targets, including offshore gas storage associated with the hydrogen (H2) fuel economy and Carbon Capture Usage and Storage (CCUS) schemes. Underground H2 storage (UHS) implies cyclic injection/depletion activities to deal with seasonal fluctuations associated with energy demands. For the cycle to be successful, a cushion gas is needed to keep the reservoir pressurised, with carbon dioxide (CO2) being a promising environmentally friendly alternative.
In most storage projects, reservoir fluids are seismically monitored by associating the variation of seismic amplitude with fluid content. However, if H2 is injected in CO2-cushioned reservoir, several factors obscure the H2 seismic visibility: both H2 and CO2 have similar acoustic properties, and they have short timescales to settle within an injection/extraction cycle, often imbibing the rock in patches and lowering effective fluid mobility.
In CHORUS we propose to address these issues by testing the hypothesis that a viscosity contrast is the key to seismic H2 detectability. We propose to test this hypothesis in three stages using our current expertise with dispersive wave propagation. First, we will perform ultrasonic laboratory measurements of elastic properties of reservoir rocks saturated with fluids expected to be found in UHS applications. Second, we will apply existing rock physics models established for CCUS to calculate the seismic velocities, attenuation and dispersion of reservoir rocks under different saturation conditions involving reservoir rocks saturated with H2-water and CO2-water below a caprock seal and calibrate these models using laboratory measurements. Third, we will identify how these finds scale up by calculating synthetic seismic data corresponding to a vertical seismic profile time-lapse experiment. Using this synthetic dataset, we will conduct a sensitivity analysis in order to understand the limits of seismic detectability of H2.
Outcomes of this proposal have the potential to be used to de-risk the injection process by enhancing our ability to quantify H2 through better seismic resolution of the H2-CO2 interface. They can be used to inform policy-makers by identifying proxies for leakage risk and facilitate the planning of injection and monitoring strategies for industrial seasonal UHS. The methodology can be further used to asses caprock integrity by incorporating geomechanical effects from fracturing on the synthetic seismic signatures, a direction that we intend to explore in further research.
We propose to disseminate our results in the form of two (six monthly) reports, a collaborative scientific publication in a lead academic journal, a collaborative conference publication and openly accessible data from the rock physics experiment and the synthetic seismic experiment. Using this project as springboard proof-of-concept, we intend to consolidate its finds by pursuing a long-term UK collaboration through a NERC Pushing Frontiers funding proposal. Such a proposal would incorporate fundamental research, as well as detailed anisotropic modelling of fractured top-seal/reservoir and seismic data. In addition, our theoretical advancements can add value to ongoing studies associated with UHS, both in NOC (NERC MOET), and UoE (EPSRC HyStorPore) by complementing them with rock physical knowledge.


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