一种能有效防止水泥浆回流的新型套管胶塞

A new type of casing plugs effectively preventing the backflow of cement slurry

为了进一步降低尾管固井后水泥浆回流到套管内的风险,研究了目前国内外主流尾管悬挂器的防回流结构,分析该类工具结构存在的缺点,进而开发设计了一种新型结构的套管胶塞——半空心套管胶塞,并对其与悬挂器的配合使用进行了现场试验。结果表明:(1)尾管悬挂器防回流结构的缺点是钻杆胶塞的锁定机构在到达套管胶塞与之重合和锁定前已被损坏;(2)新型胶塞的内孔设计为弯折孔,上半部分为空心圆孔,下半部为实心圆柱;(3)固井施工时,钻杆胶塞到达悬挂器位置后进入新型胶塞内,在孔弯折处被阻挡,不能继续下行,与套管胶塞成为一体;(4)在钻井液推动下剪断剪钉继续下行,经套管串达到碰压座位置,新型胶塞下部实心圆柱体挤入碰压座内孔,只需要套管胶塞上的密封件和锁止机构一起作用即可防止水泥浆回流,而不再需要钻杆胶塞;(5)现场试验应用表明,试验井的实钻水泥塞面平均比设计高出24 m,较对比井高出设计位置59 m减少了一半。结论认为,新型胶塞与悬挂器匹配良好,对施工过程没有负面影响,固井后水泥塞面控制效果良好。

For mitigating the hazards of slurry flowing back into the casing after liner cementing, the deficiency of slurry backflow pre-vention structure of current liner hangers at home and aboard was analyzed in this paper. Then, a structurally new casing plug, i.e., a semi-hollow casing plug was designed and developed. And it, combined with the hanger, was tested on site. And the following research results were obtained. First, the deficiency of the slurry backflow prevention structure of liner hanger, is that the locking mechanism on the drill pipe plug is damaged before it reaches the casing plug and matches with each other. Second, the inner bore of the semi-hollow casing plug is designed as a bend hole, which has a hollow round hole in its upper part and a solid column in its lower part. Third, during the cementing operation, the drill pipe plug enters into the semi-hollow casing plug once it gets to the position of hanger. And it is stuck at the bend and cannot go down anymore. Consequently it is integrated with the casing plug as a whole part. Fourth, when the shear pin goes down to the setting seat through the casing string under the force of drilling fluid, the solid column at the lower part of the semi-hol-low casing plug is squeezed into the inner hole of the seat. In this situation, the backflow of cement slurry can be prevented only by using sealing elements and locking device on the casing plug instead of by using drill pipe plug. Fifth, field tests show that the cement top of test wells is only 24 m higher than the designed value while that of offset wells is 59 m higher. Obviously, the former is 50% less than the latter. In conclusion, this newly developed semi-hollow casing plug matches well with hangers, having no negative effects on cementing operation, so the cement top after cementing can be well controlled.