Eni's portfolio in the UK contains several late-life assets with potential suitability for Carbon Capture and the Liverpool Bay Area Carbon Capture and Storage (LBA CCS) project aims at developing a decarbonisation hub on the North-western coast of England and Wales. Three depleted fields have been identified and selected as storage sites. A full workflow has been developed, starting from the 3D-reservoir simulation models, coupled to assess the plume evolution within the base case scenario storage (lasting for 25 years). The results provide the basis for the Flow Assurance studies to determine fluid behaviour within the injection string and support the equipment design. Based on the reservoir simulation outcomes, Cap Rock integrity study and Thermal Induced Fracture occurrence have been studied, showing no major limitation for both the reservoir sandstone and the associated over-burdens. Geochemical simulations, accounting forwater vaporization and CO2-brine-rock interactions, show limited reactivity with a negligible impact on near wellbore petrophysics (e.g. porosity) thus preserving the injectivity.
CCS projects have stepped onto the stage in the last decades as one of the most promising technique to contain CO2 atmospheric emission. The selection of storage candidates has looked for deep saline formation (i.e. aquifer) to secure the storage of high quantities of carbon dioxide due to their large storage capacities (Sleipner). Nevertheless, depleted gas reservoirs have the potential to become a much more viable alternative, albeit a lower storage capacity. Their strength lies within the major advantages coming, mainly, from their primary exploitation phase: extended geological characterization, knowledge of reservoir dynamics, acquaintance of seal presence and characterization, together with existing infrastructure that can be re-used or re-purposed for CO2 injection .
Within the framework of the UK decarbonization program, three hydrocarbon fields have been investigated for the purpose of the CO2 storage. Those three reservoirs are approaching the end of their production life after 20+ years of continuous exploitation. From a petrophysical standpoint, the three sites lie within the same sandstone, characterized by medium to high porosities (14% to 19% on average) as well as high average permeabilities (from 400 to 2000 mD on average). Reservoir pressure is very low at present date, with foreseen values within the 5 to 10 bar range at their abandonment date: it's worth noticing that, being those reservoir shallow (between 720 and 1000 m TVDSS) their associated temperature TRes is low and proximal to the Critical Temperature TC of the Carbon Dioxide (31.1 °C) as Tab. 1 shows.