Appropriate Completion To Prevent Potential Damage of Annular Pressure Buildup in Deepwater Wells

Abstract

Abstract Deepwater oil and gas wells will generate annular pressure due to the redistribution of wellbore temperature in production stage when the hyper-thermal fluid is lifted from reservoir formation. Annular pressure threatens casing integrity and well safety. Related accidents have been reported in Mexico Gulf, South China Sea and some other deepwater oilfield. The analysis indicates that annular pressure buildup is so high that deepwater well is in the risk of casing collapse, so it is necessary to take some measures to mitigate annular pressure. Since subsea wellhead is unable to release pressure, appropriate completion measures must be considered. Good understanding of mechanism as well as accurate calculation is prerequisite for appropriate completion, so a model is built based on comprehensive consideration of multi-string interaction and heat transfer process to offer basic pressure data for well completion. According to Annular Pressure Build-up mechanism, pressure can be controlled by releasing expanded liquid out or getting extra space to accommodate liquid as well as slowing down increasing speed of annular liquid temperature. Some completion technologies can work as mitigation measures. These mitigation methods can be divided into two types: active and passive. Active methods function through increasing heat-transfer resistance or eliminating annulus, including full-height cementing, heat-insulated liquid, thermal-insulated pipes and reducing production rate. Passive methods mitigate pressure build-up by releasing some extra space to contain expanded fluid, including cement shortfall, rupture disc, compressible foam and highly compressible annular fluid. These measures differs at cost, operating difficulty, reliability and working mechanism. Among them, thermal-insulated Pipes, heat-insulated liquid, compressible foam, rupture disc, increase the annular liquid compressibility possess good applicability and have been applied in some wells or tested through experiments. Considering deepwater wells' structure, this paper analyzes the feasible measures and offer design methods.