Porosity-Permeability Trends, Sparta B Sandstones (Eocene), Fordoche Field, Pointe Coupee Parish, Louisiana

KRUTAK, PAUL R., Basin Research Institute, Louisiana State University, Baton Rouge, LA

Fordoche field, Pointe Coupee Parish, Louisiana (44 wells) contains at least ten hydrocarbon-bearing zones. Major reserves of bypassed oil probably exist in the shallowest reservoir, Sparta B, estimated to contain approximately 5.6 mm STB OIP and 2.0 bcf GIP. Sparta B pay thicknesses average 15 ft with 24.7% porosities and 200 md permeabilities. Other averages include: 7980 PSI BHP (abnormal range), 228 degrees F BHT, 2075 PSIG bubble point pressure, gas-oil ratio 500 SCF/bbl, oil gravities 40-44 API.

Interpretation of lithology and sedimentary structures of conventional core cut from 11,330-11,380 ft in the lower part of the Sparta-B-producing interval in the Clayton Williams Seymour Dreyfus Number 1 (Sec. 31, T6S, R8E), IP 395 BOPD and 79 BWPD, reveals this section consists of upper shoreface sandstones capped by storm washover sandstones and lagoonal mudstones. Underlying lithofacies are lower shoreface and inner shelf siliciclastics.

Petrographic, SEM, and EDX study of 20 thin sections from these units discloses the following down-core trends and petrofacies: (1) high porosity (20-25%)-permeability (250-500+ md), fine- to very fine-grained quartzarenites whose pore throats average about 10 microns comprise the storm washover deposits. Vermicular chlorite begins to occlude porosity near the bottom of this unit (11,338.25 ft); (2) pore throats of 10-20 microns occur in quartzarenitic, upper shoreface sandstones that display slightly lower porosity and permeability than overlying units. Kaolinite and chlorite begin to occlude porosity in this facies (11,346.00 ft and 11,347.50 ft); calcite completely occludes porosity at 11,350.46 ft; (3) lower shoreface sandstones are increasingly organic, mostly very fine sand size Organic lamellae parallel to bedding are characteristic with pore throats in the 10-15 micron-size range; chlorite and calcite occlude porosity at 11,360.50 ft and 11,365.00 ft, respectively; (4) inner shelf lithologies are very fine-grained, highly organic, micaceous, poorly sorted quartzarenites with virtually no permeability. Pore throats are small (approximately 10 microns). Biotite occludes porosity at 11,374.67 ft, muscovite at 11,375.79 ft.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)