| The new generation well drilling technology is in fast development, which is widely used in various kinds of complex formation. In order to guarantee drilling safety, reduce cost and prevent the well kick、blowout or other accidents, the well control technology must be made as an important part of the study and development. As the key IBOP tool of the drilling string IBOP system, the kelly cock valve is one of the most frequent failure IBOP tools. The performance、lifetime and reliability of the kelly cock valve will directly influence the safety of the workers and property. The optimized design of kelly cock valve based on the failure analysis combined with modes and research status is an effective method to improve the reliability and lifetime, which guarantee the safety of the well drilling simultaneously.Take the φ168kelly cock valve as the research object in this paper, and the main research work embodied in the following respects:(1) The field failure cases of kelly cock valve were counted. The main failure forms were summarized as:the failure by lost strength of valve body, seal failure and rotational failure. The valve body under the pull strength and torsion was analyzed in statics and in Finite Element Simulation; the sealing mechanism and failure causes were analyzed from sealing pressure; the formulas of friction torque between the valve core and the upper seat, and friction torque between rotary knob and body knob holes were inferred。(2) The formula of the flow channel opening of kelly cock valve was inferred? and the major parameters-the close angle of valve core, the radius of valve core and the radius of passageway, which influence the flow channel opening were analyzed, and the variation trends with the parameters aforesaid were discussed. The flow field geometrical models of the kelly cock valve in different flow channel opening were built, and the CFD-Computational Fluid Dynamics Software was used to conduct the numerical simulation. The simulated results indicated that the close angle of valve core and the displacement of drilling pump had the greatest impact on the flow field of kelly cock valve, the solid particle diameter and phase volume fraction had low impact on that. Combined with analysis of major parameters effect flow channel opening and the results of flow field numerical simulation, the relationship between failure and the inner flow field, and the methods of improvement of kelly cock valve were analyzed. Then, the advice in field use was provided.(3) The three-dimensional geometrical modeling of the rotary system (rotary knob, drawing part, valve core and valve seat) was built. The ANSYS Workbench software was used to simulate the stress distribution, deformation distribution and the friction torque between valve core and valve seat of each component of kelly cock valve under different working condition, the rotational moment of valve core. Then, find the weakness parts in the rotating system. The simulation results and the theoretic calculation results of friction torque were contrastively analyzed. The accuracy of calculation formula of the friction torque was verified. (4) Take the weakness parts in the rotating system (rotary knob and drawing part) mentioned in chapter four as optimized object. Through the orthogonal experimental method n half reduction trapezoidal membership function and mathematics comprehensive weighting method. The influence of each design variable on the deformation and stress of the parts was analyzed, and the optimal design scheme was obtained. The structure been optimized has reduced the coefficient of friction between the knob and drawing part with the body, and so the operating torque of cock valve was reduced. |
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