Ø139.7 mm liner cementing technology in the unconsolidated sandstone oil layers of Well Dengtan 1

The primary cementing section of liner cementing of Well Dengtan 1 is 2235 m long, the formation bearing capacity is low, the leakage risk is great, the borehole is large and irregular, and the displacement efficiency can be hardly guaranteed. The open hole is long in the lower oil layer, there are many water layers in the upper part, interlayer breaks are short, and the stabilization difficulty is great. The bonding quality of slurry to unconsolidated sandstone and well wall is poor, and interlayer isolation tends to fail easily. In this paper, the cementing displacement efficiency was improved by increasing the formation bearing capacity, cleaning the borehole, reducing the leakage risk of cementing construction, optimizing the structure of slurry column and adding centralizers reasonably. Oil, gas and water layers were stabilized by using the two-density three-setting slurry system and the annulus pressurization technology. The bonding quality of the second interface was improved by adopting the interface enhanced flushing spacer and the micro-expansion toughness slurry system. The slurry fluidity of micro-expansion toughness slurry system is 22 cm, its thickening time is adjustable within the design range, the filtration loss is less than 50 mL, the free liquid is 0, the settlement stability is 0.01 g/cm³, the expansion rate is larger than 0.4%, the elastic modulus is smaller than 6.0 GPa, and the compression strength of set cement develops quickly to be over 30 MPa after 24 h, which meet the technical requirements of liner cementing of deep exploration well and ensure the quality of Ø139.7 mm liner cementing in Well Dengtan 1. The research results provide a beneficial reference for the following cementing of deep exploration wells in this block.