Research And Application Of Ultra-low Density Cement Slurry System

With the exploration and development of complex reservoir such as buried hill reservoirs and marine carbonate fractured reservoir, higher performance of slurry was required, especially in the construction of low pressure drain well, long cementing section and multi-pressure system, where slurry should have good stability, low density, high strength and low shrinkage. Conventional slurry system had been unable to meet the technical requirements, so an ultra-low density cement slurry system with a density of1.10～1.25g/cm3and temperature range of45～75℃was developed.The density of cement slurry system was reduced by lightening material cenosphere DRL-1S which show high pressure resisting capability (14-90MPa), and show obviously effect that density can be reduced to1.10g/cm3when the amount of70%slurry and water floating rate in more than92%, and it reduced the dose lower than55%compared with lightening material3M abroad, and dramatically reduced the cost of ultra-low-density slurry. The system was in an unstable state owning to abundent lightening material, so material DRB-2S with fine granular was added to enhance the stability. The surface area of reinforcements DRB-2S is8000～20000cm2/g and its average particle size is7.58microns, which can not only have condensate rigid reaction but also can be further filled cement paste pore, forming a more dense cement paste, significantly increased the strength and stability of the density slurry. With close packing principle, the deposition rate of ultra-low density cement slurry system was calculated and proportion of enforcement and lightening material was designed. Beads for the skeleton, the use of cement to enhance the filling effect of the material on the beads, which enforce the cenospheres accumulation rate of cement and reinforcing materials, and improve the long-term strength of the cement paste.Fluid loss additive DRF-100S, early strength agent DRA-1S and dispersant DRS-1S were optimized compatibility as admixture material for the ultra-low density cement slurry system. When the dosage of Fluid loss additive DRF-100S is1.8%of cement slurry, the water loss of API is less than100ml, temperature range of30～95℃and added amount range of1.0～2.0%. Thickening time is linear short and thickening behavior with added quantity of early strength agent DRA-1S increasing. Its stability can be enhanced when the added amount is1.5～3.5%. The dosage of dispersant DRS-1S is0.3～0.8%of cement slurry strictly controlled, the stability is worse as added too much.Therefore, the formula of ultra-low density cement slurry system was obtained by experiment of lightening, einforcement and admixture material and evaluted its performance. Experimental results show that:the density difference of cement paste is all less than0.03g/cm3in BP test. The water loss of API is less than100ml. the early strength of cement paste is10MPa/48h in density of1.10g/cm3and12MPa/24h,17MPa/48h in density of1.20g/cm3at55℃. Its long-term strength is24～27MPa and thickening time is180～300min. Field test for the system was proceeded owning to the good evaluation of laboratory experiments. Results show that cementing quality of high3-62-180,3-61-166and3-61-156well are superior quality.