For a completion where Vacuum Insulated Tubing (VIT) is requested, the thermal performance is one of the key parameters to select the fit for purpose product. The heat loss of a VIT string depends not only on the VIT design, but also on external parameters such as effluent and annular fluid temperature and composition, making it difficult to provide the intrinsic thermal performance of the VIT. The industry doesn't have any codes or standards describing a method to evaluate this thermal performance. This paper presents a comparison of the main thermal test methods used by VIT suppliers and operators and sets the limitations of some of these methods. It also proposes a novel method to evaluate VIT thermal performance.
Most thermal tests are realized either on VIT joints in a workshop or on a VIT completion run in a well. The principle is the use of sensors (i.e. temperature gauge, optical fiber or heat flux meter) to provide information on the temperature gradient that could be linked to the heat losses based on some assumptions on the heat exchange coefficient with the external environment. In the study, these thermal test methods are assessed with a finite elements analysis software, which enables the simulation of the different evaluation methods and their comparison by using the same VIT design.
The study stresses how the details of each thermal test procedure and the assumptions made has an impact on the thermal performance it gives. In particular, the location of the sensors or the fluid considered outside the VIT will provide different thermal performance results when varying. A thermal test method is proposed and assessed with the same software in several simulated environments.
This study shows the difficulties to evaluate the VIT thermal performance on the same basis with different factors that could vary, like the test location (inside, outside or in a well), the sensors location and the test conditions (temperature, external fluid being a gas or a liquid). The study also proposes a new thermal evaluation methodology and assesses it with the same criteria used to analyze the main test methods used in the industry.