## 1 Introduction  
By the end of 2022, China possessed proven geological reserves of terrestrial shale oil amounting to 1.306 billion tons, with controlled reserves totaling 128 million tons and predicted reserves estimated at 2.974 billion tons [1]. In 2022, the production of continental shale oil reached approximately 3.18 million tons of crude oil, making it a vital contributor to the stable crude oil production in China [2; 3; 4]. At present, shale oil exploration in the Chinese Mainland has successfully developed high-yield wells in the Paleogene Funing Formation shale system of the Qintong Sag and the Gaoyou Sag in the Subei Basin, with proven reserves of 1.1 billion tons [5; 6], underscoring the significant resource potential of shale oil in China [7]. Nevertheless, when juxtaposed with the marine shale formations discovered in the United States, it becomes evident that China's geological structure exhibits a considerable level of intricacy. The presence of multiple stages of tectonic transformations and frequent climate changes have resulted in complex mineral compositions and significant heterogeneity within continental shale [2; 8; 9]. Moreover, shale oil demonstrates notable attributes, including the elevated viscosity of crude oil, relatively low level of maturity, constrained productivity of individual wells, brief periods of stable production, uneven distribution of wells with high and low production rates, diminished overall recovery rates, and suboptimal economic returns [3; 10]. The aforementioned challenges have played a significant role in the formidable obstacles encountered during the extensive exploration and economic development of continental shale oil in China [3; 11; 12]. The pore structure and developmental characteristics of shale play a crucial role in determining the distribution and accessibility of shale oil, thereby influencing the overall effectiveness of shale-oil extraction. Hence, the assessment of shale reservoirs heavily relies on the analysis of pore characteristics in shale formations. Several methodologies are utilized for this objective; nevertheless, each approach is accompanied by specific constraints stemming from its fundamental principles [13]. Techniques such as the core-casting of thin sections and scanning electron microscopy (SEM) allow for the visual examination of shale pores. However, these methods have limitations in terms of sample size and fail to offer a comprehensive depiction of the pore structure characteristics of the sample. The comprehensive understanding of shale pore structure is affected by different adsorbates, posing a challenge to employing single adsorbate techniques like gas adsorption and mercury intrusion to fully capture the relevant information. In order to achieve a comprehensive characterization, it is typically imperative to augment these methodologies with experimental investigations encompassing carbon dioxide and nitrogen adsorption, along with mercury intrusion [14; 15]. Significantly, the gas adsorption method necessitates sample crushing, which can result in damage to the sample's pore structure, potentially compromising data accuracy [16]. Nano-CT technology and small-angle scattering technology offer non-destructive and quantitative means to characterize shale pore structure [17]. Nevertheless, the implementation of these methods may be financially unfeasible. Conversely, the nuclear magnetic resonance (NMR) technique remains largely unaffected by the composition of the shale skeleton. The aforementioned technology possesses notable characteristics, including high velocity, a non-invasive nature, the ability to conduct measurements across multiple parameters and dimensions, and a comparatively affordable price. Consequently, nuclear magnetic resonance (NMR) has become an indispensable instrument for investigating the pore characteristics of shale reservoirs [18; 19; 20].