Coiled Tubing Drilling Practices at Prudhoe Bay

Abstract

Abstract 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 (11 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.