| The gas storage tubular string is a double channel of gas injection and production,and its sealability is always related to the operation safety of the gas storage.The gas storage tubular string is connected by the premium connections,and the premium connections are sealed with their unique metal-metal seal structures.The seal structures of premium connections commonly used are three kinds: cone-cone,cone-arc and column-arc.In order to ensure the operation safety of the gas storage,it is necessary to study the effects of the injection and production process on the performances of the three kinds of premium connections and find out the optimal seal structure type.This thesis mainly carried out the following research works:(1)Based on the analysis of the characteristics of the seal structures,the sealing mechanism and the working conditions of the gas storage tubular string,the main factors influencing the sealability of the gas storage tubular string are found.They mainly contain three categories: the design and processing factors,the construction factors and the working conditions factors.(2)The finite element method was used to study the perfor mances of the three kinds of seal structures and the three kinds of seal structures with defective shoulders under the action of 30 cycles of alternating loads and internal pressure.The results show that the contact pressure curves of the three seal surfaces are arched along their contact surfaces.As the cycle increasing,the maximum contact pressures on the three seal surfaces decrease and the effective seal lengths increase.The contact pressures on the three seal surfaces at gas production are greater than the ones at gas injection,and the distributions of the contact pressures at gas production are wider than the ones at gas injection.When the shoulders of the three kinds of seal structures are defective,the variations of contact pressures and the effective seal lengths are similar to the ones with intact shoulders.Compared to the situations when the shoulders are intact,when the shoulders are defective,the contact pressures on the seal surfaces of the three kinds of seal structures decrease and the contact pressures near the shoulders drop more heavily than the ones far the shoulders.Among them,the variations of cone-cone seal surface are smallest,and the sealability of cone-cone seal surface is most stable.(3)The reliabilities and parameter sensitivities of the three kinds of seal structures are discussed by using PDS technique to find out the optimal seal structure type and put forward the optimization suggestions.The results show that the three kinds of seal structures are both reliable,in which the cone-cone seal structure is optimal.The seal structures should be optimized mainly by expanding the effective seal length,controlling the dimension error,improving the material properties and increasing the make-up torque. |
