A novel method for quantitative characterization of organic matter based on NMR FID acquisition mode

Continental shale oil reservoirs in China are abundant in Solid Organic Matter (SOM), which represents a significant potential hydrocarbon resource. Nuclear Magnetic Resonance (NMR) is an effective tool for evaluating shale oil reservoirs. However, restricted by instrument dead time, it is difficult for the conventional CPMG acquisition mode to capture signals from ultra-short relaxation components such as SOM.To address this, this work introduces the Free Induction Decay (FID) acquisition mode, proposing two novel quantification workflows based on FID signal integration and a direct T₁-T₂^* spectrum, respectively. These approaches are designed to effectively capture the ultra-short components that are typically missed by standard CPMG sequences.The proposed methodology was validated against comprehensive geochemical benchmarks. The results demonstrate that the FID-driven approach yields a superior correlation with geochemical data compared to conventional methods. It exhibits high statistical consistency with Step-by-Step (SBS) Rock-Eval pyrolysis data, proving its capability to accurately quantify total solid hydrogen content, including solid petroleum hydrocarbons, bitumen, and kerogen. This work provides a non-destructive and high-precision means for evaluating the resource potential of shale oil reservoirs.