Technical Difficulties and Countermeasures of Liner Cementing for Well KS-X’s Horizontal Section of Target Stratum

Well KS-X is the first horizontal well in Kuqa Piedmont with a depth of 7200 m. The Φ127.00 mm liner casing was used to seal the target stratum in the final section, the length of the primary sealing section and horizontal section was 1150 m and 400 m respectively. During this drilling period, frequent lost circulation occurred with active oil and gas, and the safety density window was narrow, so it was difficult to stabilize and prevent leakage in cementing process. The cementing quality is difficult to guarantee due to the problems such as insufficient casing center degree in the horizontal section, difficulty in improving the displacement efficiency, high temperature and high pressure (HTHP), and the absence of electrometric diameter. Considering the above technical difficulties, the following key countermeasures are formulated. To ensure the smooth entry of casing, the preparation of the borehole and the optimization of the performance of the drilling fluid are necessary before cementing. The entry scheme of one casing with one centralizer was obtained by software simulation, which could realize the casing center degree generally greater than 40%. The cementing leakage pressure was determined to be 1.49 g/cm3 based on the analysis of the engineering geological conditions. The maximum displacement was determined to be 1.1 m3/min based on the parameter design, which not only ensures the displacement efficiency, but also reduces the risk of leakage. Low friction spacer fluid, low-density lead slurry and conventional density tail slurry with anti-invasion and anti-channeling effect were used in cementing process. It not only stabilizes the formation and prevents gas channeling, but also forms a suitable friction gradient difference to ensure displacement efficiency and interface cementation quality. Increasing the amount of spacer fluid from 20 to 28 m3 could significantly improve the risk of annular retention of drilling fluid. By increasing the amount of the lead slurry and improving the upper plug sealing length, the cement slurry fill rate can be increased to over 95% throughout the wellbore. By decreasing the sealing height of the tail slurry can prevent the risk of the slurry from rising to the bell nipple due to the absence of electrometric diameter. After cementing, good waiting measures should be taken to prevent the risk of gas channeling caused by tail slurry weight loss. As a result, the cementing operation was smooth, the qualified rate of cementing quality was 91.1%, the pressure of oil test was 46. 26 MPa, and the daily gas production was 150,000 m3. This represents a breakthrough in cementing technology for horizontal wells in the Kuqa Piedmont and lays the technical foundation to support ultra-deep horizontal wells in the future.