Comparison of Methods for Determining the Oil Content in Medium-Mature Shale—A Case Study from the Fourth Member of the Shahejie Formation in the Dongying Depression

The oil content of shale oil reservoirs is a key parameter for reserve evaluation and “sweet spot” selection. However, discrepancies in the oil contents obtained by different methods have led to considerable disparities in the selection of exploration well locations and development strategies for shale oil. This study focuses on low to moderately mature sealed coring samples from the Dongying Depression in the Bohai Bay Basin. Three methods—NMR, Dean–Stark, and Rock-Eval—were employed to measure the oil content of shale. The results indicate that the oil content obtained by NMR is the highest, followed by the Dean–Stark distillation extraction method, while the pyrolysis method yields the lowest value. The study found that (1) the efficiency of the solvent extraction effect on moderately to low-mature shale is low since the occurrence of numerous closed pores leads to a lower yield when using the Dean–Stark method. (2) The exposure of shale samples to the air, sample crushing, and lag time for temperature increase cause a significant loss of light hydrocarbon components, resulting in the lowest oil content when measured by the Rock-Eval method. The NMR method, with its advantages of a short analysis time and non-destructive nature, appears to be the most advantageous method for shale oil content evaluation.