Liang Shuo, Tang Tong, Wang Tao, Deng Ze, Zhu Gengen, Wang Daxing
School of Resources and Environment, Yangtze University, Wuhan 430100, P. R. China.
Jiqing Oilfield Operation District, Xinjiang Oilfield Company, PetroChina, Jimsar, Xinjiang 831700, P. R. China.
ACS Omega. 2024 Dec 16;9(52):51363-51378. doi: 10.1021/acsomega.4c08141. eCollection 2024 Dec 31.
The pore structure of shale is a key factor affecting the occurrence and flow of shale gas, and fractal dimensions can be used to quantitatively describe the complexity of the shale pore structure. In this study, the Leping Formation shale in the Junlian block of the southern Sichuan Basin was investigated. The pore structure characteristics of this shale were examined via low-pressure CO adsorption (LP-COA) and low-temperature N adsorption (LT-NA) methods via field emission scanning electron microscopy (FE-SEM), shale geochemistry, and mineral composition analysis. Pore fractal dimensions were calculated via the Frenkel-Halsey-Hill (FHH) model, and the relationships among the fractal dimensions, shale composition (total organic carbon (TOC), quartz, and clay mineral contents), and pore structure were discussed. The results revealed that the TOC contents of the Leping Formation shale in the study area were high and ranged from 0.9% to 4.48%, with an average of 2.25%. The quartz contents were 17.2% to 60.1%, and the clay mineral contents were 33.8% to 67.2%. On the basis of the FE-SEM and N adsorption-desorption curve analyses, the pore types of the Leping Formation shale were complex and significantly variable in terms of the scale and development of organic pores, intragranular pores, and microfractures. The pore morphologies were mostly narrow slit-type flat pores and four-sided open or cone-type flat pores. The pore size distribution exhibited a multimodal pattern. The pore type was mainly mesopores, followed by micropores and minimal macropores. The specific surface area (SSA) of micropores accounted for more than 78% of the total SSA. The fractal dimension of the shale ranged from 2.262 to 2.618 (with a mean of 2.519), and the fractal dimension ranged from 2.662 to 2.843 (with a mean of 2.739). was greater than , indicating that the internal structure of the pores was significantly more complex than that of the surface. The TOC and clay mineral contents were positively correlated with the Brunauer-Emmett-Teller (BET) SSA and the Barret-Joyner-Halenda (BJH) PV, whereas the quartz content was negatively correlated with the BET SSA and BJH PV. The considered fractal dimensions were positively correlated with the TOC content, clay mineral content, BET SSA, and BJH PV but negatively correlated with the quartz content and average pore diameter. The complexity and heterogeneity of the pore structure of the studied shale were quantitatively evaluated through fractal dimension analysis; thus, this approach can be applied in studies of the characteristics of the shale pore structure distribution and reservoir evaluation.
页岩的孔隙结构是影响页岩气赋存与渗流的关键因素，分形维数可用于定量描述页岩孔隙结构的复杂性。本研究对四川盆地南部筠连区块的乐平组页岩进行了调查。通过场发射扫描电子显微镜（FE-SEM）、页岩地球化学和矿物成分分析，采用低压CO吸附（LP-COA）和低温N吸附（LT-NA）方法研究了该页岩的孔隙结构特征。通过Frenkel-Halsey-Hill（FHH）模型计算孔隙分形维数，并讨论了分形维数、页岩成分（总有机碳（TOC）、石英和粘土矿物含量）与孔隙结构之间的关系。结果表明，研究区乐平组页岩的TOC含量较高，范围为0.9%至4.48%，平均为2.25%。石英含量为17.2%至60.1%，粘土矿物含量为33.8%至67.2%。基于FE-SEM和N吸附-脱附曲线分析，乐平组页岩的孔隙类型复杂，有机孔隙、粒内孔隙和微裂缝在尺度和发育程度上存在显著差异。孔隙形态大多为窄缝型扁平孔隙和四边开放或锥形扁平孔隙。孔径分布呈现多峰模式。孔隙类型主要为中孔，其次为微孔和极少的大孔。微孔的比表面积（SSA）占总SSA的78%以上。页岩的分形维数范围为2.262至2.618（平均值为2.519），分形维数范围为2.662至2.843（平均值为2.739）。大于，表明孔隙内部结构比表面结构明显更复杂。TOC和粘土矿物含量与Brunauer-Emmett-Teller（BET）SSA和Barret-Joyner-Halenda（BJH）PV呈正相关，而石英含量与BET SSA和BJH PV呈负相关。所考虑的分形维数与TOC含量、粘土矿物含量、BET SSA和BJH PV呈正相关，但与石英含量和平均孔径呈负相关。通过分形维数分析对研究页岩孔隙结构的复杂性和非均质性进行了定量评价；因此，该方法可应用于页岩孔隙结构分布特征研究和储层评价。
