普光气田高含硫气井带压更换采气树工艺技术

采气树在使用过程中如出现腐蚀、泄露、机械故障等而又无法在线修复的情况,则需要进行整体更换。但像四川盆地普光气田这样孔、洞、缝较发育的酸性碳酸盐岩气藏,若采用先压井再整体换装采气树的方法会造成储层的二次污染,很难再恢复到修井前的气井产能。为此,考虑作业安全和生产实际,研究形成了"两封堵一隔离"带压更换采气树工艺:①安装地面泄压放喷流程,进行整体更换采气树演练,准确测算所需的时间;②关闭井下安全阀,通过泄压放喷管线排放井下安全阀以上通道内气体,进入放喷池点火燃烧,将井口油管压力泄至0;③连接液氮泵车按照测算量向井筒顶替液氮;④安装双向背压阀,利用送取工具,将背压阀安装在油管悬挂器内的背压阀座面,封堵油管;⑤整体更换采气树,试压合格后按照操作规程取出双向背压阀。现场成功应用2口井,很好地解决了高含硫气井不压井更换采气树的技术和安全控制难题。

A technology in replacing Christmas tree under pressure for high sour gas wells in the Puguang Gas Field,Sichuan Basin

A Christmas tree can be hardly repaired on line and is always in need of integral replacement due to corrosion, leakage and mechanical failures in the service period. Generally, the entire Christmas tree has to be replaced after well killing. However, well killing is easy to cause secondary pollution in reservoirs, especially in the carbonate gas reservoirs with well-developed pores, holes and fractures in the Puguang Gas Field, Sichuan Basin, so the productivity of a gas well becomes difficult to restore to the productivity level before well workover. Therefore, in view of the work safety and actual production in this field, a new technology was developed to replace the Christmas tree under pressure through twice plugging and once isolation. The technology was specifically described as follows: (1) to install a ground relief blowout pipe, conduct the exercises of integral replacement of the Christmas tree, and accurately estimate the required time; (2) to turn off the downhole safety valve and discharge the gas in the channel above the safety valve through the relief blowout pipe into a flare pit, then ignite the gas, and reduce the pressure of a wellhead oil pipe to 0; (3) to connect a liquid nitrogen pump truck, and replace liquid nitrogen in well bore according to the calculated results; (4) to install a two-way back pressure valve: use a tripping tool to mount the back pressure valve on a back pressure valve seat in a tubing hanger, and seal the tubing; (5) to replace the whole Christmas tree and remove the two-way back pressure valve according to operating procedures after a pressure test. The technology was successfully applied in two gas wells on site and resolved the technical difficulties in the Christmas tree replacement and safety control without well killing.