松辽盆地长岭凹陷乾安地区青山口组一段沉积相特征与古环境恢复——以吉页油1井为例

松辽盆地上白垩统青山口组一段富有机质泥页岩岩发育,层系内部滞留烃富集,具有可观的页岩油资源潜力。沉积古环境控制了泥页岩的分布、有机质发育特征及滞留烃富集程度。因此,恢复青一段泥页岩沉积古环境,明确沉积特征,对揭示青一段泥页岩中页岩油富集规律具有重要意义。本文基于长岭凹陷乾安地区青一段取心井——吉页油1井的岩心观察及测井曲线组合特征,划分了青一段泥页岩沉积微相,应用自然伽马能谱测井、岩性扫描测井数据,选取环境评价参数,对青一段沉积古环境及其演化过程进行了恢复,分析了古环境参数与泥页岩中滞留烃含量的相关性。结果表明:松辽盆地长岭凹陷乾安地区青一段泥页岩是在三角洲外前缘-浅湖-半深湖-深湖沉积体系中形成的,主要发育半深湖-深湖泥、浅湖泥沉积微相。青一段泥页岩沉积古环境经历了水深由浅变深,气候由半潮湿到潮湿,水体由淡水-微咸水,还原性由弱到强,水动力条件由中等到弱的演化,在青一段地层中存在明显的沉积环境变化界面,上下层段沉积环境不同。青一段泥页岩中滞留烃含量主要受沉积古气候、古氧化还原条件控制,潮湿气候还原条件下形成的泥页岩有机质类型好,以腐泥质为主,生油能力强,滞留烃含量高。

Sedimentary characteristics and paleo-environment restoration of the first member of Qingshankou Formation in Qian'an area, Changling sag, Songliao Basin: A case study of Jiyeyou 1 Well

The first member of Upper Cretaceous Qingshankou Formation (K₂qn₁) in Songliao Basin has considerable shale oil resource potential because of the wide development of dark mudstone and high residual hydrocarbons. The paleo-sedimentary environment directly controls the dark mudstone distribution, organic matter development, and residual hydrocarbon content. Therefore, analyzing the sedimentary features and restoring the paleo-environment of K₂qn₁ are of great significance for revealing the regularity of shale oil enrichment. Based on the core observation and logging data of well Jishanyou 1 in Qian''an area of Changling Sag, the authors analyzed the sedimentary characteristics of K₂qn₁. According to the element data obtained by natural gamma ray spectrometry logging and lithologic scanning logging, the evolution of the paleo-environment of K₂qn₁ was restored by using suitable parameters. Furthermore, the correlation of paleo-environment parameters and residual hydrocarbon content in mudstone shale was also studied. The results show that the dark mudstone of K₂qn₁ in the study area was developed in the outer Delta front to shallow lake-semi-deep lake sedimentary system. The palaeo-environment of K₂qn₁ underwent a change of water depth from shallow to deep, climate from semi-humid to humid, salinity from fresh to brackish, reduction conditions from weak to strong, and sedimentary hydrodynamics from moderate to weak. There is an obvious interface of sedimentary environment within K₂qn₁. The content of residual hydrocarbon in the mudstone is mainly controlled by paleo-climate and paleo-reduction conditions. The oil-bearing organic matter was formed in a wet and reducing environment, with strong oil-generating capability and high content of residual hydrocarbon.