Practice of liner cementing facing both well kick and lost circulation in Well Shi-70 of Qaidam Basin

In Well Shi-70, drilling of the liner wellbore section encounters both the high-pressure brine layer and thief zone. The drilling fluid cannot balance the high-pressure aquifer. Meanwhile, internal circulation is present downhole and disturbs the annular pressure system. Consequently, cementing is prone to lost circulation, high difficulties are found in sealing the high-pressure brine layer, and cementing quality is associated with high uncertainty. Based on cement slurry performance tests and cementing practice analysis, the high-temperature-tolerant high-density thief-zone-plugging cement slurry system was designed. The system has a density of 1.88–2.40 g/cm³, with the stability below 0.03 g/cm³, SPN less than 3, adjustable thickening time, and 24 h comprehensive strength of above 18 MPa. The casing/linear injection-annulus squeeze method was adopted in field practices. The required thickening time was estimated from the operation parameters. By reducing the thickening time of the tail slurry and lowering the pump rate in the later stage of slurry displacement, the slurry was gradual thickened and set during the low-rate displacement to rapidly seal off the high-pressure aquifer. Then, cement squeeze through the annulus was performed to seal off intervals above the thief zone. Thus, the Ø273.05 mm liner cementing was successfully completed in this well. The cementing quality at the casing shoe and thief zone was tested to be premium and that at the brine aquifer was also acceptable. The practice provides successful experience for liner cementing in this area.