Coil tubing is a single string of pipe, which can intervene into wells and perform specific jobs without mobilizing a rig. The basic applications are cleaning wellbore/perforations, stimulating selective zones, controlling wells, milling/drilling cement/tools/fish downhole, conveying tools in deviated/horizontal wells, gas lifting, setting cement plugs below production packer, and many other applications.

Operating coiled tubing units in HPHT and ultra HPHT wells requires conformance of specific parameters for safety and successful operations. Challenges of the operations and treatment design are exacerbated considering the environment downhole. The conditions become more severe in ultra HPHT environment if the well is deviated or approaches horizontal.

Intervention and treatment in ultra HPHT and in highly deviated or in horizontal wells requires special procedures, techniques and tools. The requirements include modified procedures as well as equipment and products to withstand the BHST temperatures for the entire operation.

As an example of complications in HPHT wells, on the east coast of India, bottomhole static temperatures could go as high as 507°F and mud weight could vary between 14 and 19 ppg in deviated wells. Experience has shown that conventionally calculated bottomhole circulating temperature alone is inadequate to determine the working temperature downhole. However, with the help of computer-aided temperature simulation and all the above techniques, many successful CTU operations have been executed under these difficult conditions.

Using case histories for illustration, this paper will share best practices developed from 4 years of successful interventions in HPHT and ultra-HPHT wells. These practices will include HPHT coil tubing intervention considerations, modified procedures, special techniques and product choices.

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