--> Abstract: Multi-Lateral Horizontal Well Application for Improving the Oil Recovery of a Mature Field, Intisar 103N, Libya, by Mohamed M. Gharsalla and Mohamed B. Elghmari; #90077 (2008)

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Multi-Lateral Horizontal Well Application for Improving the Oil Recovery of a Mature Field, Intisar 103N, Libya

Mohamed M. Gharsalla* and Mohamed B. Elghmari
Zueitina Oil Company, Libya
*[email protected]

This presentation examines the performance of a horizontal well with multi-lateral completion in the mature Upper Sabil Reservoir in the Paleocene Zelten Formation in Intisar 103N field. The hydrocarbon trap in an anticline that houses 14.4 million stock tank barrels (MMSTB) of oil-initially-in-place. The reservoir is highly under-saturated with oil of 42° API gravity. The initial field development with a vertical well resulted in a poor recovery, 1.3 million barrels of oil in 19 years of production (equivalent to a recovery factor of 9%). The recovery mechanism in the reservoir is mainly rock-fluid expansion with marginal support from flank aquifers. The poor recovery can be attributed to thin pay thickness, poor reservoir quality, large well spacing, and the lack of pressure support from aquifers. The vertical well revealed a nearly constant production rate for the last 17 years indicating the drainage area is much larger than one well can deplete in a reasonable time frame. The incentive of reducing well-spacing existed but the question was how to reduce the well spacing: by drilling many vertical wells or a lesser number of horizontal wells?

A reservoir simulation study in 2003 indicated that drilling vertical wells in a very thin reservoir of poor quality was not cost-effective. Hence, an horizontal well was drilled and completed at the top of the porosity zone with two lateral legs extending 1,632 and 2,811 ft. Two lateral sections were branched-out from the same spot in the well with a 47° angle between them and completed open-hole in the reservoir. The stabilized oil production rate of the horizontal well was approximately three times greater than that of the vertical well, whereas the drilling cost of the horizontal well was about 1.3 times higher. The production from the horizontal well showed no negative impact on the production performance of the existing vertical well. The oil reserves, as a result of putting the horizontal well on stream, are expected to increase by 1.8 million barrel. It is evident that horizontal wells with multi-lateral completions can improve oil recovery, accelerate oil production and reduce production cost. The reduced pressure gradient in the reservoir, near the wellbore associated with the long completion intervals, reduced the water-coning and eventually production cost.

 

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain