Performance Test and Numerical Simulation Research on Vacuum Insulated Casings for Permafrost Protection

Because permafrost settles as it thaws, there is a risk that the wellhead will sink while drilling, and therefore, vacuum insulated casings were introduced to protect the permafrost, and their thermal insulation performance was analyzed through experiments and numerical simulations. The field test results showed that the vacuum insulated casings could limit both the radial and the axial heat transfer on the surface simultaneously, which restricts the range and magnitude of temperature increase on the casing surface. Because the vacuum insulated casings have much lower apparent thermal conductivity than that of traditional casings, their thermal insulation performance can be maintained at various ambient temperatures and drilling fluid temperatures. In addition, decreasing the vacuum degree can improve their thermal insulation performance and strengthen their protection of the permafrost. The numerical simulation results indicated that the vacuum insulated casings could greatly reduce the permafrost thaw zone and lower the possibility of settling and wellhead sinking due to permafrost thaw. Furthermore, the following measures were adopted to enhance the thermal insulation performance of the vacuum insulated casings, including vacuum degree reduction, insulated casings length increase in the casing assembly, and insulation foam wrapping at the coupling. The research results have verified the effectiveness and stability of vacuum insulated casings in protecting the permafrost, so as to guide the development of oil and gas resources in the Arctic region.