Sequence Stratigraphy and Reservoir Characterization of Cranfield Field, Mississippi—An Enhanced Oil Recovery and Carbon Sequestration Study

Cranfield field, Mississippi, was discovered in 1946 and abandoned in 1965 at the end of primary production. Denbury Resources, Inc. now owns the field and is currently in the final preinjection stages of a CO2 EOR flood. Denbury is hosting the Gulf Coast Carbon Center on a US Department of Energy sponsored research study of the feasibility of injecting and sequestering CO2 into the Tuscaloosa reservoir.

The traditional lithostratigraphy used to describe the Tuscaloosa at Cranfield comprises five informal units named A through E. Basal D and E units, commonly called the Tuscaloosa massive, comprise medium to coarse sandstone and granule to pebble conglomerate with abundant chert. Core and well log facies indicate the Tuscaloosa at Cranfield has a sharp basal contact. Limited available core and wireline-log data indicate much finer grained sandstone, siltstone, and mudstone below basal Tuscaloosa contact. Internal architecture of lower Tuscaloosa is more complex than traditional A, B, C, D, and E lithostratigraphy. High-frequency correlations indicate multiple incision events within an overall upward-fining succession from basal contact upward to a thick marine mudstone section, the so-called marine Tuscaloosa. According to sequence stratigraphic principles, the sharp basal contact and coarse-grained nature of basal units (a braided-stream–braid-plain depositional system) indicate a lowstand systems tract that grades upward into a fine-grained marine succession (a transgressive systems tract, TST). The lowstand incises into an underlying highstand systems tract, HST. The sharp basal contact is a sequence boundary. A maximum flooding surface constitutes the top of the TST within the marine Tuscaloosa. An overall upward-coarsening succession above the maximum flooding surface indicates an overlying HST. Sequence stratigraphic principles predict that the remaining components of the lowstand systems tract (i.e., basin floor fan, slope fan and prograding complex) should occur basinward of the Cranfield locality, beyond the current study area.