This paper shares the best practices for performing coiled tubing (CT) operations in high-temperature geothermal wells with major challenges such as live well challenges, scaling of pumping fluid, high surface temperatures causing damage to wellhead stack, and CT tag issues. Some geothermal wells have very high bottomhole temperature (BHT) of 550 to 600 °F and surface temperature of 350 to 400 °F, which possess many service quality and health, safety, and the environment risks.

With limited CT geothermal interventions as compared to conventional operations, performing live well CT interventions can be highly risky. Because commonly available pressure control equipment (PCE) seal material is rated to 250°F, the biggest risk is damage to the surface CT equipment, which may result in a well control situation. Generally, the lead time is high, and it is expensive to use temperature seal material rated more than 250°F. A generalized design methodology was developed to check the CT job feasibility in a high-temperature geothermal well. To gain further understanding on the same, three cooling loop designs are compared in this study. Then, the best solution was simulated, implemented, and verified on some wells of "X" field. This design proved to be effective operationally and has reduced the risks for steam inflow into the PCE.

For the case of scaling caused by pumping fluids at high temperatures, this was identified while performing CT operations in geothermal wells of X field. The scale deposited on the CT along with pumping fluid was sent for laboratory hardness and solubility analysis. The results were compared, and lessons learnt to prevent any scaling are discussed. Most of the geothermal wells are completed with a large-diameter completion (7-in., 9.625-in., and higher), which has a bigger flow area to accommodate high steam inflow. Using even a 2.875-in. CT in these wells presents issues of CT tagging at the completion-liner interface, lower annular velocities, and lifting capacity, among others. The best practices were developed on the job to identify the most efficient bottomhole assembly (BHA) design, reducing the probability of CT getting tagged at these depths.

You can access this article if you purchase or spend a download.