A级水泥环的胀缩性能

为了解A级水泥石在井下的胀缩规律,利用水泥环应变测量系统对A级水泥在不同养护条件及不同硬度地层条件下的胀缩性进行了测量.结果表明:①环境的渗透性对水泥的胀缩及强度有影响,在水渗透的条件下,A级水泥的线性膨胀率大,界面强度高;在非水渗透环境下,水泥石的线性膨胀率小,界面强度低;②水泥环收缩是以水泥环的几何中心为中心进行收缩的,因此,水泥收缩在一、二界面都有可能产生微环.水泥膨胀是朝着抵抗力小的方向发展,由于井下有泥饼存在,所以水泥膨胀一般首先朝向地层的方向发展,因此用膨胀水泥可提高二界面的封固效果;③不同硬度的模拟地层,对一界面的胶结强度影响很大.地层越软,水泥对一界面的胶结强度越低;地层越硬,水泥对一界面的胶结强度越高.

Expansibility and contractibility of Class A cement sheath

To find the expanding and constructing law of Class A cement sheath down hole, expansibility and contractibility of the cement at different hardness and in different aging conditions were measured by strain testing. Results are as follows: 1) the permeability of the surrounding formation influence the expansibility, contractibility and the strength of the cement. If water exists, the linear expansion rate is high and the interface strength value is small. 2) as the contraction of the sheath is processed taking the geometric center of the sheath as its center, in both interfaces, microsheath probably produces; as the cement expansion processes in the direction of resistivity decreasing, and resistance of mud cake adhering to the hole wall exists, the cement sheath expands in the direction to the formation. From this fact, expansive cement could be used to improve cementing quality of the interfaces. 3) hardness of the simulating formation has great influence on the consolidation strength of the first interface, that is, the softer the rock is, the lower the strength of the interface exists, and the harder the rock is, the higher the cement strength produces.