Publications

Through-tubing workovers present an attractive solution to develop the marginal reserves, which otherwise would not be developed. With an increasing availability of different through-tubing formation evaluation tools and perforation guns, the quest to rejuvenate the old wells is greatly enhanced.The objective of a completion is a compromise of high productiviw, longevity and allowance for future operations, in order to maximize the profit. Substantial reserves were sometimes intentionally left behind pipe due to economic and engineering reasons. Less-productive intervals were often deferred to later in the well's life in order to maximize highproductive intervals. Moreover, old wells were sometimes completed without allowance for future economic workover operations.A full-scale workover, where all the tubing is pulled out, is sometimes not economic and is also a highly risky operation. The reserves are often marginal to justify the workover. With the continuously decreasing well production, any potential reserves remaining in the well are worthy of another review.In a producing field, the reservoirs arc in a dynamic state with contacts constantly changing, depending on the reservoir drive and the fluid withdrawal rate. It is not surprising that the current fluid saturations are not the same as when the well was open hole logged. Determining hydrocarbon saturations behind casing is now possible without the need to pullout the existing tubing. A wireline-conveyed RST (Reservoir, Saturation Tool), run through-tubing, enables the fluid saturation measuremeni.. Intervals chosen can then be perforated with through-tubing guns.This paper discusses the workover unit and the through-tubing tools (i.e. RST, perforating guns). Several examples of through-tubing workovers highlight the usefulness of through-tubing workovers in rejuvenating old wells.