The decline of proven conventional petroleum resources in the shallow portions of the Nanpu sag has shifted attention to the exploration of deep unconventional oil and gas resources there, especially the shale oil resources in the middle Eocene shales of the Shahejie Formation (MES shales). In this study, to assess the oil potential of the MES shales, we carried out a systematical geochemical and basin modeling characterization. The results show that the MES shales have low maturity and are at the early stage of hydrocarbon generation, with a mean vitrinite reflectance of 0.64% and low ratio of C₂₇ 18α(H)-22, 29, 30-trisnorneohopane to C₂₇ 17α(H)-22, 29, 30-trisnorhopane (0.44–1.18). The MES shales contain abundant organic matter (OM), with an average total organic carbon content of 2.21 wt %. Biomarker analyses show that the OM in the MES shales derived mainly from floating macrophyte and aquatic algae, microalgae and bacteria. The sapropelinite group in the MES shales is predominant in the organic macerals, and the kerogen is sapropelic and dominated by types I and II₁. Biomarker analyses also reveal that the MES shales were deposited in the stratified water column as suggested by the presence of gammacerane, under relatively warm and wet climatic conditions. The anoxic conditions built up in the water column facilitated the OM preservation, although slight microbial degradation resulted in relatively high carbon preference index values. Modeling results based on geochemical data and basin analyses show that considerable quantities of hydrocarbons remain in the low-maturity MES shales. The preliminary estimate of the quantity of shale oil resources in the Gaoliu area of Nanpu sag is approximately 1.78 × 10⁸ t. Nanpu sag have good shale oil potential, and shale oil exploration may be more feasible for MES shales, especially in the context of in-situ heating technology.

南堡凹陷浅部已探明常规石油资源的减少，已将注意力转向深部非常规油气资源勘探，特别是沙河街组中始新统页岩（MES页岩）页岩油资源。在这项研究中，为了评估 MES 页岩的石油潜力，我们进行了系统的地球化学和盆地建模表征。结果表明，MES页岩成熟度低，处于生烃初期，镜质体平均反射率为0.64%，C ₂₇ 18α(H)-22, 29, 30-trisnorneohopane与C ₂₇的比值较低17α(H)-22, 29, 30-trisnorhopane (0.44–1.18)。MES页岩含有丰富的有机质（OM），平均总有机碳含量为2.21wt%。生物标志物分析表明，MES 页岩中的 OM 主要来自漂浮的大型植物和水生藻类、微藻和细菌。MES页岩中的腐泥岩群以有机质为主，干酪根为腐泥质，以Ⅰ型和Ⅱ型为主₁. 生物标志物分析还表明，在相对温暖和潮湿的气候条件下，MES 页岩沉积在分层水柱中，正如伽马蜡烷的存在所暗示的那样。水体中建立的缺氧条件促进了 OM 的保存，尽管轻微的微生物降解导致相对较高的碳偏好指数值。基于地球化学数据和盆地分析的建模结果表明，在低成熟度 MES 页岩中仍有相当数量的碳氢化合物。初步估算南堡凹陷高柳地区页岩油资源量约为1.78×10 ⁸  t。南堡凹陷具有良好的页岩油潜力，尤其是在原位加热技术的背景下，MES页岩可能更适合进行页岩油勘探。