# NMR Evaluation of Shale Oil Mobility: Combined Pyrolysis and CO\({}_{2}\) [PERSON]
## 1 Introduction
Compared to conventional sandstone reservoirs, shale contains multiple hydrogen-containing components, including movable oil, water, kerogen, structural water, clay-bound water, asphaltene, and other signals. The conventional one-dimensional (1D) NMR \(T_{2}\) spectrum, being a composite response of NMR signals from various fluid components in the rock, often fails to clearly distinguish between these components in shale [11; 12]. The two-dimensional (2D) NMR \(T_{1}\)-\(T_{2}\) method can effectively avoid the aforementioned issues. The 2D NMR method takes advantage of the different molecular diameters of hydrogen-containing substances, resulting in more significant differences on the \(T_{1}\)-\(T_{2}\) spectrum. This method enables the identification of different hydrogen-containing components using a reference template, becoming the main approach for NMR-based fluid component discrimination in shale oil [13; 14; 15; 16; 17; 18]. Scholars have observed variations in the position and morphology of identical fluids across 2D fluid component templates constructed from NMR experiments on diverse shale samples. These discrepancies arise from variations in the geological settings, diagenetic histories, and laboratory-specific measurement parameters of shale samples. All of these factors can influence NMR response features and introduce variability in the measurement results. [PERSON] et al. compared the results of Bakken shale measured on NMR instruments at 2 MHz and 400 MHz frequencies and found that high-field NMR can help identify the solid organic matter and clay-bound water components of shale [19]. Furthermore, they also conducted NMR measurements on extracted kerogen and asphalt from shale, suggesting that different frequency instruments and temperature environments can affect the morphological distribution of measured fluid components [20]. [PERSON] et al. used a 21 MHz NMR core analyzer to conduct tests on shale from the Bohai Bay Basin, and concluded that terrestrial and marine shale have different fluid component distributions due to different depositional environments [21]. The current research highlights the substantial benefits of 2D NMR for shale component identification, enabling the accurate recognition and partition of components, but it still requires assistance from other experimental techniques, which is also the focus and challenge in the field of 2D NMR component analysis. In shale oil development, the CO\({}_{2}\) huff-n-puff process effectively sustains reservoir pressure and provides a driving force for oil recovery [22; 23; 24; 25; 26]. CO\({}_{2}\) has strong diffusivity and low viscosity, and it is soluble in oil. Upon dissolution, it reduces oil viscosity, enhances pore mobility, and consequently, improves the recovery rate of shale oil. Moreover, CO\({}_{2}\) huff-n-puff technology enables the sequestration of CO\({}_{2}\) underground, facilitating carbon capture, utilization, and storage (CCUS). Laboratory analyses of shale oil mobility through CO\({}_{2}\) huff-n-puff are valuable for practical development scenarios. Studies have demonstrated that CO\({}_{2}\) injection can efficiently mobilize oil within the reservoir rock, with mechanisms primarily involving oil expansion and diffusion of concentration gradients. Under Bakken reservoir conditions, the use of well-preserved natural cores in supercritical CO\({}_{2}\) extraction experiments has yielded a recovery rate of up to 60% [27; 28]. Thus, employing CO\({}_{2}\) huff-n-puff in shale oil reservoirs can attain high recovery rates, necessitating injection pressures above the minimum miscibility pressure [29]. Numerical simulations indicate that CO\({}_{2}\) huff-n-puff may enhance recovery rates in shale oil reservoirs to 22.5%, potentially surpassing 40% in fully miscible conditions [30]. When compared to gas driving, CO\({}_{2}\) huff-n-puff has shown superior effectiveness in recovery rate enhancement.