Occurrence characteristics of shale oil and lower-limit of oil-bearing in Jimsar Sag.

The occurrence state and the oil-bearing lower limits of shale oil restrict the oil abundance and recoverability of the reservoir. The occurrence characteristics of shale oil were qualitatively characterized by focused on beam scanning electron microscopy, 2D nuclear magnetic resonance (2D NMR), and mercury intrusion experiments before and after extraction. Meanwhile, based on the results of 2D NMR and mercury intrusion experiments, the oil-bearing throat and pore lower limits of the shale oil reservoir in the study area were determined. The research shows that the shale oil heavy components of the Lucao-gou Formation in Jimsar Sag are relatively high and mainly adhere to the hole wall. The light component is mainly stored inside the pores. With the decrease in pore size, the content of heavy components gradually increases. For non-fresh core samples, due to elastic release oil expulsion and volatilization, the residual crude oil is primarily heavy components, which are mainly distributed in T₂ > 0.5 ms, T₁/T₂ = 3 -100 regions on the 2D nuclear magnetic spectrum, mainly small to medium pores. The adsorbed water often exists in the micro-pores, mainly distributed in the areas where T₂ < 0.2 ms and T₁/T₂ = 1-10. Based on the atmospheric spontaneous imbibition and pressure saturation experiments, the fluid distribution characteristics in the saturated state are restored, and the crude oil occurrence characteristics of "large pores with more mobility, middle pores with more Ending, and small pores with more adsorption" are revealed. 2D NMR experiments results show that the oil-bearing lower limit Is T₂ = 0.2- 0.5 ms, which corresponds to a throat radius of about 15 nm. The lower limit of the oil-bearing pore radius is not fixed, which controlled by the dual effects of the lithology and physical property, and its value is distributed in 24- 135 nm. Under the same lithology, as the physical property of the reservoir be-comes better, the oil-bearing throat diameter remains unchanged, but the lower limit of the pore diameter gradually increases, indicating that the ink-bottle shaped ball-stick type pore-throat system more developed in the reservoir with good physical property, and on the contrary, the pipe-shaped branch-lick type pore-throat system more developed. The results provide a reference for the optimization and mobility evaluation of "sweet spot" layers. [ABSTRACT FROM AUTHOR]