This paper explains some of the challenges that are faced with coiled tubing (CT) bottom hole assemblies (BHA) when working in high-pressure/extreme-temperature (HP/ET) environments with unfavorable fluids and how these challenges were successfully overcome.

CT was selected as a contingency to operate a downhole completion isolation valve with a hydraulically activated shifting tool and impact tool. By design, this type of valve is operated using a sequence of pressure cycles, working only when a certain differential pressure is present across the valve. CT became the primary option when problems occurred during the pressure cycle operation. After shifting the valve, wireline operations also encountered problems when they hung up prematurely and could not pass a depth in this new HP/ET well with an open hole completion. Initial investigations found that a blockage of swarf combined with settled oil-based mud and calcium carbonate fallout was the source of the problem. Three attempts with two different types of high-pressure/high-temperature (HP/HT)-rated motors ended unsuccessfully after only short exposure to the extreme downhole temperatures.

As an alternative solution, a fluidic oscillation tool was run on the CT in an attempt to clear the blockage. This method resulted in a successful cleanout followed by an acid treatment of the open hole section in a single run with the same BHA.

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