Proposal Coiled tubing (CT) has evolved in recent years to include more complex applications in drilling and remedial work. As wellbores have extended deeper, the challenges of intervening with CT have increased. For years the limitation in CT work was the coiled tubing itself. However, with advancements in metallurgy and manufacturing processes, the applications where CT can be utilized have expanded to include deeper, hotter, and more complex wellbores. The challenges of performing this work have now been directed at providing reliable equipment. One of the main challenges in these more hostile environments is temperature. At elevated temperatures, work performed with motors becomes very erratic and unreliable. To perform this work, alternate methods have to be analyzed. One solution is the use of downhole turbines or turbodrills. Turbodrills have been used in the drilling industry for decades. It is only recently, however, that the benefits derived by turbodrills have been applied to CT for drilling and workover operations. With the remedial work CT is now required to perform, turbodrills are a natural fit as they address the issues which limit motor performance. This paper analyzes the applications and developments in turbodrills with analysis of recent runs on CT. Introduction Over the last 15 years, CT has expanded to encompass a broad range of applications, which, previously only rotary rigs could execute. These applications range from CT's original intent for workover and remedial operations, albeit with much greater capabilities today than when originally introduced, to drilling grass root wells, completions, and pipelines. As with many oilfield products, it was during the 1980's that CT made great advancements. Materials science was progressing to new frontiers and, with new materials, coupled with better manufacturing and quality processes, the CT itself became stronger and larger in diameter. These two combinations pushed the envelope where CT could be reliably utilized for deeper and more complex applications. It was also in the mid 1980's when focused efforts on reducing costs associated with extracting hydrocarbons became more closely scrutinized. The evolving reliability of CT exemplified a low cost alternative for remedial operations versus a standard workover or drilling rig. At a fraction of the traditional cost, remedial operations could be undertaken to improve recovery rates, with the added benefit that said operations could be undertaken without killing the well. Identifying the shortcomings then proved quite simple: the functionality and flexibility of tools deployed on CT were surpassed by the CT itself and focused efforts were required to design downhole tools specifically for CT.1 It wasn't long before the economic benefits of using CT were translated to the drilling environment. The benefits were numerous: smaller footprint, smaller volumes of drilling fluids to be handled, smaller volumes of drill cuttings requiring handling, faster rig up time, faster tripping time, reduced noise levels, and fewer personnel requirements. All of these led to an overall reduced environmental impact and generally a safer operation.2 An underlying benefit of drilling with CT is Underbalanced Drilling (UBD). This benefit was realized at an early stage in remedial applications, as workover operations could be carried out without introducing kill fluids into the wellbore. By design, drilling with CT fits perfectly with UBD operations, provided penetration rates are adequate and reservoir targets can be hit. Coiled Tubing Drilling (CTD) has evolved dramatically in the recent past. Initially operations were limited to extending existing wellbores. These operations have been commonplace in Alaska for many years. In the early 1990's the challenge of drilling grass roots wells began. By the turn of the century many of the challenges pertaining to this operation had been overcome and today over 7,000 wells have been drilled with CT, with approximately 750–850 new wells being added each year.3

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Proposal The uses for coiled tubing (CT) have expanded over the last two decades to encompass more broad based applications than ever before. This coincides with advancements in drilling technology that have extended these applications to deeper depths, in more hostile environments, the drilling of more complex well profiles, and CT drilling at shallower depths. CT technology has had to keep pace in order to perform effectively in workover operations, and in drilling operations such as sidetracking, wellbore extensions and grass roots drilling, in these more hostile environments. Technology has been adapted to CT as it has been required. However, in many instances, these adaptations have fallen short of achieving optimal performance. The use of Turbodrills is a prime example of this unrealized potential. Using Turbodrills in CT applications provides many benefits, but, historically, a standard Turbodrill, configured for drilling, has been taken off the shelf for use on CT. This method can and has been successful. However, by analyzing the specific applications encountered with CT, Turbodrill design enhancements can be made to better match the Turbodrill to CT applications. One major advancement in this area, is the creation of a Turbodrill that can provide more power with a shorter tool. This paper will detail the design enhancements made to the Turbodrill to accomplish the goals of establishing a shorter tool, with more power, to address current and future applications. Introduction CT technology has progressed dramatically over the last two decades to include a much broader range of applications than ever before. These applications range from CT's original intent, for workover and remedial operations, albeit with much greater capabilities today than when originally introduced, to wellbore extensions, sidetracking, drilling grass root wells, completions, and pipelines. It was during the 1980's that CT technology made great advancements. Materials science advancements, coupled with better manufacturing and quality processes, allowed the CT itself to become more durable, with the added ability to be manufactured in larger diameters. These advancements enabled CT to reliably be deployed in deeper, more complex applications.1 In the mid 1980's, efforts on reducing the costs associated with extracting hydrocarbons became more closely scrutinized, as commodity prices plummeted to historical lows. The evolving reliability of CT exemplified a low cost alternative, versus a standard workover or drilling rig. At a fraction of the traditional cost, remedial operations could be undertaken to improve recovery rates, with the added benefit that operations could be performed without killing the well. Identifying the shortcomings of this new approach then proved quite simple: the functionality and flexibility of tools deployed on CT were surpassed by the CT itself and focused efforts were required to design downhole tools specifically for CT.2 During the 1990's, other technologies, such as 3D seismic, identified numerous bypassed reserves around existing wellbores, left behind due to sweep inefficiencies, smaller reservoirs behind pipe, and deeper reservoirs below previously set casing shoes. The identification of these vast reserves, coupled with technological advances in drilling, and the existing production infrastructure, made it economically feasible to target many of these hydrocarbons. Once again, advances in drilling with CT provided a feasible backdrop to tap these reserves. Numerous benefits of the use of CT could be realized in these applications; smaller rig footprints, smaller volumes of drilling fluids to be handled, smaller volumes of drill cuttings requiring handling, faster rig up time, faster tripping time, reduced noise levels, fewer personnel requirements, reduced environmental impact, safer operations and, ultimately, drilling underbalanced.3

Commercial introduction of Microhole Technology to the gas and oil drilling industry requires an effective downhole drive mechanism which operates efficiently at relatively high RPM and low bit weight for delivering efficient power to the special high RPM drill bit for ensuring both high penetration rate and long bit life. This project entails developing and testing a more efficient 2-7/8 in. diameter Turbodrill and a novel 4-1/8 in. diameter drill bit for drilling with coiled tubing. The high-power Turbodrill were developed to deliver efficient power, and the more durable drill bit employed high-temperature cutters that can more effectively drill hard and abrasive rock. This project teams Schlumberger Smith Neyrfor and Smith Bits, and NASA AMES Research Center with Technology International, Inc (TII), to deliver a downhole, hydraulically-driven power unit, matched with a custom drill bit designed to drill 4-1/8 in. boreholes with a purpose-built coiled tubing rig.

Oil sands applications are well known to be one of the most demanding drilling environments in the industry with regard to durability. The bodies of the cutters and the body of the bit experience severe wear in these applications, leading to inconsistent drilling performance. Extensive efforts in the past decade to solve this issue have been met with limited success. In oil sands applications, the sands are highly abrasive and unconsolidated. The result is that the sand particles quickly become suspended in the drilling fluid and mimic the effect of sandblasting the bit for the duration of the run. In many cases, the bit body wear around the cutters is extensive enough to cause premature bit failure due to cutter loss. The bodies of the PDC cutters themselves also suffer extreme material loss, which leads to cutter breakage and an associated reduction in drilling performance. Finally, in the lateral interval, the sands in cutting beds lying on the low side of the hole cause serious wear to both the gage and backreaming portions of the bit. This paper will discuss new technologies that have proven to eliminate bit wear in the horizontal reservoir interval. Comparisons will be made detailing the severe wear experienced with conventional bits and the absence of wear experienced with identical bit designs using a new body construction technology. A novel PDC cutter will also be presented that has been developed to eliminate cutter body wear. The requirements for improving drilling performance in oil sands applications are as unconventional as the wear experienced in these applications. Unlike traditional applications where improving performance includes an effort to drill faster or further, oil sands applications are typically control drilled and the entire interval is almost always completed in one run. The focus in these applications to augment performance is to improve directional control, enhance backreaming efficiency and hole quality, and increase bit durability. The new technologies detailed in this paper have proven to dramatically enhance each of these key performance indicators, resulting in the ability to drill further and faster, while improving the possibility of success of the well completion.