一种新型超高温固井水泥石抗强度衰退材料

在200 ℃以上超高温下，加砂水泥石强度发生衰退，导致超高温深井固井水泥环层间封隔失效，无法满足高温油气井长期开采的需求。对加砂水泥石的强度衰退机理进行探索，研究发现超高温下加砂水泥水化生成平行疏松的硬硅钙石，孔隙率增大，是其力学性能衰退的根本原因。通过高温水化产物优化设计，优选晶体层间距为纳米尺寸的含铝矿物和纳米管材料，开发了一种新型超高温水泥石抗强度衰退材料DRB-4S。在240 ℃下，DRB-4S加量为10%～20%时，水泥石28 d强度不衰退且大于50 MPa。通过X射线衍射分析、扫描电镜测试、孔结构测试等方法进一步对DRB-4S抗强度衰退机理进行了分析，晶体层间距为纳米尺寸的含铝矿物促进了高温稳定水化产物铝硅钙石的生成，纳米管的加入抑制了雪硅钙石向硬硅钙石转化，并且在水泥石中起到桥联填充作用，降低了水泥石的孔隙率。掺有DRB-4S的固井水泥浆失水量小于50 mL，稠化时间易调，稳定性良好，总体施工性能良好，为高温油气井长期开采提供了有力的技术支持。 

Research on A New Material to Prevent the Strength Decline of Set Cement Under Ultra-High Temperature

In wells with bottomhole temperatures of 200 ℃ or higher, the strength of the set cement with sand will inevitably decrease with time, causing the zonal isolation by the cement sheaths to fail. Wells with this kind of problem will not be able to produce for the designed long time. Researches have been done to investigate the mechanisms of strength retrogression of sanded set cement, showing that the root cause of strength retrogression is the increase in the porosity of the set cement resulted from the generation of parallel loose xonotlite from the hydration of that cement at ultra-high temperatures. To deal with this problem, a new material against strength retrogression of set cement at ultra-high temperatures, DRB-4S, has been developed with optimized aluminum mineral having nanometer crystal layer spacing and nanotube materials. At 240 ℃, a set cement containing 10%–20% DRB-4S has a strength of 50 MPa and does not decrease. Studies on the mechanisms of DRB-4S against strength retrogression of set cement with SEM, XRD and pore structure analysis showed that the use of the nanometer crystal layer spacing aluminum mineral in DRB-4S helps the production of chalcomorphite, a hydration product that is stable at elevated temperatures, in the set cement. The nanotube used in DRB-4S inhibits the conversion of tobermorite to xonotlite and reduces the porosity of the set cement through bridging and filling. Cement slurries treated with DRB-4S have filter loss of less than 50 mL, easy-to-adjust thickening time, good stability and operational performance, all these are of great technical support to the long-term production of high-temperature oil and gas wells.