Abstract A total of 19 representative lacustrine shale (core) samples from the Upper Cretaceous Qingshankou Formation in the Changling Sag, Songliao Basin, northeast China have been characterized to determine the types of shale oil reservoir lithofacies and investigate pore structures and pore-scale oil distribution using an integrated petrographic, geochemical and petrophysical approach. Based on the sedimentary structures and mineral compositions, four lithofacies types have been recognized: foliaceous argillaceous mudstone (FAM), laminated diamictic mudstone (LDM), laminated felsic mudstone (LFM) and interbedded felsic mudstone (IFM). Sequential extraction experiments via a Soxhlet extractor were performed using different solvents to recover oils of varying polarities: weak-polar oil (WPO) was extracted with n-hexane under room temperature, while strong-polar oil (SPO) was extracted with a mix of dichloromethane and methanol (9:1 v/v) extraction. Low-pressure N2 sorption data acquired from the original and solvent extracted samples indicates that the pore volumes occupied by WPO (VWPO) decrease progressively in LFM (averaging 68.32 × 10−4 cm3/g), LDM (averaging 50.41 × 10−4 cm3/g), FAM (averaging 48.86 × 10−4 cm3/g) and IFM (averaging 39.39 × 10−4 cm3/g); while pore volumes occupied by SPO (VSPO) increase progressively in IFM (averaging 8.00 × 10−4 cm3/g), LFM (averaging 12.62 × 10−4 cm3/g), LDM (averaging 38.85 × 10−4 cm3/g) and FAM (averaging 65.08 × 10−4 cm3/g). Major factors controlling pore-scale oil distribution in the shale reservoirs include pore structures, TOC and clay mineral contents. Pore structures can affect the distribution of WPO and SPO to a great extent. WPO is mainly distributed in the mesopores, while SPO is present in all pores in the four lithofacies. SPO is mainly distributed in mesopores in FAM and LDM, and in macropores in LFM and IFM. TOC and clay mineral contents have strong impacts on the distribution of SPO. Carbonate minerals in LDM and IFM are dominated by ostracoda shells and authigenic calcite cement, respectively. The carbonate mineral content shows a positive correlation with WPO in LDM, in which the carbonate minerals are dominated by ostracoda shells with well-developed pores due to organic acid dissolution. TOC shows a positive correlation with WPO for TOC less than 1.2 wt%, while shows a negative correlation for TOC greater than 1.2 wt%. In the study area, LDM and LFM are identified as favorable lithofacies or “sweet spots” for shale oil exploration because they have relatively high TOC (0.7–2 wt%), high percentages of in situ WPO and a high mineral brittleness index.

中文翻译：

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松辽盆地长岭凹陷青山口组页岩孔隙尺度油气分布

摘要 对松辽盆地长岭凹陷上白垩统青山口组19个代表性湖相页岩（岩心）样品进行表征，确定页岩油储层岩相类型，研究孔隙结构和孔隙尺度石油分布。使用综合的岩石学、地球化学和岩石物理方法。根据沉积构造和矿物组成，已识别出四种岩相类型：叶质泥质泥岩（FAM）、叠层混杂泥岩（LDM）、层状长英质泥岩（LFM）和互层长英质泥岩（IFM）。通过索氏提取器进行连续提取实验，使用不同的溶剂回收不同极性的油：弱极性油 (WPO) 在室温下用正己烷提取，而强极性油 (SPO) 则采用二氯甲烷和甲醇 (9:1 v/v) 混合萃取法进行萃取。从原始样品和溶剂提取样品获得的低压 N2 吸附数据表明，WPO (VWPO) 占据的孔隙体积在 LFM（平均 68.32 × 10−4 cm3/g）、LDM（平均 50.41 × 10−4 cm3 /g)、FAM（平均 48.86 × 10−4 cm3/g）和 IFM（平均 39.39 × 10−4 cm3/g）；而 SPO (VSPO) 占据的孔隙体积在 IFM（平均 8.00 × 10−4 cm3/g）、LFM（平均 12.62 × 10−4 cm3/g）、LDM（平均 38.85 × 10−4 cm3/g）中逐渐增加和 FAM（平均 65.08 × 10−4 cm3/g）。控制页岩储层孔隙尺度石油分布的主要因素包括孔隙结构、TOC 和粘土矿物含量。孔隙结构在很大程度上影响 WPO 和 SPO 的分布。WPO 主要分布在介孔中，而 SPO 存在于四种岩相的所有孔隙中。SPO主要分布在FAM和LDM中的介孔中，LFM和IFM中主要分布在大孔中。TOC 和粘土矿物含量对 SPO 的分布有很大影响。LDM 和 IFM 中的碳酸盐矿物分别以介形壳和自生方解石胶结物为主。碳酸盐矿物含量与 LDM 中的 WPO 呈正相关，其中碳酸盐矿物以介形壳为主，由于有机酸溶蚀，孔隙发育良好。TOC 小于 1.2 wt% 时，TOC 与 WPO 呈正相关，而 TOC 大于 1.2 wt% 时，TOC 与 WPO 呈负相关。在研究区，