Extended Reach Drilling with Coiled Tubing: A Case Study on the Alaskan North Slope That Proves the Benefits of Drilling a Straight Hole

A set of five wells were to be drilled with directional coiled tubing drilling (CTD) on the North Slope of Alaska. The particular challenges of these wells were the fact that the desired laterals were targeted to be at least 6,000 ft long, at a shallow depth, almost twice the length of laterals that are regularly drilled at deeper depths. The shallow depth meant that two of the five wells involved a casing exit through three casings, which had never been attempted before. After drilling, the wells were completed with a slotted liner, run on coiled tubing (CT). This required a very smooth and straight wellbore so that the liner could be run as far as the lateral had been drilled. In this paper, we focus on one of the two wells on which triple casing exit was performed. However, the same considerations and results apply to the other wells on which the same technology has been used. Various methods were considered to increase lateral reach, including running an extended reach tool, using a friction reducer, increasing the CT size, and using a drilling bottomhole assembly (BHA) that could drill a very straight well path. All of these options were modeled with tubing forces software, and their relative effectiveness was evaluated. The drilling field results easily exceeded the minimum requirements for success. This project demonstrated record-breaking lateral lengths, a record length of liner run on CT in a single run, and a triple casing exit. The data gained from this project can be used to fine-tune the modeling for future work of a similar nature.