Abstract: Shale samples in an open environment, on the one hand, experience significant loss of light
hydrocarbons due to pressure release, and on the other hand, due to temperature reduction, the viscosity of
retained hydrocarbons increases and their state changes, making it difficult to accurately quantify shale oil content
under in-situ temperature and pressure conditions using nuclear magnetic resonance at room temperature. This
study takes the Qingshankou Formation shale of the Cretaceous from the Songliao Basin as an example, typical
shale samples in the low and high maturity stages were selected. Nuclear magnetic resonance detection were
performed on high mature shale samples with different degrees of pulverization, as well as low and high mature
shale samples under different temperature conditions, to quantify the fluid loss and state transformation during
the pulverization and heating processes, and determine the oil content characteristics under the influence of
temperature. The results showed that during the process of crushing shale from standard plunger to ~0.04 cm, the
morphology of its T2 spectrum, the total signal amount of T1-T2 spectrum, and the signal amount of each
hydrogen containing component remained basically unchanged. Therefore, prolonged exposure to shale samples
during the crushing process will not result in significant residual fluid loss. As the temperature of shale samples
increases, the light oil signal increases and the water signal decreases in low mature shale, while the oil and water
signals decrease in high mature shale. At the same time, the signal of hydroxyl compounds in shale decreased,
and its signal level was restored after returning to room temperature. It can be seen that as the temperature
increases, free water continues to evaporate; The pre-oil bitumen of low mature shale with high viscosity at room
temperature changes from a solid-like state to a liquid light oil. After 100 ℃, the absolute amount of NMR light
oil increases by 107%; In high mature, the shale oil bitumen becomes light oil at room temperature, and heating
will cause it to evaporate and dissipate. The decrease and increase of hydroxyl containing compounds with
temperature rise and fall reflects the controlling effect of temperature on clay adsorption of water. Therefore,
when using NMR to evaluate the oil content of low mature shale, attention should be paid to the transformation of
the pre-oil bitumen under temperature conditions to avoid underestimating the shale oil content.