Set retarding additive for cement composition.

摘要

A graft polymer additive (I) for retarding the set of a hydraulic cement compsn. comprises one or more pendant (co)copolymerised vinyl cpds. (II) grafted onto a backbone sugar of formula A(CHOH)m(D(CHOH)n)pB (III). In (III) A = HOCH2-CR1R2- or HOOC-CR1R2-; B = CR1R2-CH2OH, -C(R1)3, -COOH or -C(R1)2-; D = a gp. of formula (IV), R1 = H, OH and/or CH2OH; R2 = H or O); m and n = 1-3; p = 0 or 1. (II) are selected from 2-acrylamido-2-methylpropane-sulphonic acid (AMPS), vinyl phosphonic acid (VP), vinyl sulphonic acid (VS), acrylic acid (AA), acrylonitrile (AN) and N,N-dimethylacrylamide (DMA). Also claimed is (1) a set-retarded hydraulic cement compsn. comprising a hydraulic cement, sufficient water to form a pumpable slurry, and (I) and (2) a method for cementing a subterranean zone penetrated by a well bore, comprising the steps (sic) of forming a cement compsn. as above.