ABSTRACT: The Geology of Three Mississippi Fields-Trimble, Thanksgiving and Chaparral (Extension)

MOODY, JACK S., and EDWIN E. STICKER, Office of Geology, Jackson, MS

During the period from 1987 to 1990 a number of new fields and field extensions were discovered in Mississippi. Three of the more significant finds are Trimble Field in Smith and Simpson counties, Thanksgiving field in Amite County, and Chaparral field (extension) in Wayne County.

Trimble field was discovered in 1988 by the Cobra-Paramount #1 Purser (Sec. 17, T10N, R6W). The well was completed in the Stanley Sand of the Eutaw Formation at a rate of 2.76 MMCFGPD and 16.80 BCPD. The Stanley Sand is a very fine-to fine-grained, grayish-green, glauconitic, low-resistivity (<1W) pay sand that averages almost 100 feet in thickness. The reservoir is trapped on the upthrown side of a down-to-the-north fault, juxtaposing the sand against the downthrown Selma Chalk. This structural setting has allowed over 200 feet of gas column to accumulate in the field. The estimated ultimate recovery from the 21 producing wells is 100 BCFG.

In late 1987 Oxy USA drilled and completed the A-1 Jackson (Sec. 17, T2N, R2E) as the discovery well for Thanksgiving field. The well was perforated in the Stringer "A" Sand Member of the Lower Tuscaloosa Formation and was tested at 501 BOPD and 1.9 MMCFGPD. The "A" Sand, which varies in thickness from 20 ft to 70 ft, was deposited as point bars in a fluvial-deltaic environment. The sand occurs within a meander belt oriented northwest-southeast. The stratigraphic trap responsible for the accumulation is formed as the sand pinches out both updip and laterally against an abandoned channel plug and associated flood-plain shales. Prior to the initiation of a pressure maintenance program, the ultimate primary recovery was estimated to be over 2.5 MMBO and 8.0 BCFG. The implementation of th pressure maintenance by injecting and reinjecting natural gas should significantly improve the recoverable reserves. In addition, there is production from the Wilcox and Frio formations.

Smackover production was first established at Chaparral field in early 1990 by the Weeks Exploration #1 Hall Industries (Sec. 24, T10N-R7W). An upper Smackover completion resulted in an initial production rate of 436 BOPD, 265 MCFGPD and 2 BWPD. This well along with the six development wells are located on the southwestern flank of the field, where the upper Smackover is downthrown and juxtaposed against the Louann Salt. The vertical seal is provided by the overlying Haynesville-Buckner anhydrites and carbonates. The primary reservoirs of the upper Smackover carbonate are within zones of enhanced dolomitization as a result of brecciation and fracturing. The Chaparral Field Smackover reservoirs are somewhat unusual in that the better reservoir development occurred in the

mud-supported rock fabric rather than the higher energy grain-supported facies.

AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)