Abstract

In Algeria about 60% of the proven oil reserves are in the Hassi Messaoud region which was discovered in the 1950's. Several oil production wells drilled over 40 years ago have been shut in and are awaiting workover plans to revive those wells and get them back into economic production. A typical workover program is comprised of extending the open-hole in the reservoir zone, below 7-inch casing, and producing that through a new 4-1/2-inch perforated production liner. At the time of initial drilling of those wells, the reservoir pressure was as high as that of the shale zone immediately above it. This reservoir pressure has now declined and can be found to be as low as one-third of the shale formation pressure.

This recent variation in formation pressures (between exposed shale and reservoir zones) has created a need to mechanically isolate this exposed shale zone immediately above the lower pressure reservoir prior to drilling ahead. Original workover programs required the use of an additional (smaller size) casing string for this purpose, with the eventuality of drilling the reservoir open-hole section with a much smaller hole-size and completing the well as with a slim-hole configuration.

This paper presents an alternative solution that was implemented to workover these type of wells and enable completion with a sufficient hole-size in the producing zone to avoid a slim-well configuration. The major technology used to facilitate this alternative workover was the installation of a solid expandable open-hole liner to mechanically isolate the high pressured shale zone above the reservoir. The aim was to still allow for a large enough open-hole passage in to the reservoir section to facilitate the use of high performance directional drilling BHA assemblies,

The overall application of this workover is discussed to detail and highlight the added-value solid expandable liners provide in such workover applications. The successful integration and planning of the solid expandable installation along with; short radius casing exit, zonal isolation, and enhanced directional drilling has proven to be a significantly superior technical and economic alternative solution.

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