Cullen drilled two separate boreholes, approximately 4¾ in. The BHA comprised an electric motor and drill collars. outside diameter (OD) and electric-powered cable running internal to the pipe. The Cullen work improved on the original by braiding the hose to carry the “drillstring” weight. Cullen Research came up with an armor-wrapped flexible-string drilling system that used off-the-rack types of motors and drill bits. Cullen in the late 1950s and early 1960s. The flexible-hose Bannister work was followed up by R.H. This initial rigid CTD effort was pioneered by Ben Gray through the drilling of approximately 18 wells over a 14-year period in Canada. by drilling numerous shallow gas wells in Canada. However, it was 25 years before the first actual steel coiled tube drilling found practical application with Flex Tube Ltd. Priestman patent conceived what is today considered modern CTD technology as far as the spooled tubing and operation is concerned. The system was reported to be technically successful but marginally reliable, and development work ceased in 1940 reportedly because of the “lack of a suitable downhole motor” for the new technology. The Bannister work involved using hose for fluid circulation with support cables attached to the sides to carry the weight. Priestman patent application work for the more conventional reeled rigid pipe The following sections will further discuss CTD technologyĭrilling with CT was one of the first ideas for application of continuous workstrings dating back to:ġ926 - the Bannister concept for a flexible hose drillstring 1948 - the G.D. CT is then used to drill a small, clean penetration into the desired zone and is used to run any required completion. In this application, the rotary rig is used to drill a quick and simple wellbore and sets casing just above the desired zone. The most common applications for directionally controlled CTD technology are re-entry drilling/sidetracking from existing wellbores (often through the existing wellbore’s production tubing) and underbalanced, managed-pressure, or low-bottomhole-pressure drilling.Īnother niche market for CTD technology includes the combination of a CTD unit with a low-cost conventional rotary drilling rig. However, even considering the challenges to CTD, there are certain applications in which the unique aspects and capabilities of CTD technology clearly demonstrate that it is the best tool for the job. 1-Purpose-built CTD rig working in Oman (courtesy of Baker Hughes Inteq). Because so much equipment is necessary to handle completion pipe, allow fluid recirculation, and provide for UBD operations, the small footprint and high mobility commonly associated with CT may no longer be a valid assumption.įig. 1 shows a purpose-built CTD rig working in Oman. Numerous truckloads of equipment can take days to rig up in preparation to drill with CT.įig. When including the additional separators and nitrogen-pumping equipment required for underbalanced drilling (UBD), the advantages related to small footprint and high mobility may no longer be the case. These materials are typically not required for conventional CT services. Larger blowout preventer (BOP) stacks, and.Provisions for handling long bottomhole assemblies (BHAs).The complex drilling operations routinely require: However, when more complex CTD services are planned, including directional drilling and cased completions, these advantages may no longer apply. These advantages may exist in situations such as: One example of exaggerated expectations is CTD’s reputation for offering certain advantages, including small footprint, high mobility, and quick operations. Lack of understanding of CTD technology.Reasons for this reputation are numerous and include: There have been numerous highly successful applications of CTD technology in such regions as Alaska and the United Arab Emirates, yet CTD is still considered an immature new technology. 8 CTD tools, techniques, and equipment under developmentĬoiled-tubing drilling (CTD) has a rather extensive history and received a large amount of press and hype from the 1990s to date, a significant amount being less than positive.7 Guidelines for successfully applying CTD technology.5.8 Newer technology with lack of operator experience base.5.6 Reduced pump rates, torque, and WOB.5.5 Logistics of getting equipment to the work location.5.4 Limited equipment and limited experience manpower base.4.7 Potentially fewer service personnel are needed.4.5 Small footprint and greater mobility.4.3 CT provides continuous use of hardwired telemetry and conduits.2 When CTD is the best tool for the job.
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