Modeling and Simulation of Annular Pressure Buildup APB in a Deepwater Wellbore with Vacuum-Insulated Tubing

摘要

Annular pressure buildup (APB) is a major concern in high pressure, high temperature (HP/HT) well design. High temperature hydrocarbon production increases wellbore temperature significantly, inducing a large APB as a result of annular fluid thermal expansion. Vacuum-insulated tubing (VIT) can be used to reduce the annulus temperature increase to mitigate APB. However, because of the natural differences between VIT and standard pipe, there is uncertainty about accurately modeling the VIT wellbore temperature distribution and its effect on APB. The VIT vacuum section has much better insulation than the connector, which induces a nonuniform heat transfer that generates significant annulus temperature spikes along the axial direction, up to 50°F in half- VIT unit length (20 ft) (Gosch et al. 2004). Conventionally, the axial temperature gradient is ignored because it is negligible in comparison with radial temperature gradients. This assumption is no longer applicable with VIT because these temperature spikes significantly enhance natural convection. This study presents a novel wellbore heat transfer model that considers nonuniform heat transfer and enhanced annulus natural convection to provide accurate VIT well temperature predictions and APB estimates.