A Study Of Cement Hydration Mechanism In Deep Wells

In cement hydration process, with the temperature rising, reaction period and hydration period was ahead. The induction period shortens and hydration reaction time decreases. With the temperature increasing, there are two critical temperature point where cement strength recesses, namely 110℃and 150℃.The recession will accelerate and the starting recession point head with the temperature increasing. Sand cement strength has a two level or jumping growth at a certain temperature scope. Determining a reasonable amount of silica sand within the range of 20% to 50%. The more silica, the better intensity development and anti- intensity recession.Within 80~100℃, cement silicate hydrates are C2SH2,CSH(Ⅱ),C3S2H3, which has net shape and good performance. While above 100℃, cement form low intensity and permeability C2SH which causes cement strength recession. C2SH will increase dramatically if the temperature is above 150℃. Adding silica sand to cement whose temperature ranges from 110～150℃or maintaining it in 110℃about three days, cement can form the fiber C5S6H5. After temperature above 150℃, it form thick needle C6S6H which can to some extent effectively curb the high-temperature recession of cement strength.We have understand that the thickening time and the application level of retardant have do with its molecular structure. So when considering the construction site slurry formulation design, full consideration should be given to high temperature stability of the selected retardant and the impact process of cement hydration and cement strength and compatibility to get a reasonable amount. In addition, we have also appraisaled relations between thickening time cuvre and glue strength .The results have provided basis and foundation for the deep well system and formulation which use G-class cement as basic material. It plays a guiding role in completion. For the temperature at 80～200℃, It gives preliminary design of cement system. The year 2005, we have tested the temperature-resistance cement slurry at several sites of the daqing oil flied. It effectively satisfies five wells construction and guaranties the five wells completion quality. By the end of 2006, the temperature-resistance cement slurry has used successfully in the Daqing deeper gas field, Daqing external deep horizon, Daqing deep Inclined wells, horizontal wells. It achieves better results in completion.