## 1 Introduction  
After the marine shale gas in China has achieved industrial production, the development of continental shale oil has also become a key target of unconventional energy sources [1]. The shale refers to the fine-grained sedimentary rock that is composed of clasts, clays, and organic matter with a particle size of less than 0.0039 mm, which has a dense laminated structure [2, 3]. Moreover, the marine shale is mainly deposited in the deep-water shelf, whereas the continental shale is deposited in lake faces [4, 5]. The marine shale is represented by the Longmaxi Formation in the Sichuan Basin and its surrounding areas (Figure 1a), and is characterized by high brittle mineral content, low porosity, and low permeability [6, 7]. Furthermore, the continental shale is represented by the Yanchang Formation in the Ordos Basin (Figure 1b), mainly consisting of gray-black laminas shale. Different from the Longmaxi Formation, the content of brittle minerals in the Yanchang Formation is relatively low, with a high content of clay minerals [8, 9]. At present, hydraulic fracturing is an essential technology for shale oil and gas development to increase reservoir permeability [10, 11]. However, conventional hydraulic fracturing methods are challenging to obtain industrial production because of the high content of clay minerals, rich laminas, and the strong sedimentary heterogeneity in continental shale. The main restriction of fracture propagation in shale is the microstructure and geo-mechanical properties [12; 13]. Studying the micro-mechanism of the difference in macro-physical properties of two kinds of shale is crucial for developing and utilizing shale resources.  
The current research methods for pore structure mainly include N\({}_{2}\)/CO\({}_{2}\) isotherm adsorption and FIB-SEM. The former is an indirect method which indirectly uses gas adsorption data to characterize the complexity of the pore structure [14; 15]. In contrast, FIB-SEM can accurately obtain the proportion of organic matter with the help of image processing methods and perform threshold segmentation according to the distribution of the pores [16]. The geomechanical properties are mainly compressive strength, elastic modulus, and Poisson's ratio. Besides the reservoir properties parameters, including porosity and permeability, all these parameters are critical for hydraulic fracturing and reservoir numerical simulation [17; 18].  
At present, recent developments in unconventional shale oil and gas resources have heightened the need for understanding in the pore structure of reservoirs. Previous studies have reported the basic parameters of marine shale and continental shale [4; 19; 20; 21], and the pore parameters control factors also have been discussed, including the thermal maturity, mineral composition, and TOC content [14; 22; 23; 24; 25]. However, there are few comparative studies between marine and continental shale [26; 27]. In particular, the mechanism of the pore structure difference remains to be further explained. And whether the above controlling factors still have extensive influence in different lithologies needs to be further discussed.  
This report focuses on the pore structure and petrophysical properties differences among marine and continental shale. Forty shale samples were selected from the Longmaxi Formation and Yanchang Formation. The CO\({}_{2}\) & N\({}_{2}\) isotherm adsorption were conducted, combing with the SEM analysis and petrophysical experiments, and the mechanism of the pore parameters differences has been comprehensively discussed.  
Figure 1: Location of Longmaxi Formation in Sichuan Basin (**a**) and Yanchang Formation in Ordos Basin (**b**); The location map of the Sichuan and Ordos Basin in China (**c**).