Luo Zhifeng, Zhang Nanlin, Zhao Liqiang, Wu Lin, Liu Pingli, Ren Dengfeng, Qing Chun
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University Chengdu 610500 P. R. China
PetroChina Tarim Oil Company Korla 841000 P. R. China.
RSC Adv. 2019 Oct 21;9(58):33733-33746. doi: 10.1039/c9ra06763a. eCollection 2019 Oct 18.
Oil and gas exploration and development extends from medium-low temperatures to high and ultra-high temperatures with the development of the oil and gas industry. High-temperature deep carbonate reservoir acid fracturing has introduced more stringent requirements, a slower chemical reaction rate and excellent dissolution performance of acid systems, which means that the acid system should still have a certain dissolution ability above 135 °C. A novel water-soluble encapsulated acid (EA), dual controlled by hydrogen ion concentration and temperature, was developed to exploit ultra-high-temperature carbonate reservoirs. The encapsulating material was insoluble and isolated the internal solid acid at high H ion concentrations and low temperatures, but the solid acid was released as the encapsulating material was dissolved at low H ion concentrations and high temperatures. This unique performance was characterized by ESEM, TGA, FTIR, NMR, mechanical performance, solubility, etching performance, and etching fracture conductivity. All the scientific results show that this EA can be applied as a long-distance etching acid controlled by H ion concentration and temperature, without the need for a thickener and emulsifier to reduce the reaction between the rock and the acid near the wellbore. The test results demonstrated that the solid acid had good thermal stability at 135 °C, the encapsulation material was almost insoluble in high acid concentrations (>14%) at any temperature, and the solid acid began to release when the concentration of hydrochloric acid was less than 14% and the temperature was higher than 95 °C. The rock etching and dissolution behavior was better than that of HCl with the same concentration and the etching fracture conductivity was improved by supplementing the consumption of H ions when etching rock. The encapsulating material is completely dissolved after acid fracturing, avoiding reservoir damage by the residue. The described EA is a promising approach for application in acid fracturing of carbonate reservoirs at ultra-high temperature (>135 °C).
随着油气工业的发展，油气勘探开发从低温、中低温延伸至高温、超高温领域。高温深层碳酸盐岩储层酸压裂对酸液体系提出了更严格的要求，即化学反应速率较慢且具有优异的溶解性能，这意味着酸液体系在135℃以上仍应具备一定的溶解能力。为开发超高温碳酸盐岩储层，研制了一种受氢离子浓度和温度双重控制的新型水溶性包裹酸（EA）。包裹材料不溶于水，在高氢离子浓度和低温下将内部固体酸隔离，但在低氢离子浓度和高温下，随着包裹材料溶解，固体酸被释放出来。通过环境扫描电子显微镜（ESEM）、热重分析（TGA）、傅里叶变换红外光谱（FTIR）、核磁共振（NMR）、力学性能、溶解度、刻蚀性能和刻蚀裂缝导流能力对这种独特性能进行了表征。所有科学结果表明，这种包裹酸可作为受氢离子浓度和温度控制的长距离刻蚀酸应用，无需使用增稠剂和乳化剂来减少井筒附近岩石与酸之间的反应。试验结果表明，固体酸在135℃时具有良好的热稳定性，包裹材料在任何温度下于高酸浓度（>14%）中几乎不溶，当盐酸浓度小于14%且温度高于95℃时，固体酸开始释放。岩石刻蚀和溶解行为优于相同浓度的盐酸，并且在刻蚀岩石时通过补充氢离子消耗提高了刻蚀裂缝导流能力。酸压裂后包裹材料完全溶解，避免了残渣对储层的损害。所述包裹酸是一种在超高温（>135℃）碳酸盐岩储层酸压裂中具有应用前景的方法。
