Following a pilot horizontal well completed in November 1988, five horizontal wells were drilled in the Erb West field off-shore East Malaysia by Sabah Shell Petroleum Company (SSPC) during 1990. Another three horizontal wells are planned to be drilled in 1991. The objective of the wells is to develop a 40 m thick oil rim, maximising the oil recovery and offtake rates, while delaying gas and water breakthrough.

Drilling short pilot holes at the entrance of the horizontal section to establish accurately the depth of the fluid contacts is important to achieve optimum placement of the horizontal hole with respect to the contacts. It is preferred to drill wells perpendicular to the strike of the formation rather than parallel to the strike in order to penetrate and drain several stacked sands. Removal of the TCP guns after perforation allowing for diagnostic surveys and remedial work is preferred. Flowing build-up surveys yield good results when performed using a down hole shut-in device.

The horizontal wells produce at substantially higher rates than comparable conventional wells and PIF's range from 2 to 8. The horizontal wells seem to be more prone to gas than to water breakthrough, which indicates that tonguing is predominant over cresting phenomena in the Erb West environment. Drilling horizontal wells in a thin oil rim distributed over several stacked sands is an attractive alternative to a conventional development and can increase the ultimate recovery of the field. Small and poor reservoirs can be developed which would remain undrained with a conventional development.

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