Shiyou shiyan dizhi (Jul 2020)
Enrichment characteristics and main controlling factors of shale oil reservoir in the second member of Paleogene Funing Formation, Beigang Subsag, Jinhu Sag, Subei Basin
Abstract
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 Ro 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.
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