Numerical Approach to Optimising Oil and Gas Production in Thin Oil Rim Reservoirs

Abstract

The development of a thin oil rim can involve complications in the oil production due to severe gas and/or water coning events.<br>This paper deals with a Nigerian oil and gas multilevel field where some of the levels bear a thin oil rim associated with a large gas cap. After a few years of production from three oil levels, it was decided to develop all gas and oil levels, to increase the oil production rate and satisfy the increasing demand for gas. Therefore, the thin oil rim reservoirs were considered as potential sources of oil and gas reserves.<br>A 3D black oil simulation model was built to study the development of the whole field. Gas PVT data were characterised through the vaporised oil gas ratio to simulate the effects of depletion on the condensate stream during production from gas levels.<br>Sensitivity runs were performed to investigate the development of the oil rim reservoirs. The model indicated that the wells located in the oil rim were affected by high water cut, whilst the wells in the gas cap area and far away from the oil rim, could produce large gas rates without draining the oil in the rim.<br>An intermediate location was considered in the gas cap flank close to the oil rim. The wells with this location showed early high gas production with condensate decline, followed by liquid hydrocarbon production increase with gas rate reduction. During the early time, the condensate production fell due to depletion. Afterwards, the liquid hydrocarbon rate started to increase since wells drained the oil rim through coning.<br>The results of the simulation encouraged the development of the thin oil rim reservoirs mainly through these intermediate locations to optimise both oil and gas production.<br>