To improve the strength degradation of cement sheath at high temperatures during steam flooding or steam stimulation in heavy oil reservoirs,xonotlite whiskers were prepared by hydrothermal synthesis using SiO2 as a silicon source and Ca(OH)2 as a calcium source and applied to oil well ce-ment to inhibit the strength degradation of cement stone at high temperature.The structure and proper-ties of C6S6H whiskers were characterized by TG,FT-IR,XRD,SEM,and EDS.TG analysis showed that the prepared C6S6H whiskers had good thermal stability,and the mass loss at 900℃was only 3.57％.FT-IR and XRD analysis showed that the prepared C6S6H whiskers had complete crystal form and high crystallinity.The morphology of C6S6H whiskers was observed by SEM.The SEM images of C6S6H whiskers were analyzed by image processing software.The length range of C6S6H whiskers was calculated to be 1～16 μm,and the length-diameter ratio range was15～55.The compressive strength test results of cement stone show that the whisker material has a good inhibitory effect on the strength decline of cement stone at high temperatures.The compressive strength of sand-added cement stone is 6.4 MPa when the curing temperature is 280℃,and the decrease rate of compressive strength of ce-ment stone is as high as 78.8％when the curing temperature is 100℃.The compressive strength of sand-added cement stone with C6S6H whiskers was 23.2 MPa at 280℃for 7 days,which was only 48.7％lower than that at 100℃,and the compressive strength of cement paste with C6S6H whiskers remained above 20 MPa after the temperature exceeded 100℃.The compressive strength of sand-add-ed cement stone with C6S6H whiskers was 23.2 MPa at 280℃,which was only 48.7％lower than that at 100℃.The microstructure of cement stone was analyzed by automatic mercury porosimeter and SEM.After the temperature of the sand-added cement stone mixed with C6S6H whiskers exceeds 200℃,C6S6H is distributed in the cement stone with a needle-like network structure with a high aspect ratio,and there is no stacking and hardening of C6S6H in the sand-added cement stone.The pore structure of the cement stone is refined,the compactness of the internal structure of the cement stone is improved,and the high-temperature strength degradation of the cement stone is effectively suppressed.
heavy oil thermal recoveryoil well cementxonotlite whiskermechanical propertyin-tensity decline mechanism
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