Research On Calculation Method Of Leakage Prediction For Seal Ring In Downhole Equipments

A seal ring is a kind of sealing component which is widely used in downhole equipments. It endures harsh environment with high pressure and high temperature together with the downhole equipments. Besides the harsh environment, seal rings in downhole equipments may sometimes need to undertake special sealing missions. Seal rings with new structure will be required. Based on the conventional experience, it is difficult to make a precise prediction on sealing ability for seal rings in downhole equipments. Leakage amount is a direct index for reflecting sealing ability of seal rings. One can obtain the leakage amount of a seal ring through experimental way. However, it is not only complicated but also wasteful to model the downhole environment on the ground. So it can not be widely used to predict the leakage amount of a seal ring in downhole equipments through experimental way.As computer technology develops, numerical calculation method is well accepted in field of sealing ability analysis. Compared with experimental way, numerical calculation method is cost saving and is able to obtain physical parameters which are not easy got through experimental way. In order to make leakage prediction calculation method for seal ring more common for downhole equipments, the author has done some researches on leakage prediction calculation method for seal ring in downhole equipments based on numerical calculation method.At the beginning of this dissertation, both objective and significance of the task is stated. The review of the research in related fields is given. Present situation of each field is analyzed and further research is proposed. In the end, the research contents of this dissertation is listed.Leakage prediction calculation method for static seal ring in downhole equipments is studied. Framework of the leakage prediction calculation method is presented. Both the functions of each module in the framework and the transmission of parameters are given. Based on fractal theory, a local contacting FE model between static seal ring and matching component is built. A leakage prediction model for static seal ring in downhole equipments is proposed. Realization of the leakage prediction calculation method for static seal ring in downhole equipments is presented on the basis of percolation theory and contacting theory. This leakage prediction calculation method is applied on the static seal rings with different materials, different shapes under different environments. Test is operated to validate the prediction results.Leakage prediction calculation method for dynamic seal ring working in full film lubrication state in downhole equipments is studied. Framework of the leakage prediction calculation method is presented. Both the functions of each module in the framework and the transmission of parameters are given. A leakage prediction model for dynamic seal ring working in full film lubrication state in downhole equipments is proposed. An FE model of the seal ring is built and non-Newtonian fluid interface element is brought in. The fluid-structure coupled problem for dynamic seal ring is solved on the basis of elasto-hydodynamic solution method and FE solution method. Realization of the leakage prediction calculation method for dynamic seal ring working in full film lubrication state in downhole equipments is disployed. Leakage amount of dynamic seal rings with different materials under different environments, different relative velocities is analyzed with the proposed leakage prediction calculation method. The predicted results are verified through experimental way.Leakage prediction calculation method for dynamic seal ring working in mixed lubrication state in downhole equipments is studied. Framework of the leakage prediction calculation method is presented. Both the functions of each module in the framework and the transmission of parameters are given. The concept of nominal dynamic friction coefficient under mixed lubrication state is given. Transient thermal-structure coupled model of the dynamic seal ring is built. Based on meashing technique of finite element method, a mesh reconstruction technique which is used in wear simulation is proposed. Wear simulation method is presented on the basis of this technique. Realization of the leakage prediction calculation method for dynamic seal ring working in mixed lubrication state in downhole equipments is given with IHL method and DHL method. This method is used to predict the leakage amount of dynamic seal rings with different materials under different relative velocities. The results are compared with the experimental results to check whether the proposed leakage method is correct.The leakage prediction calculation methods are used on the seal rings in WLWD device in simulative downhole environment. The fucntion, structure and hydraulic driving scheme of WLWD device are introduced. Take the seal ring near the end of pushing component and the seal ring in the end of the probe componet as examples and predict their leakage amount with corresponding leakage prediction calculation method. The optimal compression rate is suggested for dynamic seal ring. The suggested shape as well as the relationship between leakage amount and compression rate is given for static seal ring. The results are verified through experimental way.