加砂油井水泥石高温力学性能衰退机制研究进展

加砂油井水泥是常用高温固井材料，但在部分高温地层服役时存在短期内水泥石力学性能明显衰退及水泥环层间封隔失效问题，明确其高温力学性能失效机制将有助于合理使用加砂油井水泥。为此，笔者调研了国内外加砂油井水泥高温水化产物和石英砂（掺量、粒径）对加砂水泥石力学性能影响的相关文献，并对其进行了归纳分析。结果表明:加砂油井水泥石在110~210℃温度下服役，可长期保持较好的抗高温性能；在210~300℃静态水环境下，通过调整石英砂级配和掺量可延缓水泥石高温下力学性能的衰退；地层温度超过300℃且处于动态水环境时，由于SiO2大量溶出，加砂油井水泥石难以满足热采井固井质量要求。此外，基于对加砂水泥石硅溶出、水化产物脱钙现象及硬硅钙石晶粒形貌变化的分析，探讨了加砂油井水泥石高温力学性能失效作用机制，并提出了改善其高温力学性能的技术措施。 

Research Progress of Degradation of Mechanical Properties of Sand-Containing Cement in High Temperature Regimes

Sand-containing cement,as the most common cementing material used in high temperature regimes,can encounter problems such as serious degradation of mechanical properties and failure of interval sealing of cement sheath in short time when being applied to high-temperature formations.Hence,the identification of a failure mechanism of mechanical properties under high temperature should facilitate the rational usage of sand-containing cement.By investigating the relevant domestic and overseas documents surrounding the effects of high-temperature hydration products and sand (with factors of quantity and grain size considered) mixed in sand-containing cement on its mechanical properties,it is possible to summarize and analyze the results in a single paper. Results indicated that the sand-containing cement could resist high temperature in a long term under 110-210℃;under the static water environment of 210-300℃,and that this formulation was capable of slowing down the degradation of mechanical properties of cement through adjusting the granular composition of quartz sand.Results also found that under the formation temperature of higher than 300℃ and with a dynamic water environment with a large quantity of SiO2 dissolved out,the sand-containing cement couldn’t meet the quality technical requirements for cementing the targeted thermal production wells.Further,based on the analysis of the phenomena of silicon separated from sand-containing cement and the decalcification of hydration products,along with the variation of morphology of xonotlite crystalline grains,it was possible to analyze and model the failure mechanism of mechanical properties of sand-containing cement under high temperature.At the end,recommendations for technical measures that would improve the properties were proposed and advanced.