适用于稠油热采井热膨胀水泥的外掺料优选

Optimization of Admixture for Thermal Expansion Cement Used for Cementing Heavy Oil Thermal Recovery Well

对于稠油开发来说,开采温度可以达到300℃,剧烈的温度增加会造成水泥石强度的衰退,同时高温条件下套管、水泥环膨胀变形不一致,会导致水泥环内部产生过大的应力,这些都是造成水泥环密封完整性被破坏的主要原因。除了解决水泥石高温强度衰退问题之外,加入不同的外掺料改善水泥石的热膨胀性能是保证密封完整性的主要措施之一。热膨胀系数是其热膨胀性能的主要表征参数,为此研究了各种外掺料在不同温度下对油井水泥石热膨胀系数的影响,并分析探讨了其影响机理。实验结果表明:硅粉和漂珠等外掺料会不同程度地降低硬化水泥石的热膨胀系数,而胶乳和碳质材料的掺入可以适当增大油井水泥石的热膨胀系数。这种碳质材料为工业废料,价格低廉,因此在油井水泥中掺入适量的碳质材料不仅节约固井成本,还可以提高水泥石的热膨胀性能,保证水泥环的密封完整性,提高热采井的生产寿命。

In heavy oil thermal recovery, the high temperatures, 300 %, for instance, will deteriorate the strengths of set cement, and generate over high interior pressure inside the cement sheath because of the difference between the swelling capacities of the casing string and cement sheath. The strength deterioration and the over high interior pressure are the main factors contributing to damage to the integrity of the airtightness of the cement sheath. Several methods can be used to maintain the airtightness of the cement sheath, for example, controlling the strength deterioration of the set cement at elevated temperatures, or adding admixtures to the thermal expansion cement to improve the expansion behavior. Factors affecting the coefficient of thermal expansion of a set cement, the main parameter characterizing the thermal expansion behavior of the set cement, have been studied by adding various admixtures into cement slurries at different temperatures. Mechanisms of these factors affecting the coefficient of thermal expansion have also been investigated. It was found that some admixtures, such as silica powder and hollow micro spheres, reduce the coefficient of thermal expansion of set cement to varying degrees, while other admixtures, such as latex and carbonaceous materials can increase the coefficient of thermal expansion of set cement. Carbonaceous materials, as industrial waste, are cheap and their use in oil well cement not only reduces the cost of well cementing, but also improves the thermal expansion behavior and the airtightness of set cement, thereby prolonging the lifespan of a thermal recovery well.