A Novel Thixotropic Well Cementing Slurry

Mature thixotropic cement slurries are seldom seen in China presently. Slurries commonly used in oilfelds are of weak thixotropy, temperature sensitive, and have poor overall properties. To solve these problems, a thixotropic agent, N-1, has recently been developed by combining a synthesized amphoteric polymer and an inorganic nano material. The amphoteric polymer has high widely distributed molecular weight (MW, about 6.0×10⁶). At room temperatures, the high MW polymer molecules dissolve very slowly, and the dissolution becomes fast as temperature rises. This feature ensures the amphoteric polymer. The inorganic nano material selected is a fbrous material, which forms a network in water through adsorption and entanglement. N-1 was characterized for its microstructure, and was used as main additive to formulate a novel thixotropic cement slurry. Laboratory evaluation indicated that the cement slurry had strong thixotropy and did not lose without the action of pressure. At a pressure of 2.1 MPa, a cement slurry treated with 1.0%N-1 to 1.5%N-1 had volume of loss from 380 mL down to 0 mL. At elevated temperatures, the thixotropy of the N-1 treated cement was enhanced, instead of weakened, and had low flter loss (40 mL) and high strength (aged at 62℃ for 24 hours, the strength was 31.6 MPa.) Compared with conventional cement slurries, this cement slurry has strong thixotropy and good overall properties, and can satisfy the needs of well cementing.