Lance Portman

Reducing the Cost of Coiled Tubing Cleanouts by Conducting Them Without Nitrogen

One of the most common applications of coiled tubing is the removal of sand or other debris from wells. The typical operation involves circulating fluids down the coiled tubing and up the well. The fluids are designed to carry the sand from the bottom of the well to surface, without killing or over pressurizing the well. Because most sand producing wells are under pressurized, gas is typically required to keep the hydrostatic weight of the return fluid column under that which the reservoir can support. This gas is typically nitrogen. Difficulties arise in many locations around the world where the supply of nitrogen is problematic, or at least very expensive. A cleanout method that does not require nitrogen removes the need for a timely, reliable and cheap source of nitrogen as well as the need for cryogenic pumps and tanks. This paper details the use of concentric coiled tubing and a down hole jet pump to conduct cleanouts in the balanced or underbalanced condition without the use of nitrogen. This technique has been the subject of previous papers, demonstrating its applicability in difficult, deviated well profiles. This paper describes the enhancements made to the system to make it suitable to simple wells, focusing on lowcost, lower-tech operations as opposed to difficult applications. The first case histories are included.

The Science and Economics behind Coiled Tubing String Design and Optimization

Coiled tubing has made great advances in recent years, increasing in size, strength and reliability. This lias lead to a great increase in services that can be run on coiled tubing and in turn has lead to bigger, more complex and more expensive coil equipment being built and offered to the market With all this new equipment now on the market, it becomes more difficult to select the most appropriate equipment for a particular job, or indeed for a project of work that involves many different types of operations. There is a tendency to assume that biggest is best. Both commercially and technically, the big coil unit may not always be the best choice. This paper gives examples of the current capabilities of coiled tubing units, dispelling some of the myths associated with the smaller units such as You cannot drill with a small coil unit or You always need a big coil unit in order to gel higher circulation rates. The paper also lists applications where big coil units absolutely should not be used. Finally, guidelines arc set out based on general technical and economic performance comparisons between varying size coil units. Several techniques are listed which permit smaller coil sizes to be used in place of bigger units. Tlie paper uses examples from actual field work and computer simulations.