Deep-Water Reservoir Characterization Using High Resolution Formation MicroImager, Conventional and Sidewall Core Data, SEM and Thin Section Petrography from Mississippi Canyon 397 Field

Allen E. Evans

High resolution Formation MicroImager (FMI) logs were included in the formation evaluation program for several deep-water reservoirs in the Mississippi Canyon 397 field, Offshore, Louisiana. In addition to resolving structural dip and large faults; depositional features and sedimentary structures were easily discernible on the image. Micro faults, trough-crossbeds, small scale bedding, scour surfaces and shale rip-up clasts are common throughout the reservoir. Convolute bedding and dewatering structures have also been interpreted. Many of the depositional features recognized on the FMI are not identifiable by conventional logging practices.

Thinly bedded cyclic sand/shale packages predominate the bottom section in one reservoir. Sidewall cores, thin section petrography and SEM data indicates that the sands in these packages are exceedingly clean and well sorted, with little to no clays. Permeabilities of 500 to 2500 millidarcies are common with porosity values approaching 30%. Several low resistivity and moderate gamma ray zones within these reservoirs have abundant amounts of very fine sand, silt and clays. These low resistivity zones have low permeabilities resulting from clays being deposited with the fine sands and silt and subsequently clogging pore throats.

Sedimentary features observed on the FMI image are believed to be associated with rapid sediment deposition from low density turbidity flows, with low resistivity/moderate gamma ray zones representing the last stage of each flow. Sand in these low density flows exhibit excellent reservoir quality even when highly laminated and thinly bedded.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995