Abstract

In the oil industry, there is always a need to go deeper and cheaper. Coiled tubing's greatest advantage is being able to operate without a rig, cutting costs and time by a great extent. To this day, coiled tubing has been used for many well services like cementing, stimulation, cleanouts, drilling, production, perforation etc. As this technology gains fame and takes the place of the jointed string, the need for its versatility also increases. Coiled tubing is highly used in horizontal wells for its flexibility. Unfortunately, due to its small size, there are higher chances of tubing getting locked up in the process of intervention. To extend its reach, a number of tools and techniques like friction reducers, tapering tubing, tractors etc. have been invented and been used. However, these tools and techniques can only be used on a case by case basis.

This paper introduces buoyancy reduction, one other technique to extend the reach of coiled tubing in horizontal wells. The concept behind this technique is to reduce the net weight of the tubing by creating a buoyancy effect. This is done by pumping a very light fluid into the tubing while intervention to create a large difference in the densities of the annular and the tubular fluids. The higher density of the annular fluid creates a buoyancy effect on the tubing and thus reduces the drag against the well floor. Moreover, the low density fluid also increases the rigidity of the tubing and makes it follow a transverse wave pattern, similar to that of a free flowing garden hose. Both the lower weight and the transversal wave motion of the tubing help it to wriggle its way into the well. In this case, simulations showed an extended reach of 23%.

Each well may need a different technique for extended reach. As per the requirement of the case, a combination of these technologies can be used to reach the planned measured depth. Buoyancy reduction is one other technology that is available for use that is easily implementable at minimal added cost.

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