天然气井试油完井过程中快速泄压对井下工具密封性的影响

压控式井下工具空气室的密封元件不仅受到天然气、二氧化碳、酸碱井液等介质的侵蚀，还要承受井下温度和压力变化带来的影响。在川渝地区天然气井的试油完井中， 压控式井下工具多次出现因“ 气体快速减压（RGD） ”效应影响而造成密封元件的密封性能降低，高压天然气渗入空气室形成了圈闭压力，致使工具不能正常工作的情况。 为了降低RGD效应对试油完井井下工具密封性的影响，以可控封堵阀为例，开展了在井下工况条件下空气室渗入高压天然气的模拟实验，验证特定的井况条件下会产生RGD效应，使橡胶密封元件的密封性能降低；同时通过模拟实验对比，优选了能耐RGD效应的“O”型密封圈，该密封圈在现场应用了4口井，均未出现空气室渗入天然气的现象。天然气的快速泄压对井下工具密封性的影响可以通过控制压降速率、减少开井关井次数和使用耐RGD效应的“O”型密封圈进行防治。为了提高井下工具密封的可靠性，提出了优化设计空气室的密封结构、减小空气室“O”型密封圈承受的密封压差的建议。 该防治天然气快速泄压影响井下工具密封性的技术，为试油完井井下工具的设计和密封件的选择提供了借鉴。

The Influence of Rapid Pressure Relief on Sealing Property of Downhole Tools in the Process of Well Testing and Completion in Natural Gas Wells

The sealing elements of the air chamber of pressure controlled downhole tools are not only eroded by natural gas, carbon dioxide, acid-base well fluid and other media, but also subject to the impact of downhole temperature and pressure changes. During the well testing and completion of natural gas wells in Sichuan Chongqing area, the sealing performance of sealing elements is reduced due to the effect of “ Rapid Gas Decompression ( RGD) ” for many times with pressure controlled downhole tools, and the high pressure natural gas seeps into the air chamber to form a trap pressure, which causes the tools to fail to work normally. In order to reduce the influence of RGD effect on the sealing performance of downhole tools for oil testing and completion, the simulation experiment of air chamber infiltrating into high-pressure natural gas under downhole working conditions is carried out, taking the controllable plugging valve as an example, to verify that RGD effect will occur under specific well conditions, which will reduce the sealing performance of rubber sealing elements; At the same time, through the comparison of simulation experiments, the O sealing ring that can withstand the RGD effect is optimized. The sealing ring has been used in 4 wells on the site, and there is no phenomenon that the air chamber penetrates into the natural gas. The influence of rapid pressure relief of natural gas on the sealing performance of downhole tools can be prevented by controlling the pressure drop rate, reducing the number of well opening and shut in, and using the RGD resistant O-ring. In order to improve the sealing reliability of downhole tools, the suggestions of optimizing the sealing structure of the air chamber and reducing the sealing pressure difference borne by the O-ring of the air chamber were put forward. The technology to prevent the rapid pressure relief of natural gas from affecting the sealing of downhole tools provides a reference for the design of downhole tools for oil testing and completion and the selection of seals.