State-of-the-Art Coiled Tubing Technology at Prudhoe Bay, Alaska

Abstract

Abstract Prudhoe Bay, located on the North Slope in Alaska, performs 300 to 400 coiled tubing (CT) interventions per year, employing the latest CT technology. This paper discusses a field trial of CT with an installed fiber-optic line. To date, over 150 CT with fiber optics (FOCT) operations have been successfully performed in BP-owned leases at Prudhoe Bay and Kuparuk in Alaska. Cementing, perforating, fishing, milling, and other wellwork operations were successfully conducted during the two year field trial. The system allows real-time depth, downhole CT pressure, and downhole temperature readings. Real-time temperature can also be measured along the entire length of the CT for distributed temperature surveys. Accurate depth control has been the primary benefit of FOCT at Prudhoe Bay, allowing single trip perforating, plug, and straddle setting. This has resulted in efficiency improvements when adding long perforation intervals, as well as prolonging CT life in the field's abrasive chrome completions. FOCT has become a key enabler for multilateral intervention and an operational case history in a penta-lateral well is described. Introduction Prudhoe Bay, with its long history of innovative CT intervention advances, continues to push the limits of CT technology as its wells become increasingly complex. Daily operations with three 24-hour CT units allow a quick pace for technology development. Multilateral and ultra-extended reach well intervention capability is the primary push for developing new CT technology. It is a well-published fact that wells are being drilled that are deeper, further, and harder to work on than at any other time in history. Although many of these are designed to be "interventionless," history suggests that at some point in the life of the well, intervention will be required. It is critical to develop techniques that can be used in designer wellbores.1 This paper will discuss the field trial at Prudhoe Bay, including a multilateral well intervention case history. Fiber-Optic-Enabled Coiled Tubing One of the most exciting technology developments in recent years is intelligent CT with fiber optics, the marriage of fiber optic technology with CT. The fiber optic line is encapsulated inside a 0.071 in. outer diameter (OD) inconel tube that is pumped through a standard CT reel. Wireline-enabled CT has been available since the 1980's and is still in use in Prudhoe Bay's CT drilling operations. However, it has not been used regularly in Alaska's service CT operations for many years with the advent of memory logging and firing/setting tools, which allow accurate perforating and plug setting. One of the main benefits of LOST is that it does not have the magnitude of "slack wire management" issues that wireline-enabled CT faces. The fiber-optic-enabled CT and a downhole sensor package convey real-time depth, temperature, and pressure at the CT's downhole end. These measurements can be used to make informed decisions with actual data, rather than inferring downhole conditions based on surface data, such as CT pump pressure and wellhead pressure. The system consists of surface electronics, modular toolstrings, and software (Figure 1).