Zhang Yingna, Zhou Fei, Chen Guo, Pei Ziwei, Wen Zhigang, Wu Yunzhao, Xu Yaohui
Hubei Key Laboratory of Petroleum Geochemistry and Environment, College of Resources and Environment, Yangtze University, Wuhan 430100, China.
Research Institute of Exploration and Development, PetroChina Qinghai Oilfield Company, Dunhuang 736202, China.
ACS Omega. 2024 Jun 13;9(25):27722-27738. doi: 10.1021/acsomega.4c03956. eCollection 2024 Jun 25.
Oligocene-Pliocene shale reservoirs in the Western Qaidam Depression represent typical mixed shale deposits characterized by moderate organic matter (OM) abundance and sufficient OM maturity, indicating substantial shale-oil resource potential. Here, a comprehensive study was conducted to analyze the reservoir characteristics of different shale types, including the Upper Xiaganchaigou (late Oligocene), Shangganchaigou (Miocene), and Xiayoushashan (early Pliocene) Formations in the Western Qaidam Depression. Our analysis focused on the pore structural characteristics of shale reservoirs, employing X-ray diffraction, casting thin sections, scanning electron microscopy, low-temperature nitrogen adsorption, and nuclear magnetic resonance (NMR) as investigative techniques. Our results show that (1) the study area comprises five typical shale types: lime shale, argillaceous shale, limestone, argillaceous limestone, and mudstone. The best hydrocarbon source rock conditions are found in the lime shale and argillaceous shale. (2) Inorganic pores, including dissolution pores, intergranular pores, bedding fractures, structural fractures, and intraparticle pores in clay minerals, are the main pore types found in the studied samples and constitute the primary reservoir space for shale oil. On the basis of fractal dimensions obtained through NMR, the pores can be classified as micropores (<100 nm), mesopores (100-1000 nm), or macropores (>1000 nm). Mesopores are the main contributors to porosity. (3) The development of micropores is positively correlated with clay mineral content. The development of mesopores and macropores is influenced by the quartz, feldspar, dolomite, and calcite contents. Calcite content exhibits a negative correlation with porosity, suggesting that later-stage pore cementation hinders shale reservoir development. (4) The five typical shale reservoirs in the study area can be categorized into three types. Type I reservoir lithologies include lime shale and argillaceous shale; type II reservoir lithologies include limestone and argillaceous limestone; and type III reservoirs comprise mudstone. Type I and II reservoirs are of better quality than type III.
柴达木盆地西部渐新世 - 上新世页岩油藏是典型的混合型页岩沉积，有机质丰度适中，成熟度较高，具有巨大的页岩油资源潜力。本文对柴达木盆地西部不同层位的页岩储层特征展开了综合研究，这些层位包括上干柴沟组（晚渐新世）、干柴沟组（中新世）和下油砂山组（早上新世）。分析聚焦于页岩储层的孔隙结构特征，采用X射线衍射、铸体薄片、扫描电子显微镜、低温氮气吸附以及核磁共振（NMR）等研究方法。研究结果表明：（1）研究区发育5种典型页岩类型，即灰质页岩、泥质页岩、石灰岩、泥灰岩和泥岩，其中灰质页岩和泥质页岩的烃源岩条件最佳。（2）无机孔隙是研究样品中的主要孔隙类型，包括溶蚀孔隙、粒间孔隙、层理缝、构造缝以及黏土矿物内的颗粒内孔隙，构成了页岩油的主要储集空间。基于核磁共振得到的分形维数，孔隙可分为微孔（<100 nm）、中孔（100 - 1000 nm）和大孔（>1000 nm），其中中孔是孔隙度的主要贡献者。（3）微孔发育与黏土矿物含量呈正相关，中孔和大孔发育受石英、长石、白云石和方解石含量影响，方解石含量与孔隙度呈负相关，表明后期孔隙胶结作用不利于页岩储层发育。（4）研究区5种典型页岩储层可分为3类，Ⅰ类储层岩性为灰质页岩和泥质页岩；Ⅱ类储层岩性为石灰岩和泥灰岩；Ⅲ类储层为泥岩，Ⅰ类和Ⅱ类储层质量优于Ⅲ类。
