Evaluation of Thermal Insulation of Vacuum-Insulated Casing to Prevent Uncontrollable Melting of Ice and Borehole Instability in Permafrost

Abstract

During oil and gas development in permafrost, hot fluids within the wellbore can cause ice melting around wellbore and a decrease in sediment strength, as well as wellbore instability. In the present work, the experimental system for evaluating the insulation effectiveness was established, and the applicability of this experimental system and methodology was verified. It was found that the difference between the experimentally obtained and actual thermal conductivity of the ordinary casings are all within 1.0 W/(m·°C). Meanwhile, the evaluation of insulation effect found that the decrease in fluid temperature, ambient temperature, and vacuum degree can improve its insulation performance. Finally, the numerical simulation was conducted on ice melting and borehole stability during the drilling operation in permafrost. The investigation results demonstrate that the use of vacuum-insulated casings significantly reduces the total heat transferred during the simulation by 86.72% compared to the ordinary casing. The utilization of vacuum-insulated casing reduces the range of ice melting around wellbore to only 16%, which occurs when using ordinary casing. The use of the vacuum-insulated casing resulted in a reduction in the final borehole enlargement rate from 52.1% to 4.2%, and wellbore instability was effectively suppressed.