Thermal Analysis of Subsea Blowout Preventer

Abstract

ABSTRACT A three dimensional finite element analysis was conducted to investigate the temperature distributions of a subsea High Pressure Blowout Preventer (BOP) Assembly and its constituent elastomer seals. The three operating conditions used to simulate the BOP in 40° F sea water were, (1) normal drilling operation, (2) circulation of a kick, (3) flow testing. In order to calculate the temperatures of the elastomer seals, the Newton Raphson method was applied to develop a numerical scheme for computing coordinate mapping and interpreting the corresponding temperatures from the finite element analysis (FEA) solutions. A comparison between the results of a 2D analytical study and the 3D finite element analysis was also presented and both results demonstrated a similar trend of temperature distributions. INTRODUCTION AND FINITE ELEMENT MODEL Up to the present, the blowout preventer, when exposed to well bore at high temperature fluid, was always assembled with high temperature elastomer seals. These high temperature elastomers have a shorter range of useable temperatures than standard temperature elastomers and consequently may cause problems in low temperature environments. Therefore, the purpose of this study was to investigate both elastomer seal temperatures and "Ull" type BOP body temperatures under defined operating conditions. The three operating conditions simulating a 18 ¾"bore, 15,000 psi maximum operating pressure BOP submerged in 40° F water temperature were:(available in full paper) The finite element method was applied to perform this analysis, using the computer program ANSYS [11. The BOP was modeled with three dimensional isoparametric thermal elements. The symmetry feature of the geometry allowed the BOP to be modeled as an % section for Case I and as % section for Cases II and Ill. Several geometric simplifications were also made. The BOP body, intermediate flange and bonnet were modeled as a continuous solid with the same outside profiles as the intermediate flange. The ram change pistons and cylinders were modeled as solid section within the BOP body and bonnet. The finite element models for the cases 1, 11, and Ill are illustrated in the Figures 1, 2, and 3 respectively. The boundary conditions for each case were:(available in full paper) Several additional conditions were assumed for all the three cases:100% thermal conductivity wasassumed between the contacting components of the BOP assembly,Heat loss through end flanges and side outlet flanges were ignored; the hub and flange connections onto the body were eliminated and a general configuration of the cross sectional surface representing the interface of the hub to body was assumed to be insulated,internal surfaces exposed to control fluid were assumed to be insulated. THERMAL AND MATERIAL PROPERTIES The material properties used in this analysis are:(available in full paper)