Cementing practice with abnormal release of liner hanger in Well Lengtan 1 in the Qaidam Basin

After fifth-section Ø190.5 mm bit drills to the depth of 5 708.5 m in Well Lengtan 1, Ø139.7 mm liner is run into the hole. However, it is verified that the liner hanger cannot be released and the risk of cementing failure is aggravated. And meanwhile, the cementing construction is faced with a series of difficulties, such as long primary cementing section of liner (2 506 m), upper-lower temperature difference 65 ℃, strict requirement on the overall performance of cement slurry, serious encroachment of cement slurry into the organic salt drilling fluid, existence of high-pressure gas layer, fast upward flow and hard pressure stability of oil and gas, and high well control risk. In this paper, it was uplifted and rested for 2-3 min by controlling the over pull of 50 kN, 200 kN, 300 kN, 350 kN and 400 kN and then lowered down to the original hang weight of 1 150 kN. And repeated release verification method was performed on each action 3-4 times. In this way, the center pipe was pulled out smoothly and the hanger was eventually released successfully. In addition, the high-temperature anti-gas channeling cement slurry system, the pilot protective drilling fluid and the anti-pollution flushing weighted spacer fluid were adopted to ensure the cementing safety and improve the cementing quality. The high-temperature anti-gas channeling cement slurry system has the mobility higher than 21 cm, the fluid loss less than 50 mL, the free fluid of 0 and the sedimentation stability lower than 0.02 g/cm³. And its thickening time is adjustable in the design range. The compression strength of the set cement develops fast, and the value at the top reaches over 14 MPa after 48 h. In conclusion, it meets the technical requirements of liner cementing in the oil layers of deep exploration wells and ensures the successful construction of Ø139.7 mm liner cementing in Well Lengtan 1.