The Experiment Study Of Floating Pearl & Micro Silica Low Density Cement Slurry

With the increasing development of oil field exploitation and the technical advancement in drilling and production, particularly along with the more and more extended exploration depth, the continuous scale-up of deep or ultradeep wells, complex wells, long-isolation sections and absorption wells, allows the conventional cement systems beyond the cementing needs. It plays a significant role for low-density cement slurries to prevent oil and gas formations from contamination and enhance the overall cementing quality. Abundant survey and study of extensive literatures demonstrate that appropriate experimental optimization on the concentrations of cement, floating pearl and micro silica, a low-density cement slurry system can be obtained, which can remarkably decrease the permeability and improve the strength of set cement with widely-ranged density.Results obtained from experimental study show that the optimum dispersant concentration ranges from 1.2% to1.5%. The fluid loss of the low-density cement slurry can be reduced to satisfy the requirements of the cement system merely when the concentration of the fluid loss additive reaches more than 1.5%. Comparison of the compressive and bending strength of set cement for different formulations and curing time, the use of early-strength agent ranging from 1.2% to1.8% can significantly improve the early-strength of set cement. The final formulation is obtained as follows: ShengWei class-G cement + floating pearl (20~50%)+micro silica(13~23%)+ fluid loss additive(1.5~2.0%)+dispersant(1.2~1.5%)+early-strength additive (1.2~1.8%), and the cement/water ratio is 0.44. According to this formulation scope, the created lightweight cement system possesses good regulation in density width, improved stability and flow property, definite thixotropic property, lower fluid loss and higher early-strength. The system can remarkably improve the cementing quality and effectively inhibit the oil- and gas-bearing formations from leaking and damaging in cementation.