Research and Application of Low-Density Early-Strength Anti-Gas Channeling Cement Slurry for Shallow Offshore Cementing

In response to the challenges of low bottom hole temperature, low formation pressure coefficient, and susceptibility to fluid loss during shallow marine cementing operations, research has been conducted to develop a low-density, early-strength, and gas-migration-resistant cement slurry. Zr-MCM-41 nano-mesoporous molecular sieve with a particle size of 40 ~ 200 nm was synthesized via a hydrothermal synthesis-ion exchange method, serving as a suspending agent that combines low-temperature early-strength performance with suspension stability. Based on close packing theory, slag powder (1 ~ 5 μm) and ultrafine cement (5 ~ 10 μm) were selected as fillers and enhancers. Glass microspheres with a density of 0.44–0.46 g/cm3, compressive resistance of 40 MPa, and fineness D50 of 50 μm were optimized as lightweight materials. Low-temperature early-strength cement was adopted to replace Class G oil well cement, forming a 1.20 ~ 1.50 g/cm3 low-density early-strength anti-channeling cement slurry. The slurry exhibited a static gel transition time is less than or equal to 30 min, fluid loss is less than or equal to 50 mL, and nearly zero free fluid. The cement stone achieved a compressive strength is more than or equal to 7 MPa after 12 h of curing at 38 °C and more than or equal to 14 MPa after 24 h. The density difference of the slurry demonstrated excellent settling stability (≤0.01 g/cm3), and the permeability of the cement stone was less than 0.02 mD. This system has been successfully applied in 5 wells on the offshore platform, with qualified cementing quality.