In the effort to reduce costs, many companies are investigating the cost effectiveness of completing some types of workover operations without removing the production tubing. These operations include scale removal, frac sand removal, squeeze-reperfing, underreaming and junk/fish removal. All of these operations are currently feasible using either slimhole work strings or coiled tubing in conjunction with slimhole PDM's. This paper describes the tools and procedures used to complete these operations and compares their cost effectiveness with conventional operations. A section is included on new tools being developed which should broaden the scope of these operations. The paper concludes that slimhole workover drilling operations can provide substantial economic benefits compared to conventional workover methods.


The introduction of coiled tubing and snubbing units has changed the art of workover operations. The addition of recently developed, powerful, reliable Slimhole positive displacement motors has further expanded the usefulness of these units. Many drilling operations can be perform without removing the production tubing. Common uses for this equipment include obstruction removal inside the production tubing. The obstructions production tubing. The obstructions may range from frac sand to stuck packers. Technological advances are packers. Technological advances are rapidly expanding the applications for Slimhole drilling equipment. Recent successful developments include coiled tubing underreaming and the downhole power swivel. The under reamers allow full-bore clean-out the casing below the production tubing. The downhole power swivel allows the safe utilization of small diameter workstrings.

On the horizon, coiled tubing fishing and openhole drilling with coiled tubing are new methods which will likely be tested in early 1991.

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