The Challenge for the Coiled-Tubing Industry
Authors: Blount C.G. 
Published: December 2007

Technology Today Series

From Aug. 9 through 14, 1992, approximately 80 individuals from throughout the globe met in a seemingly remote area of the Colorado Rocky Mountains with one common bond: advancement of coiled-tubing (CT) technology. This was the first SPE Forum Series meeting devoted entirely to CT technology. After longdays of sometimes heated debates, the final session found these individuals charged with the task of identifying areas where CT industry development efforts need to be focused "to utilize the untapped potential ofCT."

Numerous ideas and opinions were generated at the SPE Forum Series meeting to create a long list of areas with high leveraging potential (high return on investment) for an oil industry well below the crest of a "boom" cycle. However, from the master list, each individual was given the opportunity to vote for only three issues that they felt were the most pressing. The 17 items that survived the exercise are listed below, "prioritized" by this group's vote.CT drilling technologyStandardized CT fatigue testing and computer modelMaterial, equipment, safety, and maintenance standardsWell-control equipmentCT completion and production equipmentCT material advancementsCT cleanout technologySpecial application CT tools and equipmentHigh-pressure abrasive jet technologyHybrid CT units (special purpose; i.e., CT on rigs)Equipment for operating with and in higher pressuresImproved information exchangeJob planning and operational guidelinesLarger-diameter CT (and peripheral equipment)Simplified hydraulicsFloating operations CT technologyElectronic monitoring and control of CT units.

A year and a half later, where do these leveraging ideas fit into the overall CT industry picture?

CT Drilling, High-Pressure Abrasive Jet Technology, and Hybrid CT Units

Interest in CT drilling is high from a technology standpoint. However, real-world economics of CT drilling are not attractive in many areas. Drilling using a CT unit requires a relatively large investment in specialized equipment to perform the work and the latest in technology to meet the challenge of applying the techniques within the inherent constraints of CT, such as no piperotation, limited pressure cycles, and lower flow rates.

A recent paper devoted to CT drilling reports that 39 wells were drilled or reentered with CT in the last 3 years following pioneering work in Canada during the mid-1970's. Information from Canada reveals a considerably higher number of short-distance, well-deepening CT operations, many of which were underbalanced, and a few wells drilling from surface. Total CT drilled or deepened wells over the last 2-1/2 years is about 200. The latest in CT technology and equipment is competing with decades-old, conventional rotary technology, which requires very few new techniques and has an untold number of fully depreciated rigs available to perform the task. Considering these facts, it is understandable why the economics of the comparison look less than optimal. So why bother?

Fortunately for the CT industry, there are niche markets and a few technological advantages to CT that can make the effort to develop the technology worthwhile. Re-entry work is one natural target for CT units that provides a relatively large potential market. And one often-cited advantage to CT is the smaller footprint and greater mobility of the equipment relative to common rotary rigs. CT advantages, however, come with a significant reduction in operational flexibility that demands the new techniques and tools previously mentioned.

Another potential advantage to CT drilling is the prospect of underbalanced drilling, which is required in very-low-pressure reservoirs and for formation damage mediation. The search for a nondamaging drilling and completion technique is heightening interest in underbalanced drilling in many areas. Recent efforts in Canada and on Alaska's North Slope034,504 focus CT drilling efforts toward this goal with some encouraging results. In a recently completed North Slope well, penetration rates of 100 ft/hr and initial production rates300% higher than anticipated were realized when actual under balanced conditions were achieved during portions of the CT drilling process. The underbalanced conditions were achieved using gas lift in the existing 4 1/2-in. production string. Interestingly, previous attempts in Alaska at achieving underbalanced conditions during drilling were unsuccessful, partly because of a conservative gas-lift design coupled with inaccurate tubing-hydraulics model predictions.

Shallow-length CT deepening operations are cost-competitive with a conventional rig in most areas.

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