苏北盆地金湖凹陷北港次洼古近系阜宁组二段页岩油富集特征及主控因素

通过解剖苏北盆地金湖凹陷北港次洼古近系阜宁组二段泥灰质页岩油藏,分析了成藏条件,确定富集主控因素。北港泥灰质页岩油藏埋深3660~3735 m,纵向上位于阜二段③~④亚段,属于典型的源储一体型油藏。油藏具有"四高一发育"特征,即高有机质丰度、高演化程度、高脆性矿物、高异常压力、天然裂缝发育。阜二段③~④亚段灰质泥岩和泥灰岩为优质烃源岩,实测有机碳含量平均为1.83%,S1平均为0.59 mg/g,有机质类型为Ⅰ型,Ro为1.1%,成熟度较高。原油的植烷、伽马蜡烷、孕甾烷、三环萜烷含量中等,形成于半咸水的烃源岩。阜二段泥灰岩脆性矿物含量平均为60.7%,以石英、白云石和方解石为主,实测孔隙度4.24%~8.76%,平均为7.04%;③亚段溶蚀孔发育,④亚段天然裂缝发育,声波时差计算压力系数为1.3。大面积分布的优质烃源是页岩油藏形成的物质基础,地质甜点控制页岩油局部富集,高异常压力是页岩油藏高产的关键,阜二段泥灰质页岩油藏具有较好的勘探开发前景。

Enrichment characteristics and main controlling factors of shale oil reservoir in the second member of Paleogene Funing Formation,Beigang Subsag,Jinhu Sag,Subei Basin

The accumulation conditions were studied and the main controlling factors were determined based on the analysis of marly shale reservoirs in the second member of Paleogene Funing Formation in the Beigang Subsag, Jinhu Sag, Subei Basin. The Beigang marly shale reservoir is buried 3 660-3 735 m, in the ③-④ subsections of the second member of Funing Formation. It is a typical self-sourced oil reservoir. The reservoir is characterized by “four high values and one development”, that is, high organic matter abundance, high thermal evolution degree, high brittle mineral content, high abnormal pressure and natural fracture development. The lime mudstones and marls of the ③-④ submembers of the second member of Funing Formation are high-quality source rocks. The average TOC content is 1.83%, and the average S₁ value is 0.59 mg/g. The organic matter type is type Ⅰ, and the R_o value is 1.1%, indicating a high maturity. The crude oil has moderate phytane, gammacerane, pregnane and tricyclic terpane contents indicating deposition in a relatively high salinity environment. The average content of brittle minerals is 60.7%, mainly consisting of quartz, dolomite and calcite. The measured porosity is 4.24%-8.76%, with an average of 7.04%. Solution pores are developed in subsection ③, while natural fractures are developed in subsection ④. The pressure coefficient calculated by acoustic time difference is 1.3. Widespread high-quality source rocks are the material basis for shale reservoir formation. Geological “sweet spots” control the local enrichment of shale oil. High abnormal pressure is critical for the high production of shale reservoir. The marly shale reservoir in the second member of Funing Formation has a good prospect for exploration and development.