Application of the near equilibrium pressure cementing technique in ultra deep leakage wells: A case study on the Ø168.3 mm liner cementing of Well Wutan 1

Well Wutan 1 is an important wildcat well deployed in the new exploration area of Lower Paleozoic-Sinian in the eastern Sichuan Basin and its total depth is 8 060 m. In the sixth section of this well, Ø190.5 mm bit is used for drilling from 6 600 m to 7 288 m and Ø168.3 mm liner cementing is performed in Gaotai Formation-top of Dengying Formation to isolate the interval of 5 180−7 288 m. In the process of drilling, mud loss happens in Gaotai Formation, Longwangmiao Formation and Canglangpu Formation. The formation’s pressure bearing capacity is only 1.65 g/cm³, the annulus clearance in the overlapped casing section is only 12.69 mm, and friction in the annulus is high, which brings huge challenges to the Ø168.3 mm liner cementing. The anti-channeling toughness slurry system of low density (1.57 g/cm³) and high strength was prepared by optimizing the key materials, such as 3M hollow glass bead and high-temperature reinforcement material DRB-2S, and slurry column structure and construction displacement were optimized to ensure the maximum dynamic equivalent density at the weak point of the wellbore (7 016.3 m) not higher than the formation’s pressure bearing capacity at that point, so as to realize the one-trip upward cementing under the near equilibrium pressure. The application results show that the Ø168.3 mm liner cementing in Well Wutan 1 is of high quality with qualified pressure test result. It is indicated that this method can improve the quality of the liner cementing in the ultra deep thief sections and is beneficial to improve the wellbore conditions for the safe well test of high-pressure gas wells. The research results provide the valuable reference for the cementing of similar leakage wells.