Modular Marine BOP Stack

ABSTRACT The Modular Blowout Preventer (BOP) stack integrates, in a compact way, the main components of an underwater BOP assembly. In this approach the annular BOP, the ram BOP's and the wellhead connector are locked together using four hydraulically pretensioned stud bolts that extend the full height of the stack, outboard of the BOP bodies. The development of modern, large bore, high pressure control equipment has brought with it greater efficiency for the marine drilling industry. But, these larger assemblies are also taller in their conventional form. Eliminating the individual connections between the stack components in the modular concept has resulted in a substantial savings in overall height. This compact BOP architecture is possible because of side ram exit allowing easy packer change in tight spaces. Also, by using four large bolts to preload the entire BOP and connector assembly, the ability of the modular stack structure to carry high bending and pressure induced loads has been greatly enhanced, (also confirmed in a finite element analysis of the complete assembly). Four large stud bolts extended through two circular termination plates located on top around the annular BOP and the wellhead connector below. These plates or reaction rings, transmit the bolts loads that are developed during a bolt tensioning process, compressively preloading all stack components. Metal-to-metal sealing between the stack components is accomplished at this time as well. All four studs are simultaneously preloaded during initial assembly using detachable hydraulic tensioners. The net result is a rigid and compact stack assembly that will safely handle large bending moments and pressure applied loads.