Sun Zepeng, Liu Qipan, Gan Lin, Liu Yashi, Wei Zhifu, Ni Yue
College of Resources and Environment, Shanxi Agricultural University, Taigu 030801, China.
Key Laboratory of Petroleum Resources Exploration and Evaluation Gansu Province, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China.
ACS Omega. 2024 Oct 20;9(43):43914-43926. doi: 10.1021/acsomega.4c07370. eCollection 2024 Oct 29.
Acidification is a promising stimulation technique for improving the pore structure of low-permeability shale reservoirs and enhancing shale gas production. Variations in the mineral composition and acid concentration play a significant role in altering the pore systems in shale reservoirs, thereby affecting shale gas transport and production. To investigate the effect of shale composition on pore structure and fractal characteristics under hydrochloric acid (HCl) treatment, experiments were carried out on carbonate-rich (68%), carbonate-medium (45%), and carbonate-poor (2%) shales with different concentrations of HCl solution (1, 5, 10 wt %). X-ray diffraction (XRD), low-temperature nitrogen adsorption, and fractal theory were performed to investigate variations in mineral composition, pore structure, and fractal characteristics of the unreacted and reacted shales. The results illustrated that the HCl treatment significantly reduced the content of carbonate minerals, and the dissolution degree of carbonate minerals increased with the increase in HCl concentration. More meso- and macropores were generated for carbonate-rich and carbonate-medium shale, while more micro- and mesopores were generated in carbonate-poor shale, which led to the increase in total pore volume (TPV) and total specific surface area (TSSA) at different degrees. Moreover, the pore surface roughness ( ) and structure complexity ( ) were reduced with the increase of HCl concentration for carbonate-rich shale, while the alteration of and showed an opposite trend for carbonate-poor shale. Additionally, decreased and increased for carbonate-medium shale. Relevant results could provide theoretical references for the acid fracturing of shale reservoirs with varying mineral compositions.
酸化是一种很有前景的增产技术，可改善低渗透页岩储层的孔隙结构并提高页岩气产量。矿物成分和酸浓度的变化在改变页岩储层孔隙系统方面起着重要作用，从而影响页岩气的运移和产量。为了研究盐酸（HCl）处理下页岩成分对孔隙结构和分形特征的影响，对富含碳酸盐（68%）、中等碳酸盐含量（45%）和贫碳酸盐（2%）的页岩进行了不同浓度（1、5、10 wt%）HCl溶液的实验。采用X射线衍射（XRD）、低温氮吸附和分形理论来研究未反应和反应后页岩的矿物成分、孔隙结构和分形特征的变化。结果表明，HCl处理显著降低了碳酸盐矿物含量，且碳酸盐矿物的溶解程度随HCl浓度的增加而增大。富含碳酸盐和中等碳酸盐含量的页岩产生了更多的中孔和大孔，而贫碳酸盐页岩产生了更多的微孔和中孔，这导致不同程度的总孔隙体积（TPV）和总比表面积（TSSA）增加。此外，富含碳酸盐页岩的孔隙表面粗糙度（ ）和结构复杂性（ ）随HCl浓度的增加而降低，而贫碳酸盐页岩的 和 的变化趋势相反。此外，中等碳酸盐含量页岩的 减小而 增大。相关结果可为不同矿物成分页岩储层的酸压裂提供理论参考。
