Depositional and Diagenetic Controls on Reservoir Quality in the Upper Wilcox Sandstone, Fields Field, Beauregard Parish, Louisiana

Stephanie R. Forstner
Ridge Resources LLC, 1485 Florida Road, C204, Durango, CO 81301

Numerous studies have been conducted in the Texas Wilcox trend; however, only a handful of diagenetic and depositional studies have been conducted in the Wilcox Formation of Southwestern Louisiana. Located in this region is Fields Field which has produced from the Upper Wilcox Sandstones since 1966 (approximately 4.4 MMBO and 30 BCFG). One Upper Wilcox Sandstone is a 100 foot thick nearshore marine bar deposit that ranges in depths of 12260-12562 feet. This lithic arkose interval has an average 15% porosity and is productive in Fields Field in only some wells. Depositional and diagenetic processes are principal mechanisms that influence the economic viability of an oil and gas reservoir. The purpose of this study is to understand the depositional and diagenetic processes that affect reservoir quality to improve completion practices and further characterize the Upper Wilcox. The Wilcox has primarily been described as a prograding wave-dominated deltaic system (Galloway 2000). Thirteen Upper Wilcox rotary cores have been analyzed via petrographic thin sections, QEMScan, and SEM. Sands have been mildly to moderately bioturbated perpendicular to bedding and carbonaceous fragments of plant material are present. QEMScan and SEM results reveal primary intergranular and secondary porosity to be occluded by primarily quartz overgrowths, illite, chlorite, and smectite clays. Secondary porosity is a result of alkali-feldspar and other unstable grain dissolution. The highest porosity zones occur with pore-filling and pore-coating illite, chlorite, and smectite clays that make up an average of 32.5% of the total rock composition. The results of this study add insight to the future development of Fields Field and completion practices in tight sandstone reservoirs.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012