Diversion Analysis And Structural Improvement Of Rotary BOP Shell

Rotating blowout preventer (RBOP)is the key equipment of gas drilling wellhead safety control system, used for packer wellbore annulus and drill string, providing safe and effective pressure control during drilling operation, and also transporting the high-speed cutting particles in the wellbore to the wellhead quickly. During the gas drilling, the high velocity returned fluid contains a large amount of drill cuttings particles, it will repeatedly impact and scour the inner wall of the shell when it go through the shell of RBOP. And resulting in the shell body and bypass port erosion failure, what’s worse, it may cause the shell pierced or rapture, leading to the wellhead can not shut down properly, and serious accidents like blowout. Therefore, the diversion performance and anti-erosion ability of RBOP directly determines the efficiency and reliability of the chip.Aiming at the problem of erosion of RBOP during diversion process in gas drilling, accesses to the domestic and foreign research present situation of structure of RBOP and erosion mechanism, surveys the erosion characteristics of drilling and wellhead equipment. This paper uses combining methods of theory analysis and numerical calculation to study the internal flow characteristics and the law of debris particle distribution and erosion in the XK-I and the XK-Ⅱ RBOP. Then based on XK-Ⅱ RBOP (shell side outlet:diameter182mm one-way diversion), carried out the structure of flow field of shell, to improve the diversion performance and anti-erosion ability of the shell. The main research work are as follows:(1) Analyzed the working principle of RBOP in gas drilling, studied of the main erosion failure reasons of RBOP shell, established the erosion equations RBOP shell;(2) According to the internal medium flow characteristics of RBOP shell, established the ROP shell gas-solid two-phase flow numerical model by using the theory of turbulence and multiphase flow theory;(3) Built three-dimensional flow field models, which are different ways of diversion and drill pipes (or pipe joints) went through the rubber of two kinds of RBOP. Conducted the numerical simulation of gas-solid two-phase flow of internal shell, obtained law of Loop air flow characteristics, debris particles distribution, and erosion of shell in different conditions (fast/slow drilling).(4) Based on XK-Ⅱ RBOP (shell side outlet:diameter182mm one-way diversion), carried out the sensitivity analysis of shell side outlet chamfer in the fast drilling, obtained the rules of chamfer radius effects on casing annular flow field and got the optimal chamfer. Then proposed a new rubber that can improve the ability of diversion and anti-erosion.The method and conclusions of this paper can provides s a new way to improve the efficiency and reliability of RBOP shell. This research has a certain reference value to the RBOP shell structure design on the high life, high performance.