Study and Application of an Ultra-Low-Density Cement Slurry

To successfully cement wells penetrating low-pressure easy-to-leak formations in Ebei (north Hubei) area, Zhongyuan Well Cementing Company has developed a high strength ultra-low-density cement slurry suitable for use at temperatures between 60℃ and 120℃. The cement slurry was formulated with self-developed light-weight cement, high strength hollow glass beads (as light-weight material) and ultra-fine silica powder. With this three-level grading model, an ultra-low-density design framework was established. The performance of the ultra-low-density cement slurry was optimized with AMPS filter loss reducer, low-density strength enhancer, early-strength agent and retarder. The cement slurry had density of 1.15 g/cm³, filtration rate of 40-42 mL, free water of less than 1.0%, density difference of 0, and adjustable thickening time below 300 min. The thickening curve was right-angled. At atmospheric pressure and 40℃, the set cement had 72 h compressive strength of 12.1 MPa, which satisfies the needs of field operation. Staged mixing procedure was adopted in mixing the cement slurry. 98% of the bulk slurry samples had properties very close to the properties of the slurry samples made in laboratory, indicating that the cement slurry had stable properties. In cementing the well D12-P42, well D17-2 and well DK13-FP1 in Daniu block (north Hubei) with the ultra-low-density cement slurry, no loss of cement slurry happened, and pass rate of the cementing job quality was 100%, realizing the borehole integrity expected. The successful application of the ultralowdensity cement slurry has provided a technical support to cementing wells penetrating low-pressure easy-to-leak formations.