三高条件对弹韧性水泥浆性能的影响及短期腐蚀机理

Study on the Influence of Elastic Toughness Cement Slurry Performance and Short-term Corrosion Mechanism under HPHTHS Conditions

针对固井水泥石所处的高温高压含H_(2)S/CO_(2)腐蚀环境以及复杂工况,开展三高条件下弹韧性水泥浆的性能变化及短期腐蚀机理研究。基于弹韧性外掺料的3种主要类型,采用向G级油井水泥中分别加入10%橡胶粉末、0.3%玄武岩纤维以及10%丁苯胶乳的方式制备弹性水泥浆。通过力学性能测试、XRD、FTIR、MIP及SEM-EDS测试,分析弹韧性材料添加前后及腐蚀前后,水泥石的力学性能、孔径分布、水化产物类型及微观结构变化。结果表明,掺入3种弹韧性材料均有利于水泥石的脆度系数降低、韧性提高,其中玄武岩纤维最利于控制材料破坏时裂缝的发展,而丁苯胶乳最利于降低材料的弹性模量和保持较大的抗折强度。经过短期液相腐蚀后,水泥试样的力学强度均出现增长,特别是掺入玄武岩纤维和丁苯胶乳的试样。玄武岩纤维在该研究中的腐蚀条件下性能稳定,腐蚀反应生成的致密碳酸钙晶体堆积于玄武岩纤维与水泥基质界面孔隙处,引起了腐蚀后材料总孔容的减小及力学强度的大幅度增长。丁苯胶乳在水泥石中形成聚合物膜,覆盖及包裹水泥基质,可提高复合水泥表面的耐腐蚀性能。

To understand the corrosion environment of a set cement at high temperature,high pressure and high H_(2)S/CO_(2) conditions and the complex work condition thus formed,a series of experiments were conducted to study the property change and short-term corrosion mechanisms of elastic tough cement slurries under the“three-high”conditions.A class G cement slurry was treated with three main elastic tough additives commonly used,i.e.,rubber powder at 10%,basalt fiber at 0.3%and styrene-butadiene latex at 10%.The cement slurry thus formulated was rendered elasticity to some extent.Using several methods such as mechanical property measurement,XRD,FTIR,MIP and SEM-EDS etc.,changes were studied in the mechanical properties,distribution of pore throat sizes,types of hydration products and micro-structures before and after the cement slurry was treated with the three additives and was cured under corrosion conditions.The measurement results show that the addition of the three elastic tough additives is beneficial to the decrease of the brittleness and to the increase of the toughness of the set cement.Among these additives,the basalt fiber is the best additive for controlling the fracture development in the set cement when it fails,and the styrene-butadiene latex is the best additive for reducing the elastic modulus and maintaining a high flexural strength of the set cement.After undergoing a short-term corrosion in liquid environment,the mechanical strengths of the cement samples were all improved,especially the set cement containing basalt fiber and styrene-butadiene latex.Basalt fiber under the corrosion conditions showed stable properties,the dense calcium carbonate crystals produced in the corrosion process were piled in the pores located at the interfaces between the basalt fiber and the cement matrix,leading to a decrease in the total pore volume in the corroded set cement and a substantial increase in the mechanical strength of the set cement.The styrene-butadiene latex can form a polymer membrane inside the set cement,which covers and wraps up the cement matrix,thereby improving the anti-corrosion property of the cement surfaces.