What Coiled Tubing Is

Coiled tubing (CT) is one long, continuous steel pipe that is stored on a large reel. It has no threaded joints along its length. A single string can be several thousand metres long. The crew unrolls it from the reel, guides it over an arch, and pushes it down into a well. When the job is finished, the crew pulls it out and winds it back onto the reel.

Most coiled tubing used in well services has an outside diameter between about 1 inch and 2-7/8 inches. Larger sizes exist for special work. The steel is strong but thin, so the tubing can bend around the reel and then straighten again as it goes into the well.

Three things that make coiled tubing useful

• It works on a live well. The well can stay under pressure. A sealing device called the stripper closes around the moving tubing, and a blowout preventer (BOP) stands ready below it. The crew does not need to kill the well first.
• It can pump while it moves. Because the tubing is a pipe, fluid or nitrogen can be pumped down it at any time — while running in, while stopped, and while pulling out.
• It is fast. There are no connections to make up or break out. The tubing runs in and out continuously, so a trip takes far less time than with jointed pipe.

A simple picture of a coiled tubing job

Imagine a gas well in a desert field. Sand from the reservoir has filled the bottom of the well and covered the perforations. Production has fallen. A coiled tubing unit arrives on several trucks. The crew installs the pressure control equipment on top of the Christmas tree. They run the tubing into the live well with a jetting nozzle on the end. They pump water and nitrogen down the tubing. The fluid lifts the sand up the annulus — the space between the coiled tubing and the well's production tubing — and out to a tank at surface. When the sand is gone, the crew pulls out, rigs down, and the well goes back on production.