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
NEW VESSEL FORMATION IN THE VITREOUS about once in six months, and last about an hour. At the end of attack, patient feels exhausted and goes to sleep. Said to be still during the attacks. Has had five attacks in two years. Has been exceedingly well since the beginning of last summer. N.B. Since writing this report I have seen the patient several times. L.V. was 6/9 on August 8, 1933. She started internal medication and as she began to get better she took ill, and had to stop it. On October 9, 1933, L.V. was 6/12. On October 25, she noted that the L.E. went suddenly worse. On November 2, a detachment of the retina at the lower periphery was evident in the L.E. On November 9, it was seen to be more extensive. Owing to the pathological condition of the L.E., and the useful R. eye, as well as her very unsatisfactory general condition, it has not been considered advisable to operate for the detachment.
Drilling in deepwater is very expensive, with rig rates in the hundreds of thousands of dollars per day and high spread costs.When coupled with drilling exploration wells in areas with unknown and "difficult" formations, the risks escalate exponentially. An example of this is the recent drilling on the ChevronTexaco Upstream Europe discovery well in the West of Shetland province of the UKCS. On this particular wildcat exploration well the potential of encountering a volcanic/basalt sequence had been highlighted at the planning phase. Only limited offset data was available, the closest offset well being some 15 miles (24km) from the proposed well location. A general overview of the well and its objectives is given. The paper focuses on the original drilling philosophy and why it changed during the drilling of the well and the reasons which ultimately led to the use of a turbine and diamond impregnated bit. Factors in the successful drilling of the above well including lessons learnt will be explained. The trade-offs with the various BHA configurations and the impact on data acquisition is also explained. The paper also consolidates the offset information and some of the research and development of basalt drilling at high speeds using turbines.The paper therefore outlines the equipment run in the extensive volcanic/basalt section and the establishing of new benchmarks for the drilling of this extremely challenging formation in a deepwater and high cost environment. Introduction In June 2004 an exploratory well was planned in the Rose Bank area in the West of Shetland province of the UKCS.(Figure 1) The objective of this well was to examine a number of potential Paleocene targets above and below a zone of basalt interbedded with tuffaceous soils. The well was to be drilled vertically in an area where the water depth was 3,658 ft. Drilling the 26" x 36" hole section would be completed using seawater/gel sweeps, followed by the 17 ½" section where a 13–3/8" liner would be installed.Following this, the 12–1/4" section was to be drilled to a total depth (TD) of 12, 258 ft measured depth (MD) using a KCl Polymer water-based mud system to the lower most target where reservoir evaluation could ensue.Contingency plans were to reach TD using 8 ½" hole if there were problems with the 12–1/4" section, such as a poor formation integrity test (FIT) at the 13 3/8" casing shoe, hole instability, etc. Geologically, the top hole sections were to be drilled through soft Tertiary and Eocene formations, consisting predominantly of soft Claystones, Siltstones, and Sands/Sandstones, all with minimal unconfined compressive strength (UCMPS).The 12 ¼" section was predicted to encounter Eocene and Palaeocene sequences of claystones, sands and sandstones, through the Base Cretaceous Unconformity (BCU) to TD. Offset well analysis of these formations using proprietary rock mechanic analysis (RMA) indicated that the majority of the lithologies encountered were less than 3,000 psi UCMPS, with only a few stringers in the basalt zones potentially reaching 9,000 psi UCMPS. The claystone and sandstone sequences below the BCU appeared considerably harder, with average strengths of 7,000 psi UCMPS and occasional stringers reaching 12,000 psi UCMPS. The greatest potential challenge through the 12–1/4" section was the possible presence of up to 820 ft of basalt interbedded with tuffaceous soils in the T45 zone. This basalt could potentially be up to 30,000 psi UCMPS.Offset wells 204/10–01, 213/23–01, and 214/04–01 all showed considerable variation in the basalt thickness and unconfined compressive strength (UCS).However, none of these offset wells were particularly close to the location of the Rosebank well which increased the uncertainty of the geologic predictions.1 Evaluation of drilling basalt in other areas of the world yielded few results. Results that were ascertained varied greatly.This was due to the varying encountered strengths of basalt due to geologic reworking in different areas and under different circumstances.It was concluded, however, that nearly all applications of basalt drilling had been performed with rock bits.
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