Tubular restrictions from scale buildup can significantly reduce hydrocarbon production, subsequently reducing the production capacity of a well. Before production can be restored, this buildup must be removed. Although scale buildup is a global problem, the material composition and characteristics of scales can vary drastically, even within the same field. As a result, most tools traditionally used for scale removal cannot efficiently remove scale inall well conditions. This paper discusses a recently developed, customized jetcleaning tool that addresses the problems inherent with scale-cleaning operations.
Scale removal can be difficult because many removal methods cannot control jetdwell time, which is the time required
to accomplish scale removal based on the type and hardness of the scale. Because jet dwell time increases with the hardness of the buildup material, cleaning efficiency is measured by the capability of the scale-removal method to control dwell time. Traditional jet cleaning tools have not provided adequate control, which has severely impacted their operational performance. Anew, slow-rotating jet cleaning tool helps minimize jet dwell time without introducing repetitive cyclic effects on a coiled tubing (CT) workstring.
The slow-rotating jet cleaning tool can also be used for cutting tubulars. Previously, tubulars could only be cut by mechanical, explosive, or chemical methods. CT was used either to deploy positive-displacement motors (PDM's) for rotating mechanical cutters, or to deploy pressure-activated firing devices that initiated the firing sequence in explosive or chemical cutters.
This paper discusses the evolution of CT cleaning procedures, alternatives to cleaning with CT, and the design and application of the new slow-rotating jetcleaning tool. Case histories discuss the use of the jet cleaning tool for removing scale and production buildup on tubing walls. The new tool can be used for performing through-tubing cuts, and can help reduce service costs for difficult applications, such as those involving long bottomhole assemblies. The capacity of the newjet cleaning tool to control jet dwell time and pumpabrasive fluids helps reduce the risks, obstacles, and costs associated with traditional cutting and cleaning methods.
Scale deposits on tubing walls and perforations can stop well production, inhibit the injection of well fluids, and cause downhole production equipment to become lodged. If left untreated, these problems are compounded, and hydrocarbon production will continue to decrease.
Early Use of CT for Cleaning. The choice of a scale-removal treatment is often affected by cost because treatment methods such as acidizing or milling with small-diameter tubing can be expensive. The introduction of CT in the 1970's provided a lower-cost option for scale removal because CT operations could be performed under live well conditions, reducing down time.
CT provided a washing action for removing scale buildup materials. Acids run through the tubing chemically reacted with the scale, extracting waste materials from the tubing and restoring the flow path of the fluid to the basepipe.