Gas extraction from Coal Bed Methane has proved challenging mainly due to the low permeability of coals. This study investigated a combination of 2 stimulation techniques, Liquid Nitrogen (LN) fracturing and acidizing, to increase pore structure and cleat network connectivity in coals. Microcomputed Tomography (μ-CT) scanning results suggested that a combination of those 2 applications, in either sequence of implementation, has substantial potential in recovering mineralized fractures and inducing new fractures; thus, leading to wide-open cleat networks. X-ray images show that if LN fracturing of coal is preceded by acidizing, the stimulation efficiency increases from more than double the initial value to over 700% of it, where a porosity of 12% can be achieved. Alternatively, the efficiency of acidizing in porosity enhancement can increase from 300% to 530% when a preceding application of LN freezing provides an open cleat network to facilitate acid access to remote areas. Acid diffusion and digital microscopy images also determined that in fractured coal, HCl concentrations of both 1% and 3% can result in desirable demineralization (13% porosity increment), whereas in the acidizing of original coals, 1% HCl might not be promising. Further, the latter experiments created a wide and connected cleat network after LN fracturing of efficiently acid-stimulated coal. Therefore, a combination of two enhanced recovery techniques, acidizing and LN fracturing, was used in this study to achieve a dramatically boosted cleat network in coals. Additionally, an analytical model was developed to predict the acid reaction rate with coal minerals; it had a good match with experimental results.

中文翻译：

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通过酸化和液氮压裂相结合的煤割理网络增产

事实证明，从煤层气中提取天然气具有挑战性，主要是由于煤的渗透性较低。本研究研究了液氮（LN）压裂和酸化这两种增产技术的组合，以增加煤中的孔隙结构和割理网络连通性。微计算机断层扫描 (μ-CT) 扫描结果表明，这两种应用的组合，无论以哪种实施顺序，在恢复矿化裂缝和诱发新裂缝方面都具有巨大潜力；因此，导致了完全开放的夹板网络。 X射线图像显示，如果在对煤进行液氮压裂之前进行酸化，增产效率可以从初始值的两倍以上提高到700%以上，孔隙率可以达到12%。或者，当液氮冷冻的先前应用提供开放割理网络以促进酸进入偏远地区时，酸化在孔隙度增强中的效率可以从 300% 增加到 530%。酸扩散和数字显微图像还确定，在裂隙煤中，1% 和 3% 的 HCl 浓度都可以产生理想的脱矿效果（孔隙度增加 13%），而在原始煤的酸化中，1% HCl 可能效果不佳。此外，后面的实验在有效酸刺激煤的液氮压裂后创建了一个广泛且连接的割理网络。因此，本研究结合使用了酸化和液氮压裂这两种提高采收率的技术，以实现煤中割理网络的显着增强。此外，还开发了一个分析模型来预测与煤矿物的酸反应速率；与实验结果吻合较好。