Modeling Analysis of Thermally Insulated Fluid to Mitigate Trapped Annular Pressure in Deepwater Wells

Trapped annular pressure is among the primary well integrity risks for deepwater wells, particularly under high-temperature and high-production-rate conditions. The application of thermally insulated fluid to mitigate trapped annular pressure offers the advantages of low cost and convenient operation, yet its applicability still requires systematic evaluation. To investigate the mitigation effect, this paper establishes a model by coupling radial heat transfer between the wellbore and surrounding formations based on annular volume compatibility. The model is mainly composed of two modules: temperature calculation and pressure calculation. A segmented iterative algorithm is adopted to solve the model, which enables quantitative analysis of the variation law under different conditions. Via the proposed model, this paper analyzes the influences of thermal conductivity, production rate, production time and geothermal gradient on trapped annular pressure. The results indicate that thermally insulated fluid can effectively reduce trapped annular pressure, and the mitigation effect becomes more significant as thermal conductivity decreases. Among different injection schemes, the optimal control performance is achieved when thermally insulated fluid is injected into the A annulus. Compared with conventional annular fluids, the B-annular pressure decreases from 50.71 MPa to 21.52 MPa when the thermal conductivity of thermally insulated fluid is reduced to 0.1 W/(m·°C). Thermally insulated fluid still maintains effectiveness under high-temperature and high-production-rate conditions, and its thermal conductivity should preferably be controlled below 0.15 W/(m·°C). Combined thermal insulation measures are recommended for long-term production under high production rate and high temperature. The maximum allowable annular pressure should be determined based on the strength of the C annulus, so as to provide a design criterion for the thermal insulation design.