Low-density cement used for well cementation

The invention provides low-density cement used for well cementation. The low-density cement comprises the following components in percentages by mass: 5%-8% of high-strength microbeads, 2%-7% of floating beads, 2%-3% of perlite, 55%-70% of oil wells G-grade cement, 8%-12% of silica fume, 3%-9% of fly ash, 2% of a fluid loss agent, 2%-3% of a stabilizer, 1% of an expanding agent, 0.6%-0.75% of an early strength agent, and 0.25%-0.4% of a drag reducer. The low-density cement slurry used for the well cementation provided by the invention has high high-temperature stability, a constant high-pressure density and high early strength, has higher plastic viscosity, dynamic shearing force and thixotropy at high temperature, and is suitable for a well cementing process of high-yield oil wells, gas wells, deep wells, ultra-deep wells, horizontal wells and other wells with higher requirements. 种固井用低密度水泥，其组分和配比按质量分数如下：高强度微珠5％～8％，漂珠2％～7％，珍珠岩2％～3％，油井G级水泥55％～70％，微硅粉8％～12％，粉煤灰3％～9％，降失水剂2％，稳定剂2％～3％，膨胀剂1％，早强剂0.6％～0.75％，减阻剂0.25％