Evaluation of Annular Pressure Buildup (APB) during WCD Blowout of Deepwater Hp/Ht Wells

Annulus Pressure Buildup (APB) is one of the major design considerations/problems for deepwater wells. APB is even more problematic in High Pressure/High Temperature (HP/HT) wells. High flow rates could potentially worsen the APB issue. Although conceptually APB is well understood, arriving at an acceptable prediction of its magnitude is challenging and requires a more subtle approach; such an approach would include utilization of appropriate transient multiphase flow and thermal models, in addition to proper handling of the PVT properties of the wellbore and annular fluids. To account for wellbore transient behavior during the Worst Case Discharge (WCD) blowout scenario, a transient multiphase flow model needs to be coupled with a robust transient tubular load/stress analysis model.

To date, there has not been a commercial software package that analyzes the dynamic interaction of fluid flow and tubular systems within a well. Hence, it is proposed herein to employ three independent industry-leading software packages to analyze the 1) fluids, 2) flow, and 3) tubulars, and integrate the outputs into a unified solution.

The proposed new methodology begins with flow dynamics such as pressure and temperature being coupled with the flowing fluid?s PVT properties. Then, the interaction between the fluid?s flowing pressure and temperature and the loads and stresses applied on the tubulars is analyzed. Finally, a Von Mises criterion is used to investigate the wellbore integrity by taking the uniaxial, biaxial and triaxial limits, along with the design safety factors, into account.

Furthermore, the importance of the APB issue in a WCD scenario is highlighted with an example and a remedy, such as an alternative wellbore design.

In the absence of any published literature, guidelines, or software package that could properly analyze the transient effects of the fluid flow and tubular loads, implementation of the proposed new method/procedure could help to predict, identify and resolve potential well integrity issues.