Development and Corrosion Inhibition Mechanisms of a Corrosion Inhibitor for Self-Diverting Acids
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摘要: 低渗碳酸盐岩酸压成功的关键在于酸压后形成可在地层闭合压力下保持高导流能力的酸蚀裂缝。单相缓速酸是一种具有纳米结构、低伤害、低摩阻及高缓速性能的新型酸液体系，应用潜力大，但其酸蚀裂缝导流规律尚不明确。以光滑岩板和粗糙岩板为实验对象，以盐酸、胶凝酸和乳化酸为对比，利用酸液刻蚀和酸蚀裂缝导流实验、表面形貌扫描和连续强度测试仪，研究了酸液类型、交替注入级数、注入速度、黏度比、反应时间、岩板类型对导流能力的影响。结果表明：单相缓速酸相对于盐酸、胶凝酸和乳化酸，可形成强沟道型刻蚀形貌，差异化溶蚀程度高，岩板强度损伤减缓，在高闭合压力下可保持较高的导流能力。提高酸液交替注入级数（≥3级）、注入速度、黏度比（黏度差≥50 mPa·s）及岩板初始表面粗糙度，有助于形成优势酸液流通通道。单相缓速酸实现高导流酸蚀裂缝机理为：①黏性指进形成差异化刻蚀沟道；②主蚓孔滤失形态及“虹吸”效应减缓裂缝表面强度损伤。Abstract: Self-converting acids are widely used in the acid fracturing of carbonate reservoirs. Conventional corrosion inhibitors used in self-converting acids have, because of the unique molecular structure of the viscoelastic surfactants (VES), poor compatibility with other components, thereby drastically reducing their corrosion inhibitive performance. In this study, two pyridine quaternary ammonium salt corrosion inhibitors, SI-1 and SI-2, are synthesized with 1-chloromethylnaphthalene, 4-ethyl pyridine, benzyl chloride and 2, 3-cyclopentenopyridine. Using corrosion tester and rheometer, the corrosion inhibitive performance of SI-1 and SI-2 in self-diverting acids is studied. Also studied are the effects of SI-1 and SI-2 on the viscosity of the diverting acids. Using SEM, EDS, atomic force microscope and X-ray photoelectron spectroscopy, the surface morphology and chemical components of the steel plates before and after corrosion are analyzed from a microscopic point of view. The corrosion inhibition mechanisms of SI-1 and SI-2 are investigated using molecular dynamic simulation method. The results of these studies show that the two pyridine quaternary ammonium corrosion inhibitors have good corrosion inhibitive performance in self-converting acids and they only very slightly affect the viscosity of the self-converting acids being studied. The two corrosion inhibitors have wide applicability and are cost-effective. Compared with SI-1, SI-2 is a better corrosion inhibitor. At 90 °C, the corrosion rate of the steel plates in 1% corrosion inhibitor is 1.04 g/(m2∙h), at 120 °C, the corrosion rate is 7.43 g/(m2∙h), the final viscosity of the VES residual acids is 190 mPa∙s or higher, and the operation cost can be reduced by 20%. When adding 1% corrosion inhibitor SI-1 or SI-2 into the self-convert acid, no apparent corrosion can be found on the surface of the steel plates, and the Fe content is greatly increased, indicating a significant reduction in surface roughness. When SI-2 is used, the Fe content is increased from 86% to 94%, and the Ra value reduced from 137 nm to 84 nm. In both cases, C-N and carbonyl C=O are detected on the surface of the steel plates, indicating the existence of adsorption membranes formed thereon by the corrosion inhibitors. Molecular dynamic simulation results show that SI-2 has small energy gaps and big adsorption energy, and when the SI-2 molecules are adsorbed on the surface of the metal, a dense adsorption membrane is generated, isolating the contact between the corrosion media and the surfaces of the steel, hence remarkably inhibiting the corrosion of the steel. The application of SI-2 in the Bohai oilfield and the Iraq Missan oilfield has been very successful.
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表 2 酸液体系性能参数
体系 体系配方 η/mPa·s
（170 s−1，25 ℃）缓速率/
%界面张力（25 ℃）/
mN·m−1电导率/
mS·cm−1摩擦阻力/
%粒径/
nm盐酸 20%HCl 1.6 31.1 100 100 单相缓速酸 20%HCl+5%
单相微乳液2.1 92.6 0.003 98.8 25（加0.1
减阻剂）8～100(粒
径中值约为20 nm)稠化酸 20%HCl+
0.8%稠化剂48.7 71.3 30.2 100 30% 乳化酸 酸物质的量浓度相同 56.6 96.8 0（油包水乳液） 0 150 >1000 
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表 3 酸蚀裂缝导流能力测试实验方案
实验变量 岩板编号 交替注入
酸压液体注入级数 泵速/
mL·min-1t/
min总液量/
mL总时长/
min酸液类型 DL-1/DL-1C 变黏滑溜水 3 100 10 6000 60 单相缓速酸 3 100 10 DL-2/DL-2C 变黏滑溜水 3 100 10 6000 60 盐酸 3 100 10 DL-3/DL-3C 变黏滑溜水 3 100 10 6000 60 乳化酸 3 100 10 DL-4/DL-4C 变黏滑溜水 3 100 10 6000 60 胶凝酸 3 100 10
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表 4 光滑岩板酸蚀表面定量化描述
变量 编号 形式 接触比/% 面迂曲度 迂曲倾角 峰谷差/% 峰谷差方差 刻蚀体积/cm3 酸液体系 单相缓速酸 DL-1 沟槽 10.1 1.087 4.74 4.92 0.0350 58.38 盐酸 DL-2 沟槽 18.9 1.157 6.78 11.08 0.0558 124.57 乳化酸 DL-3 均匀 23.3 1.038 0.17 0.20 0.0055 13.07 胶凝酸 DL-4 均匀 21.3 1.044 0.59 0.22 0.0002 36.18 注入
级数一级交替 DL-5 均匀 17.4 1.046 1.17 2.44 0.0090 69.18 二级交替 DL-6 沟槽 24.3 1.058 1.90 3.67 0.0137 68.51 四级交替 DL-7 沟槽 14.7 1.155 4.59 4.51 0.0267 63.98 黏度
比低黏度比 DL-10 均匀 34.7 1.055 0.70 0.90 0.0018 57.99 高黏度比 DL-11 沟槽 15.1 1.111 5.28 4.98 0.1573 68.99 注入速度 低注速 DL-12 沟槽 21.0 1.088 3.16 2.89 0.0217 49.14 中注速 DL-13 沟槽 25.3 1.077 3.22 3.55 0.0218 57.07 反应时间 30 min DL-14 沟槽 13.5 1.058 1.98 2.59 0.0165 29.00 90 min DL-15 沟槽 30.1 1.165 6.39 9.06 0.1532 103.95
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