STRATIGRAPHIC VARIABILITY AND PETROPHYSICAL CHARACTERISTICS OF THE PENNSYLVANIAN PRUE SANDSTONE AND OSWEGO LIMESTONE, CENTRAL LINCOLN COUNTY, OKLAHOMA

Abstract

ABSTRACTThe Prue Sandstone in Lincoln County, Oklahoma is interpreted to have been deposited in a tidally influenced deltaic environment. The Prue Sandstone consists of three main subenvironments: incised valley fills, distributary channels, and fluvial flood plains. Distributary channels are characterized by light gray, medium to fine grain micaceous sandstones with localized flaser and wavy laminations. Fluvial flood plains exhibit planar laminations to wavy laminations of fine-grained gray sandstone and dark mudstone. Coal in the upper Prue Sandstone is associated with fluvial flood plains. Coal is discontinuous in the study area and separated by sandstones and shales. The Oswego Limestone represents a shallow-marine to marine environment that was situated along a southwest-northeast trending shoreline. The Excello Shale separates the Oswego Limestone and the Prue Sandstone and is thin and continuous across the study area. While both the Oswego Limestone and the Prue Sandstone are known hydrocarbon reservoirs in Lincoln County, Oklahoma, their stratigraphy, sedimentology, and reservoir characteristics have not been extensively studied. Therefore, this study explores the Prue Sandstone and Oswego Limestone structure, lithology, total porosity, effective porosity, water saturation, and bulk volume hydrocarbon through well-log analysis and 3-D geostatistical modeling. In the 224-mi2 (580 km2) study area, >400 wells were used for stratigraphic correlations. Of the 400 wells used for correlations, 198 wells were digitized to provide a combination of gamma-ray, neutron-porosity, bulk-density, and resistivity logs. Two wells close to the study area provide core from selected intervals. Subsurface correlation and mapping and petrophysical analyses of the Prue Sandstone and Oswego Limestone were based on well-log data. The Oswego Limestone and Prue Sandstone thickness vary from ~2–45 ft (~0.61–13.71 km) and v ~50–150 ft (~15.24–45.72m), respectively. Petrophysical analysis of the sandstones within the Prue Sandstone indicate effective porosity values from 1–33% and Sw values from 21–100%. The Oswego Limestone total porosity varies from 0–26% and Sw values range from 20–100%. Three-dimensional reservoir models of the Oswego Limestone and Prue Sandstone illustrate the high reservoir heterogeneity across the study area that is controlled by the stratigraphic variability of lithologies and their depositional trends.