| In order to avoid drilling accidents such as well kick and blowout and ensure safe and efficient exploration and development, reliable well control equipment is necessary in drilling operation. In recent years, with the continuous development of drilling technology, the more and more deep well, ultra deep well and high pressure well make the risk of well blowout in oil field increase. Therefore, how to choose shut well technology to control overflow and prevent blowout becomes particularly important. Currently, hard shut-in, soft shut-in or semi-soft closing are mostly used in well control process in our country. In different closing way, the effect on well head equipment has also varied. Therefore, how to choose the appropriate closing way has become an issue that needs careful research.Aiming at the current situation of well control equipment in a certain oilfield and based on the study of current well control equipment, well control techniques and gas-liquid two-phase flow, water hammer model in hard closing procedure was established and finite element simulation of wellhead pressure changes under different factors and simulation analysis of the ram preventer shell and sealing performance were carried out.In this paper, works was completed as follows:(1) Based on the on-site well control theory and study of well control equipment, the applicable closing way under various objective conditions was analyzed. The conclusion that hard shut-in is more conducive for well control under some certain conditions was drawn. The necessity of analyzing water hammer in hard shut-in was pointed out.(2) On the foundation of gas-liquid two-phase flow analysis, the water hammer wave speed equation and pressure equation were derived under certain assumption. The water hammer model was built and programming.(3) The fluid flow simulations under different working conditions-different opening, different gas content and different velocity-in the process of overflow shut-in were finished by finite element analysis software CFX. Then pressure and velocity variation rules of pipe ram in different situations were obtained so as to provide the basis for follow-up water hammer simulation test.(4) Finite element analysis of the BOP shell under 70 MPa and 105 MPa loads was completed by finite element analysis software ABAQUS. The stress distribution rule and stress concentration area of BOP were found out and safety coefficient is 1.78 which can better meet the security requirements of BOP.(5) Though seal contact stress analysis of rubber head face and drill pipe under 40 MPa, the rubber core combination to be able to achieve the safe seal, which was obtained to provide a reference for theoretical design.(6) Through the contrast of contact stress between the new rubber core and conventional rubber core, the new one could provide a greater contact stress, and thus have a greater sealing pressure to improve capping performance. Because of low coefficient of friction and high wear resistance of PTFE ring, it can reduce the scratch damage and prolong the service life of rubber core.(7) Proposed a hard and soft shut-in experimental program, by comparing the experimental data to determine the feasibility of the hard shut-in way.In summary, research work of this paper provides a theoretical guidance for follow-up water hammer simulation test and a theoretical basis for reliability of well control equipment in hard shut-in procedure on oil field and also of great application value to improve the overall level of well control equipment. |
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