Numerical simulation of insulated drilling technique with refrigerant fluid in the Arctic region

Abstract

In recent years, there has been a gradual rise in the exploitation of the abundant oil and gas resources in the Arctic. Drilling operations in the permafrost regions of the Arctic can induce thermal energy transfer from the drilling fluid to the permafrost layer, causing permafrost thawing and potentially leading to wellbore instability. Especially when the reservoirs are in deeper formations, the challenge intensifies. In response, some researchers suggest a new drilling technique which adopts the method of injecting refrigerant fluid and vacuum insulated tubing (VIT) cementing for active and passive insulation, respectively. However, due to the novelty of this technique and the complex hydrothermal process in permafrost layers, current studies and numerical models struggle to accurately assess the insulation effect of this method during practical drilling operations. Therefore, referring to previous related research, this article establishes a coupled thermal modeling of this drilling method based on the hydrothermal theory of permafrost. The thermal insulation effect, as well as characteristics of wellbore and formation of this drilling method was investigated through numerical simulation. The findings reveal that compared to conventional drilling methods, this method can effectively delay heat transfer from the wellbore to the permafrost and ensure the volume of thawed permafrost less than 100 m3. Lastly, it is recommended to choose VIT with a thermal conductivity coefficient of less than 0.04 W/(m∙℃), or ensure a flow rate of refrigerant fluid above 7.5 L/s and an injection temperature of refrigerant fluid less than −5 °C when the thermal conductivity of VIT is above 0.04 W/(m∙℃). The model and calculations provided in this paper offer some insights for the implementation of this innovative insulated drilling technique in the Arctic region.