Selection and Characterization of Geological Sites able to Host a Pilot-Scale CO₂Storage in the Paris Basin (<i>GéoCarbone</i>-PICOREF)

The objective of the GéoCarbone-PICOREF project was to select and characterize geological sites where CO<sub>2<sub/> storage in permeable reservoir could be tested at the pilot scale. Both options of storage in deep saline aquifer and in depleted hydrocarbon field were considered. The typical size envisioned for the pilot was 100 kt CO<sub>2<sub/> per year. GéoCarbone-PICOREF initially focused on a “Regional Domain”, ca. 200 × 150 km, in the Paris Basin. It was attractive for the following reasons: detailed geological data is available, due to 50 years of petroleum exploration; basin-scale deep saline aquifers are present, with a preliminary estimate of storage capacity which is at the Gt CO<sub>2<sub/> level, namely the carbonate Oolithe Blanche Formation, of Middle Jurassic age, generally located between 1500 and 1800 m depths in the studied area, and several sandstone formations of Triassic age, located between 2000 and 3000 m; several depleted oil fields exist: although offering storage capacities at a much lower level, they do represent very well constrained geological environments, with proven sealing properties; several sources of pure CO<sub>2<sub/> were identified in the area, at a flow rate compatible with the pilot size, that would avoid capture costs. 750 km of seismic lines were reprocessed and organized in six sections fitted on well logs. This first dataset provided improved representations of: the gross features of the considered aquifers in the Regional Domain; the structural scheme; lateral continuity of the sealing cap rocks. An inventory of the environmental characteristics was also made, including human occupancy, protected areas, water resource, natural hazards, potential conflicts of use with other resources of the subsurface, etc. From all these criteria, a more restricted geographical domain named the “Sector”, ca. 70 × 70 km, was chosen, the most appropriate for further selection of storage site(s). The geological characterization of the Sector has been as exhaustive as possible, with the reprocessing of additional 450 km of seismic lines, and the collection of a complete well-data base (146 petroleum wells). At this scale a relatively detailed characterization of the sedimentary layers could be done, in particular the formations potentially rich in aquifer units. For the Middle Jurassic carbonates observations were made on analogue sediments outcropping 150 km to the east of the Sector. A geological and numerical 3-D representation of the whole sedimentary pile of the Sector area was built. It forms a basis for constructing grids used by codes able to simulate various processes induced by CO<sub>2<sub/> injection (displacement of the fluids, pressure build-up and release, mechanical deformation, mineral interactions, control of the parameters used to check the local sealing efficiency, etc.). In parallel with that work on aquifers, GéoCarbone-PICOREF has access to all the petroleum data, including production data and reservoir modelling, of the Saint-Martin de Bossenay oil field, localized in the eastern part of the Sector. This was an opportunity to apply a comparable methodology and to test the capabilities of modelling codes to the specific case of a depleted hydrocarbon field, and to show some of the advantages of such a context with respect to a pilot-scale CO<sub>2<sub/> injection.