A petrophysics and reservoir performance-based reservoir characterization of Womack Hill (Upper Smackover) Field (Alabama)

Abstract

Womack Hill is one of the 57 Smackover fields throughout the Gulf Coast region. Since its discovery in 1970, Womack Hill Field has produced 30 million STB from the Upper Smackover sequence of carbonate reservoirs. Since production reached its peak in 1977, oil and gas rates have declined substantially. During the last ten years, the production decline has accelerated despite an increase in the water injection rate. This production decline along with the increase in the operating costs has caused a considerable drop in profitability of the field. The field currently produces 640 STB/D of oil and 330 MSCF/D of gas, along with 6,700 STB/D of water, which implies a water cut of over 90 percent. In order to optimize the reservoir management strategies for Womack Hill Field, we need to develop an integrated reservoir study. This thesis addresses the creation of an integrated reservoir study and specifically provides a detailed reservoir description that represents the high level of heterogeneity that exists within this field. Such levels of heterogeneity are characteristic of carbonate reservoirs. This research should serve as a guide for future work in reservoir simulation and can be used to evaluate various scenarios for additional development as well as to optimize the operating practices in the field. We used a non-parametric regression algorithm (ACE) to develop correlations between the core and well log data. These correlations allow us to estimate reservoir permeability at the "flow unit" scale. We note that our efforts to reach an overall correlation were unsuccessful. We generated distributions of porosity and permeability throughout the reservoir area using statistically derived estimates of porosity and permeability. The resulting reservoir description indicates a clear contrast in reservoir permeability between the western and eastern areas - and in particular, significant variability in the reservoir. We do note that we observed an essentially homogenous porosity distribution. We provided analysis of the production and injection data using various techniques (history plots, EUR plots, and decline type curve analysis) and we note this effort yielded a remaining recoverable oil of 1.9 MMSTB (under the current operating conditions). This analysis suggests a moderate flow separation between the western and eastern areas and raised some questions regarding the suitability of the hydraulic "jet pumps" (the water rate increased coincidentally with the installation of the jet pumps).