Shell Petroleum Dev. Coy. onshore wells in Nigeria are from brown fields producing since 1960. The fields have about 300 flowing strings. The fields are characterized by various challenges including depleted reservoir pressures, some non-mandrel wells, single and dual string completion with or without sand control, old tubulars and low remaining oil reserves. The crude is medium to high API gravity, all ranges of viscosity and produced with high water cut in some cases.

These wells completed without mandrels were either not flowing because of one or a combination of 1) formation damage problems 2) vertical lift problems due to depleted reservoir pressures and increasing water cut and 3) high pressure drop across flow lines in wells far from the flow stations. Distance becomes a significant factor especially with remote manifold wells that also suffer high backpressures from healthy common manifold wells. The predominant damage mechanisms in these wells are fines migration, clay swelling, wettability changes, water block, inorganic and organic scale deposition.

Restoring the productivity of non-mandrel wells with vertical lift problems or insufficient energy to reach flow stations with the aid of artificial lift methods (gaslift being the most accessible and cheapest option) in these fields would normally require a workover rig. Wells were worked over and re-completed with gaslift mandrels when significant reserves still existed. An expensive uneconomical option in these brown fields with dwindling reserves. The alternative, which is the rimless pack-off mandrel or insert orifice, has not only been found economical but also a technically less risky and skilful approach to introduce gaslift assistance. At the onset of the introduction of the insert orifice technology in the fields, engineers were faced with the challenge of determining the best position in the tubing for inserting the gas lift orifice in order to maximize reserves recovery. Using the poor boy approach of creating an inlet for gaslift into the production tubing easily became a short term and un-sustained success.

The case specific insert orifice design was applied in old non-mandrel wells with single and dual string completions, with or with sand control in depleted reservoirs and with low remaining oil reserves. The results so far have been 100 percent success in production increase and reserves addition. 11 strings have been successfully put on gaslift using the case specific design insert orifice method. These wells have delivered over 3.3MMstb of oil at a low average Unit Technical Cost of ca. 0.8$/bbl. The approach has saved the company the high cost of workover operations that would otherwise have been required, increased ultimate recovery and also improved the insert orifice gas lift design in general.

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