A reservoir management study of a mature oil field

Abstract

An integrated geological, petrophysical and reservoir engineering review was performed for a mature, producing oil field. Like many older fields, important data are missing or were not collected. The techniques used in this thesis may be applied to other mature oil fields to make sound engineering and business decisions. I interpreted the geological structure and stratigaphy of the salt dome oil field. Structure, isopach and cross-sectional maps were constructed. Depositional environments of the producing horizons were identified. Potential for additional reserves was assessed. Well logs, core data, water resistivity and produced fluids data were analyzed. Average values of porosity, permeability, and oil saturation were determined for the field. Potential reserves behind casing were identified. Based on the revised geological and petrophysical data, the original oil in place was estimated from volumetrics to be 42.3 MMSTB. Cumulative oil production was determined for the first time since 1963. The field, individual reservoir, and individual well production performances were reviewed. Initial production histories of more than 220 wells were documented. I collected wellhead fluid samples and analyzed oil gravity and viscosity. Other fluid properties were estimated from correlations. Pressure data from the field was collated and analyzed. Primary production mechanisms and aquifer influx were estimated by reviewing early producing history and performing material balance calculations. Water influx was calculated. The performances of analogous salt dome reservoirs were compared to that of the field. All past well stimulations were reviewed and suggestions made for better implementation. Water injection in the field was reviewed. Problems of implementation and reservoir response were identified. The best areas in the field for waterflooding were identified and analyzed with an analytical model. Based on existing development, the oil ultimate recovery is estimated to be 14.4 MMSTB or 34.0 % of original oil in place. To determine whether oil recovery can be improved, incremental, after tax economic analysis was applied to several schemes. Infill drilling, hydraulic fracturing and waterflooding were analyzed. A course of action to maximize economic return is outlined for the field. Hydraulic fracturing appears to be the most viable technique to improve oil production from the field.