SPE Members Abstract An investigation into the feasibility of drilling openhole with coiled tubing indicates that such operations are feasible using currently-available technology. The study covers aspects of the drilling operation, including bottomhole equipment, surface equipment, coiled tubing unit,, drilling logistics and cost. The conclusion is made that coiled tubing drilling operations can provide benefits in terms of safety, provide benefits in terms of safety, formation damage and economics. Introduction The first coiled tubing unit was developed by Bowen Tools in 1965. The unit was used on Navy submarines to deploy a mile long, 1/2 inch diameter tubular antenna. The technology was rapidly adapted for oilfield use. The early units utilized the 1/2 inch diameter tubing from the original design. As popularity of the units increased, larger tubing capable of higher flow rates and deeper operation was developed. The largest coiled tubing unit commercially available to date is 1–3/4 inch and an operating depth of 24,600 feet has been recorded. Drilling with coiled tubing is not a new concept. Workover operations using small diameter positive-displacement motors have been positive-displacement motors have been performed since the early 1970's. The performed since the early 1970's. The recent development of more reliable, more powerful slimhole drilling motors and associated drilling equipment has greatly increased the success rate of such operations. The results of this study indicate that drilling openhole with coiled tubing can provide substantial long-term benefits with minimum development costs. Coiled tubing drilling will probably be the next major advance in probably be the next major advance in new drilling technology. P. 551

Wells with small liners occasionally require unique methods of drilling, completion, and reworking, especially deep-hole wells and wells with severe doglegs. Innovative drilling procedures were used successfully on two wells with those downhole conditions. On the first well, cement was drilled in a 3'h-in. liner with a small mud motor and heavyweight mud. On the second well, a large mud motor was used as a downhole power swivel to drill in a 3'h-in. liner. Both jobs were completed at depths of 13,000 to 20,000 ft with mud weights> 18 Ibm/gal and bottomhole temperatures (BHT's) > 300°F.

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. Introduction 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. P. 645