Modeling of Subsea BOP Shear and Sealing Ability Under Flowing Conditions

Abstract

A computational modeling effort was undertaken to combine finite element analysis (FEA) and computational fluid dynamics (CFD) methods to simulate the closing of the blind shear rams of a blowout preventer (BOP) under flowing conditions. The objective of this effort was to develop a high-fidelity fluid-structure interaction (FSI) simulation methodology that reliably assesses the combined mechanical and hydrodynamic forces acting on BOP shear rams that could potentially impact the rams’ ability to safely shut-in a well. BOP shear ram designers typically consider the material properties and geometry of the drill pipe to be sheared and the hydrostatic flowing pressure during ram closure. Fluid hydrodynamic effects on the rams are difficult to simulate and currently cannot be produced in a laboratory setting due to complexity and personnel safety in conducting such tests under high transient conditions, and thus are often neglected. To determine the best computational approach in terms of complexity and accuracy, a novel simulation methodology was developed by coupling the fluid interaction with the BOP as it shears a drill pipe using LS-DYNA® and ANSYS® Fluent®. The conditions and assumptions made for this analysis are presented herein, and initial simulation cases are compared against validation data to confirm model accuracy. For a high-pressure, high-flow well scenario in the Gulf of Mexico (GOM), a one-way coupling of the FEA and CFD simulations was determined to be the best approach for modeling the closing of blind shear rams under flowing conditions. This investigation also confirms that as long as the fluid is single phase, the ram forces due to fluid flow effects are small in comparison to the mechanical shearing force. It is noted, that highly dynamic flow events such as slugging flow or the potential erosive effects of sands or solid particles present additional risks, and the analysis methodology described here can serve as the basis for additional investigations into more complicated flow scenarios.

Test-Free Simulation Method for Blowout Preventer Pipe Shearing Powered by Data

“…Previous publications [7,9,10] of BOP shearing simulations have reported the errors in the range of 5.8% to 18.7%. This work chose the error tolerance as 15% and successfully found a parameter function.…”

Metamodeling of structural failure: Case study of API S-135 steel tube cut in BOP

“…Hitherto, there has been no systematic study for API S-135 steel failure characterization. Although FEM simulations provided results coherent with experimental observations, the pipe cut mechanism is not completely understood, as indicated in [31]. In order to deepen the understanding of all BOP process of cutting the drill string, the material failure behavior must be better analyzed, in a likely stress state range.…”

“…More recently, Liu et al [30] reproduced the work from [28], by using the failure model proposed in [29] calibrated by a micromechanical approach (Figure 17). In 2018, McCleney et al [31] also modeled the pipe cut of a BOP under flowing conditions using the Johnson-Cook material model, simulating a well shut in in a blowout condition concluding that it does not interfere relevantly in the cutting process. Castilho, in 2016, compared the ultimate force obtained from numerical and analytical models.…”