高温条件下G级油井水泥原浆及加砂水泥的水化和硬化

利用X射线衍射仪和扫描电子显微镜研究了80～240℃温度范围内温度、硅砂对G级油井水泥水化硬化的影响,检测和分析了硬化体的水化产物、微观结构和强度,揭示了水化产物组成、微观结构及硬化体抗压强度的变化特点.结果表明:当养护温度超过110℃时,不添加硅砂的水泥原浆的主要水化产物由CSH(Ⅱ),C2SH2,C3S2H3转变为C2SH,硬化体微观结构由三维网络状结构转变为板快状或团块状结构,原浆水泥石抗压强度随温度升高而降低;在相对较高的温度条件下,添加硅砂的水泥主要水化产物则分别转变为C5S6H5,C6S6H(>150℃),C5S5A0.5H5.5,C3.2S2H0.8及其他类型的水化硅酸钙晶体,硬化体的微观结构相应地变为纤维网状、粗框架、短平行针状及团块状,在温度为100～150℃范围时,添加硅砂的水泥硬化体抗压强度随温度升高而增加,而在温度为150～240℃范围时.抗压强度随温度升高而降低.对于温度超过120℃的深井,合理的硅砂加量为30%～40%.

HYDRATION AND HARDENING OF CLASS G OILWELL CEMENT WITH AND WITHOUT SILICA SANDS UNDER HIGH TEMPERATURES

The effects of temperature and silica sands on the hydration and hardening of Class G oilwell cement were studied for a temperature range of 80-240 ℃ by using X-ray diffraction and scanning electron microscopy. The hydration products, microstructure and compressive strength of the hardening cement paste were tested and analyzed. The varying characteristics of composition and microstructure of hydration products and compressive strength of hardened paste were revealed. The major products of a clean cement slurry (without silica sands) changes from CSH( Ⅱ ), C2SH2, C3S2H3 to dicalcium silicate hydrate (C2SH) when the temperature exceeds 110 ℃, while the microstructure of hardened paste changes from a three-dimensional fiber network to a blank-block or mass block for different curing temperature eonditiuns. Also, the compressive strength of the hardened paste decreases with the increase of curing temperature. The major products of cement slurry with silica sands changes into C5S6H5, C6S6H(>150 ℃), C5S5A0.5H5.5, C3.2S2H0.8 or other kinds of calcium silicate hydrate at high curing temperatures, while the microstructures are transformed into a fiber network, rough frame network, short-parallel-needle fiber or mass block structure. The compressive strength increases with the increase of temperature in the range of 100-150 ℃, but it decreases with the increase of temperature in the range of 150-240 ℃. For oilwell temperature exceeding 120 ℃, the optimal amount of silica sands to add to cement slurry to enhance the strength of hardened paste is determined to be 30%-40%.