Subsurface Study of Lower Tuscaloosa Formation at Olive Field, Pike and Amite Counties, Mississippi: ABSTRACT

Abstract

ABSTRACT Olive Field is located on the Amite-Pike County line in southwestern Mississippi. The field was discovered by Shell Western Exploration and Production Inc., and produces from a sandstone within the Lower Tuscaloosa Stringer Member; the trap is stratigraphic. The Stringer Member consists of alternating sandstones, siltstones, and shales, which have an average thickness of 230 ft (76 m) at Olive Field. The Stringer Member is a transgressive sequence deposited on eroded Washita-Fredericksburg sediments and is overlain by Middle Tuscaloosa marine shales. The coarse-to fine-grained sandstones are quartz-rich with a high percentage of sedimentary rock fragments. The majority of sandstones are shale arenites. However, a large number of rock fragments were badly altered; these fragments could not be identified with confidence; many may be of volcanic origin. The sandstones are cemented by quartz overgrowths, Fe-rich carbonate cement, and chlorite. Sandstones commonly have a high preserved interparticle porosity that is characteristic of Lower Tuscaloosa sandstones. This interparticle porosity is attributed to chlorite, which occurs as an isopachous cement that coats grains and reduced nucleation sites for quartz overgrowths. The Stringer Member was subdivided into five zones in this study based on lithology and electric log responses. The lower three zones were deposited in a fluvial environment. The sandstones were deposited as point bars and channel sands in a meandering system. Siltstones and shales represent overbank, flood basin, and channel fill deposits. The upper two zones consist of sediments deposited at or near sea level. Finely laminated shales and siltstones represent marsh and bay deposits. The topmost zone is a thin continuous sand body that represents a remnant beach deposited before major marine transgression.