Patent ID: 9644133
Date: 2017-05-09
CPC Classifications: C04B,C09K,E21B

Claim:
1. A method for maintaining the compressive strength of a well-cementing composition, comprising: (i) providing a cement slurry comprising water, Portland cement, silica and a weighting agent comprising one or more metal sulfates selected from the group consisting of barite, celestine and anglesite, wherein the average particle size of the weighting agent is smaller than 10 μm; and (ii) curing the cement slurry at a temperature higher than or equal to 200° C. and a pressure higher than or equal to 69 MPa, such that the cement slurry sets and forms xonotlite as a main binding phase of a set cement, wherein the one or more metal sulfates are present in at least two median particle-size ranges such that particle packing is optimized, wherein, after 500 hr of curing, xonotlite remains as the main binding phase, and a water permeability of the set cement does not exceed 0.1 mD.