Cement Slurry System for the Long Open Hole Section of High-Pressure High-Temperature Deep Wells in the Sichuan Basin

The depth of natural gas wells in the Sichuan Basin ranges from 5500 m to 7500 m, the temperature of the target layer ranges from 140 °C to 160 °C, the pressure coefficient of the layer is 2.05~2.35, and the length of the open hole section is 2800 m to 4000m. The complex formation with multiple production layers and multiple leakage layers results in many challenges for well construction engineering. During cementing of a deep well, the challenges include high temperature and pressure, gas migration and leakage, and "ultra-retardation" at the top of the cement column when a cement slurry is used to address the problem oflong-interval isolation. To solve the complex technical problems encountered during cementing, a multi-function cement slurry system was developed for long-interval isolation at temperatures between 70 °C and 160 °C. The maximum compressive strength of the cement slurry at the top of the cement column with 4000m length was reached after 48 h and the cement slurry exhibited good leak-proof and anti-gas channeling performance. After mechanical modification, Young's modulus of the cement paste was lower than that of the conventional cement slurry (less than 6.0GPa) and the tensile strength of the cement paste was 30% higher, exhibiting an improvement in the damage resistance of the cement sheath. The cement slurry system was successfully applied to more than 100 high-temperature high-pressure wells in the Sichuan Basin, reaching maximum values of 7793 m well depth, 3954 m length of the liner cementing section, 100 °C temperature difference, and 2.40 g/cm3 cement slurry density.