The use of coiled tubing to remove sand from well bores was one of its earliest applications and continues to be an important service today. In fact, sand clean out operations in the Asia Pacific Region still represent some 30% of CT service activity. However, the trend towards more complex well trajectories and reduced topside facilities offshore can impose operational constraints on this essential service.
This paper describes a method of transporting sand out of low-pressure wells, of any angle, using small diameter coiled tubing. It describes the philosophy employed as well as the technical and economic rationale behind that approach. A case study reviews some unique rheological properties of sand suspension fluids and field performance characteristics.
The industry has developed a number of alternative solutions to sand removal, including concentric pipe, wiper trips, jetting techniques and the deployment of large diameter pipe. With the commercial constraints of the service business, depleting reservoir pressures and increasing numbers of high angle wells, the method described supplements the current range of clean out solutions with its elegance, simplicity and logistical merits. This technique involves particle entertainment at the BHA to fluidize the sand and subsequent displacement from the well at low velocities. The main benefit of the system is the avoidance of the need for large diameter, heavy and expensive hardware and the ability to operate in areas where weight restrictions exclude the use of larger equipment.