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Coiled Tubing |
In the oil and gas industry, the term Coiled Tubing (CT) refers to a very long metal tube, typically 1 to 3.25 inches in diameter, that is supplied in a large coil.
The length of coiled tubing varies depending on the diameter and application and can range from 2,000 to over 15,000 feet (approximately 600 to over 4,500 meters), with record lengths of over 30,000 feet (more than 9,000 meters) for special applications. The total length depends on the capacity of the coil gauge and the size of the pipe diameter.
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It is used for interventions in oil and gas wells and sometimes for the production tubing in depleted gas wells. Coil tubing is often used for similar operations to wireline. The main advantages over wireline are the ability to pump chemicals through the coil and force them down the wellbore, rather than relying on gravity. Pumping can be quite self-contained, almost a closed system, because the tubing is continuous instead of bolted.
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In offshore operations, the footprint for a coil tubing operation is generally larger than for a wireline solution, which can limit the number of rigs where coil tubing can be performed and make the operation more costly. Typically, a coil tubing operation is performed by the drilling rig on the oil platform, which is used to support surface equipment. However, a cantilever rig can also be used on drilling rigs. Onshore, they can be operated with smaller service rigs, and mobile, self-contained coil tubing can be used for lighter applications.
The tool chain at the bottom of the coil is often referred to as the Bottom Hole Assembly (BHA). This can range from simple nozzles such as spray nozzles for pumping chemicals or cement through the coil tubing to a larger array of logging tools, depending on the operations.
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Coil tubing has also been used as a cheaper version of workover operations. It is used for drilling and milling open wells. It can also be used for reservoir fracturing, a process in which fluid is pressurized at a specific point in a well to fracture the rock and allow product flow. Coil tubing, when used correctly, can perform virtually all oil well operations.
Reference(s)
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Remark(s) of the Author...
Additional information
After publishing this article, a good friend sent me a link to the Dutch NAM (Nederlandse Aardolie Maatschappij), an innovative company that supplies energy to society and industry. NAM also uses coiled tubing, and below is a short translated summary of their activities with coiled tubing.
In older natural gas fields, contaminants can occur in the well. These can include salt, but also sand. This can cause the well to become clogged. NAM cleans such wells by pumping water through a flexible metal tube. This allows the gas to flow freely upward. This technique is called coiled tubing cleanout.
Gas production also brings other substances to the surface, such as water and sand. Water contains salt. This salt can settle at the bottom of older wells. Sand can also clog the holes in the sandstone layer containing the gas. In both cases, the gas can no longer flow freely. In that case, we have to flush the well.
Flushing
Flushing gas wells is usually done with water, sometimes with a mixture of liquids. If there is
salt in the well, it dissolves in the liquid. The sand in the well, originating from the gas-bearing
sandstone, is flushed upwards as well.
Preventing Waste
NAM also uses coiled tubing cleanout for other types of contamination. For example, to clean the
rock containing the gas. In that case, we first inject hydrochloric acid into the rock. The acid
removes all contaminants. Then, we remove the reacted acid from the well using coiled tubing cleanout
and nitrogen. We also use coiled tubing cleanout when bringing new wells into production. These
are still full of water or brine. We pump this water or brine out using coiled tubing cleanout
and nitrogen.
I hope this short article about NAM and Coiled Tubing can give you an impression of what else is possible with Coiled Tubing.
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