An Application of Vacuum-Insulation Tubing for Wax Control in an Arctic Environment

Abstract

Summary Several options (prevention and mitigation) for controlling wax deposition inside production wells operating in an Arctic environment are evaluated. Preventive measures include improved heat retention using vacuum-insulated tubing (VIT), active heating using electrical heating elements inside the well tubing, jet pumps using water as a power fluid, and downhole injection of paraffin inhibitors. In the field cases studied, none of these measures is 100% effective in preventing wax deposition. Mitigation methods include mechanical scraping using wireline tools and hot oiling. Again, the mitigation methods are not completely effective, and even a method with 99% effectiveness can damage the well seriously after several jobs. Cost of the wax jobs and the production downtime during the jobs are added losses. The current study showed that an optimal combination of appropriate prevention and mitigation measures is needed for adequate wax control and maximization of economic returns. Extensive field data (production rates and flowing wellhead temperatures) were collected to develop and tune the well thermal model. Laboratory flow-loop data were obtained for wax-deposition scaleup and predictions. The wax-deposition model was tuned to match the field data, including a production-rate decline attributable to wax deposition. An economic model was developed to evaluate the benefits of VIT with appropriate polyurethane coupling insulation in achieving higher production rates and lower production downtime during the wax jobs vs. the capital expense of the VIT segment. The results showed that it is highly beneficial to run the VIT, at least in the permafrost layer. Additional length of VIT below the permafrost layer has limited benefits.