Coiled Tubing Drilling Practices at Prudhoe Bay
- G.T. Goodrich (Arco Alaska Inc.) | B.E. Smith (Arco Alaska Inc.) | E.B. Larson (Schlumberger Dowell)
- Document ID
- Society of Petroleum Engineers
- SPE/IADC Drilling Conference, 12-15 March, New Orleans, Louisiana
- Publication Date
- Document Type
- Conference Paper
- 1996. IADC/SPE Drilling Conference
- 1.7 Pressure Management, 1.6.6 Directional Drilling, 2.4.3 Sand/Solids Control, 1.6.2 Technical Limit Drilling, 1.12.1 Measurement While Drilling, 1.6.1 Drilling Operation Management, 1.11 Drilling Fluids and Materials, 1.10 Drilling Equipment, 1.6 Drilling Operations, 1.14 Casing and Cementing, 2.2.2 Perforating, 1.4 Drillstring Design, 5.4.10 Microbial Methods, 3 Production and Well Operations, 1.5 Drill Bits, 2 Well Completion, 5.6.1 Open hole/cased hole log analysis, 1.7.7 Cuttings Transport, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.10 Running and Setting Casing
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Recent drilling experience has led to significant improvements in coiled tubing drilling (CTD) operations at Prudhoe Bay. Since implementation of a full time CTD program in mid 1994, over two dozen open-hole drilling operations have been performed in the Eastern Operating Area (EOA) of the Prudhoe Bay Field. Drilling programs have included simple extensions from pre-set liners to more complex through-tubing horizontal sidetracks. Horizontal sections greater than 1200 feet have been drilled. Measured depths in excess of 13,000 feet have been reached using two inch diameter coiled tubing with 3-3/4 inch bits. This paper will address current CTD techniques used at Prudhoe Bay and compare these techniques with rotary drilling methods.
Coiled tubing drilling techniques have evolved in response to drilling mechanics and hydraulics limitations of coiled tubing workstrings. Bottom hole assemblies (BHA) are designed to improve weight transfer. MWD directional package sensors are located as close to the bit as possible (1 1 to 12 feet) and directional changes are made incrementally to minimize dog leg severity. Less aggressive PDC style bits are used to reduce reactive torque and mud motor stalling. Drill rates of 10 to 20 feet per hour (fph) in shales and 30 to 70 fph in sands are typical. Bit wear is often negligible. Motor life or directional requirements typically limit a bit run.
Weight transfer, hole cleaning, and stuck pipe problems in high departure sections have been reduced through the use of low solids (less than one percent) polymer drilling mud. To improve hole cleaning and prevent cuttings bed build up, rates of penetration are controlled and short trips while circulating are performed frequently. Mud lubricants have improved weight transfer while drilling overbalanced.
Coiled tubing is used extensively in the Prudhoe Bay field for a variety of well service operations. CTD is the latest in a very successful progression of coiled tubing workover applications developed on the North Slope of Alaska. The Prudhoe Bay field has over 1,200 wells with predominantly large tubulars The most common production tubing size is 4- 1/2 inches. There are many excellent opportunities to realize benefits of through-tubing coiled tubing applications with this number of wells having large tubing and strong producing characteristics.
Coiled tubing drilling has become a routine operation in the EOA of the Prudhoe Bay Field. There have been numerous milestones achieved during development of CTD technology at Prudhoe Bay. The most significant accomplishments in development have been configuring the drilling BHA, developing the technique of window milling off of cement whipstock plugs, and developing open hole drilling and completion practices for CTD. This paper focuses on the CTD drilling equipment and open hole drilling practices at Prudhoe Bay EOA.
Rotary rig side-tracking has been a field development main-stay since 1991 at Prudhoe Bay. Producing wells are side-tracked to new bottom-hole locations to access additional reserves and to replace well bores that have developed mechanical problems.
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