Acquisition of an Elevated Pressure Core in a Gas Flooded Carbonate Oil Reservoir: Design and Operational Challenges

Abstract

Abstract Pressure core is the gold standard of reservoir saturation determination retaining gas and oil in an enclosed container preventing hydrocarbon loss to the mud system during retrieval of the core to surface. The technique is underutilized in the oil industry due to safety concerns, short coring lengths (3 to 7 feet) per trip and small core diameters (1.6 to 2.6 inches). A new elevated pressure coring system addresses these concerns. The system does not maintain true formation pressure but reduces the core barrel pressure to less than 1,000 psia for safer working conditions on surface. Upon arrival at surface, the core barrel and accompanying gas/liquid collection canisters are blown down and gas/liquid volumes measured and analysed. Free oil is gathered and stored for later analyses. Core diameter is 4 inches and core length is 10 feet. Zakum Development Company (ZADCO) operates a gas injection pilot in a large carbonate oil reservoir. There was a need to determine field remaining oil saturation after gas flood (ROSg) in a gas injection pilot. Pressure coring was selected as the best technology to obtain this data. This paper covers the planning and implementation of a successful elevated pressure coring operation in the U.A.E., the operational aspects, special core handling techniques, issues encountered and solved. Recommendations are made for future pressure coring operations. A follow up paper will cover the core and fluid analyses aspects.