- L.J. Leising (Dowell Schlumberger) | K.R. Newman (Dowell Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 1993
- Document Type
- Journal Paper
- 227 - 232
- 1993. Society of Petroleum Engineers
- 1.6 Drilling Operations, 4.4 Measurement and Control, 5.4.6 Thermal Methods, 1.6.6 Directional Drilling, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.1 Drilling Operation Management, 1.14 Casing and Cementing, 4.1.2 Separation and Treating, 1.7.7 Cuttings Transport, 1.6.2 Technical Limit Drilling, 1.10 Drilling Equipment, 4.1.5 Processing Equipment, 1.12.1 Measurement While Drilling, 3 Production and Well Operations, 4.3.4 Scale, 1.11 Drilling Fluids and Materials
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In the 1980's, a "coiled-tubing revolution" began when coiled-tubing services were expanded to include most workover services. In 1991, this revolution expanded to include openhole drilling with a coiled-tubing unit (CTU) in place of a drilling rig. This paper discusses the design process and the limits associated with the use of coiled tubing (CT) to drill new wells and horizontal re-entry wells.
For several years, CT has been used to drill scale and cement in cased wells. Recently, CT has been used (in place of a rotary drilling rig) to drill vertical and horizontal open holes. At this time, <30 openhole CT drilling (CTD) jobs have been performed. However, there is a tremendous interest in this technique in the oil industry; many companies are actively involved in developing CTD technology.
This paper discusses CTD applications and presents an engineering analysis of CTD. This analysis attempts to define the limits of what can and cannot be done with CTD. These limits are calculated with CT and drilling models used for other applications. The basic limits associated with CTD are weight and size, CT force and life, and hydraulic limits. Each limit is discussed separately. For a specific application, each limit must be considered.
Table 1 divides CTD applications into four main categories. First, re-entry drilling in existing wells and new well drilling are considered. Second, vertical and deviated wells are considered. Table 2 is a list of CTD attempts to date that we are aware of. Any errors or omissions from this table are unintentional. Table 2 highlights the applications attempted, CT size, and hole size. It is not surprising that most of these attempts are re-entries because CT services were developed for the workover market. When working in an existing well, there is no need to spud the well or to set surface casing, neither of which can be done with most existing CTU's.
Vertical deepening with a pendular assembly to keep the hole vertical is probably the most straightforward CTD application. A long bottomhole assembly (BHA) is used to provide weight on bit (WOB) without buckling the CT. The neutral point is in the BHA so that the CT is always in tension. Lateral drainhole drilling (Fig. 1) requires milling a window in the casing. A lateral then is drilled through the window with a directional measurement and control system.
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