川西地区须家河组气藏深井固井的难点及对策

Cementing difficulties and solutions in the Xujiahe Formation gas reservoirs,west Sichuan Basin

川西地区上三叠统须家河组气藏具有埋藏深,目的层断层多,地层破碎,泥页岩易坍塌掉块,同一裸眼井段压力系数差别大(须五段至须三段地层压力系数接近2.0,目的层须二段地层的压力系数为1.5左右),天然气显示活跃且气层多,固井防气窜难度大等固井难点。针对上述问题,提出了安全固井的对策:①对于易漏失地层的固井,可采用连续正注反挤固井作业;②对于长裸眼井段固井,如果地层承压能力不能满足单级注水泥,可采用多级注水泥方式,在条件允许的情况下可用双胶塞注水泥;③对于表层大尺寸套管固井,采用内插管固井;④对于油气层尾管固井,尽量采用旋转尾管固井,优化设计水泥浆性能,以达到替净井内钻井液进而提高固井质量的目的。

Cementing in the upper Triassic Xujiahe Formation gas reservoirs in the western Sichuan Basin is facing up to many challenges of great burial depth,too many faults at payzones,broken beds,caving shales,a big pressure difference existed in the same open hole section (e.g.,formation pressure coefficient close to 2.0 from Xu 3 to Xu 5,about 1.5 in the target zone of Xu 2),active gas show,multiple gas zones,and potential gas channeling trends.Effective measures for the above-mentioned difficulties are recommended here as follows:1) for cementing in thief formations,continuous circulation through both drill string and annulus should be proposed;2) for cementing in long open holes,if the formation can not afford the pressure of single stage cementing,multi-stage cementing should be adopted,and double-plug cementing ought to be adopted also if possible,3) for large-size surface casing cementing,stinger cementing should be used,and 4) for liner cementing at reservoirs,rotating cementing technique and optimal slurry systems should be adopted to displace completely the drilling fluid downhole so as to improve the cementing quality.