Occurrence Characteristics of Fluids in Shale Oil Reservoirs via a 2D NMR and Frozen Core Analysis: A Case Study of the Jurassic Lianggaoshan Formation in Central Sichuan Basin

The T1-T2 two-dimensional nuclear magnetic resonance (2D NMR) technique, combined with cryogenic core preservation, provides a novel approach to characterize in situ fluid occurrence states in shale oil reservoirs. This study investigates the Jurassic Lianggaoshan Formation in the Sichuan Basin through 2D NMR experiments under frozen (-10 °C) and formation-temperature (60 °C) conditions, followed by measurements on oil-washed, water-saturated, and oil-saturated cores. The results distinguish key components such as bitumen/kerogen (T1/T2 > 100), adsorbed oil (T1/T2 ≈ 5), and free oil (T1/T2 ≈ 1) and reveal that temperature elevation significantly enhances free oil mobility (T2 range expanded by 4.9-fold). A fluid identification chart was established to quantify shale oil movability, offering a practical tool for reservoir evaluation.