Wang Chunxia, Gao Jianliang, Zhang Xuebo
College of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan 454003, China.
School of Mining and Mechanical Engineering, Liupanshui Normal University, Liupanshui, Guizhou 553004, China.
ACS Omega. 2022 Sep 8;7(37):33280-33294. doi: 10.1021/acsomega.2c03810. eCollection 2022 Sep 20.
Acidizing technology is an important means to increase production in oil-gas reservoirs. In recent years, acidizing technology has been widely used to increase the permeability of coal seams to enhance gas extraction, where acidizing fluid is the key factor to determine the permeability improvement effect by acidizing technology. In order to clarify the influence of mixed acid fluid on the pore structure of high rank coal and seek the optimal mixed acid fluid suitable for acidizing and permeability improvement of high rank coal in the Jiaozuo coal mine area. Taking the Jiulishan Mine in the Jiaozuo mining area as an example, low field nuclear magnetic resonance (LFNMR) test and static dissolution test were conducted to obtain the spectrum, porosity, movable fluid saturation, pore throat distribution, nuclear magnetic permeability, and dissolution rate of coal samples before and after treatment with distilled water and three mixed acid fluids. On this basis, the influence of mixed acid fluid on the pore structure of high rank coal was analyzed and the optimal mixed acid fluid suitable for high rank coal was selected. The results showed that the pore size, number, and volume of all kinds of pore sizes of coal samples treated with distilled water all decreased, which was manifested by the decrease of effective porosity and nuclear magnetic permeability. After acidification, the proportion of micropore volume in coal decreased significantly, the number and proportion of pore volume of mesopores and macropore-microfractures increased significantly, and the connectivity between mesopores and macropore-microfractures was enhanced, which was characterized by the increase in effective porosity and nuclear magnetic permeability of coal samples. After acidification, the pore-throat ratio of adsorption pores of all coal samples decreased, while the pore-throat ratio of seepage pores increased. By comparatively analyzing the change law of pore structure of coal samples before and after acidizing with three kinds of mixed acid fluids, the optimal mixed acid fluid suitable for acidizing and permeability improvement of high rank coal in the Jiaozuo coal mine area was selected, which was 12%HCL +3%HF.
酸化技术是提高油气藏产量的重要手段。近年来，酸化技术已被广泛应用于提高煤层渗透率以增强瓦斯抽采，其中酸化液是决定酸化技术提高渗透率效果的关键因素。为阐明混合酸液对高阶煤孔隙结构的影响，探寻适合焦作矿区高阶煤酸化增透的最优混合酸液。以焦作矿区九里山矿为例，进行了低场核磁共振（LFNMR）测试和静态溶蚀试验，获得了蒸馏水及三种混合酸液处理前后煤样的谱图、孔隙度、可动流体饱和度、孔喉分布、核磁渗透率和溶蚀率。在此基础上，分析了混合酸液对高阶煤孔隙结构的影响，筛选出了适合高阶煤的最优混合酸液。结果表明，蒸馏水处理后的煤样各种孔径的大小、数量和体积均减小，表现为有效孔隙度和核磁渗透率降低。酸化后，煤中微孔体积占比显著降低，中孔和大孔 - 微裂隙的孔体积数量和占比显著增加，且中孔与大孔 - 微裂隙之间的连通性增强，表现为煤样有效孔隙度和核磁渗透率增加。酸化后，各煤样吸附孔的孔喉比降低，渗流孔的孔喉比增加。通过对比分析三种混合酸液酸化前后煤样孔隙结构的变化规律，筛选出了适合焦作矿区高阶煤酸化增透的最优混合酸液为12%HCl + 3%HF。
