Zhang Pengfei, Lu Shuangfang, Li Junqian, Wang Junjie, Zhang Junjian, Yin Yajie
College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, Shandong, China.
Sanya Offshore Oil & Gas Research Institute, Northeast Petroleum University, Sanya 572025, Hainan, China.
ACS Omega. 2023 Jul 16;8(29):26508-26525. doi: 10.1021/acsomega.3c03260. eCollection 2023 Jul 25.
Heat treatment plays a significant role in determining the petrophysical properties of shale reservoirs; however, the existing studies on the evolution of pore structures are still insufficient. This study conducts a series of tests, including Rock-Eval, low-temperature nitrogen adsorption-desorption, nuclear magnetic resonance (NMR) , and - tests on samples from Shahejie Formation, Dongying Sag, Bohai Bay Basin. The tests aim to determine the changes in the shale pore structures under increasing heat treatments (ranging from 110 to 500 °C) and identify the factors that control pore structures. The results show that the gradual decomposition of organic matter leads to an eventual decrease in the total organic carbon (TOC) content. The decrease in TOC is more prominent when the temperature exceeds 300 °C. For shales with lower TOC contents (<2%), the Brunauer-Emmett-Teller specific surface area (BET SSA) first decreases, then increases, but eventually decreases again. However, the average pore diameter demonstrates an opposite trend when the temperature increases. In contrast, for organic-rich shales (TOC > 2%), the BET SSA increases at temperatures above 200 °C. The similarity between the values implies that the complexity and heterogeneity of shale pore surface only undergo minor changes during heat treatment. Porosity shows an increasing trend, and the higher the contents of clay minerals and organic matter in shales are, the greater the change in porosity is. The NMR spectra suggest that micropores (<0.1 μm) in shales first decrease and then increase, whereas the contents of meso- (0.1-1 μm) and macropores (>1 μm) increase, corresponding to the increase in free shale oil. Moreover, shale pore structures are primarily controlled by clay minerals and organic matter contents during heat treatments, with higher contents resulting in better pore structures. Overall, this study contributes to detailing the shale pore structure characteristics during the in situ conversion process (ICP).
热处理在确定页岩储层岩石物理性质方面起着重要作用；然而，目前关于孔隙结构演化的研究仍然不足。本研究对渤海湾盆地东营凹陷沙河街组的样品进行了一系列测试，包括岩石热解、低温氮吸附-脱附、核磁共振（NMR）等测试。这些测试旨在确定在升温热处理（110至500℃）下页岩孔隙结构的变化，并识别控制孔隙结构的因素。结果表明，有机质的逐渐分解最终导致总有机碳（TOC）含量下降。当温度超过300℃时，TOC的下降更为明显。对于TOC含量较低（<2%）的页岩，布鲁诺尔-埃米特-特勒比表面积（BET SSA）先减小，然后增大，但最终又减小。然而，平均孔径在温度升高时呈现相反的趋势。相比之下，对于富含有机质的页岩（TOC>2%），在200℃以上温度下BET SSA增大。这些值之间的相似性意味着页岩孔隙表面的复杂性和非均质性在热处理过程中仅发生微小变化。孔隙度呈增加趋势，页岩中粘土矿物和有机质含量越高，孔隙度变化越大。NMR谱表明，页岩中的微孔（<0.1μm）先减少后增加，而中孔（0.1-1μm）和大孔（>1μm）的含量增加，这与游离页岩油的增加相对应。此外，在热处理过程中，页岩孔隙结构主要受粘土矿物和有机质含量控制，含量越高，孔隙结构越好。总体而言，本研究有助于详细了解原位转化过程（ICP）中页岩孔隙结构特征。
