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Evaluation of Offshore Reservoirs for Potential Carbon Sequestration Through an Integrated Basin Analysis— Seismic Stratigraphic Approach: Example-Mid Atlantic U.S.A.


Subsurface marine water-bearing sandstones provide one of the largest potential reservoirs for the sequestration of carbon dioxide (SCD). Delineation of the geometry, reservoir quality and sealing potential of such reservoirs can be facilitated through many of the same workflow procedures as conventional hydrocarbon (HC) exploration, with a few important exceptions. This investigation applied an integrated basin analysis-seismic stratigraphic approach to ~75,000 km2 of the continental shelf of offshore New Jersey and Delaware, using ~300 migrated 1978-1984 vintage 2-D seismic reflection lines and petrophysical logs from 13 exploration wells. To facilitate the interpretation of the seismic, a novel seismic inversion of 2-D stacking velocities was applied to generate 2-D panoramas of velocity, density, porosity, and seismic lithofacies.

The workflow entailed: 1. Interpretation of fault mechanical stratigraphy; 2. Integration of “Vail” and “Galloway” approaches to sequence stratigraphy; 3. Detailed stratigraphic correlation with well micropaleontology; 4. Delineation and correlation of 16 parasequence sets; 5. Basin modeling of real and virtual wells for variations of temperature, porosities, and organic maturities; 6. Basin modeling determination of pressures and shale ductility; 7. Determination of velocity, density, and porosity from seismic inversion; 8. Determination of seismic lithofacies from seismic inversion; 9. Mapping of surfaces; 10. Generation of isochrons and isopachs.

The similarities between conventional HC and SCD reservoir exploration are finding optimal reservoir, delineating top and lateral seals (identifying ductile shale lithofacies), determining subsurface thermal-pressure conditions, and locating structural and stratigraphic traps. In contrast to traditional HC exploration, to optimize SCD potential storage one should search for low shale-to-gouge ratio (“leaky”) faults for maximum reservoir connectivity and potential intra-fault disposal; purposefully examine depleted HC fields; and avoid potentially overpressured reservoirs.

In comparison to maturely explored offshore regions such as the Texas-Louisiana Gulf Coast, a pragmatic evaluation of the SCD potential of a poorly explored offshore region such as the New Jersey-Delaware continental shelf, there is a downside. The paucity of wells and seismic, especially 3-D seismic, detrimentally affect both data quality for subsurface control as well as the lack of pre-existing potential field storage sites. However, there is a potential upside to the SCD evaluation of poorly explored areas with sparse data. In applying workflows common to HC exploration along with new ideas and new technology, new HC play concepts may emerge.

Acknowledgment: This material is based upon work supported by the Department of Energy under Award Number DE-FE0026086.