## 1 Introduction  
The shale oil and gas revolution in the U.S., with marine shale as the target layer for exploration and development, has achieved great success and changed the world's energy landscape [1, 2]. Since 2010, China's oil and gas industry has drawn on the experience of North America and gradually expanded its exploration target from the traditional confinement to the meridional system and the meridional area, realizing the economic exploitation of China's marine shale oil and gas, and continental shale oil and gas [3, 4, 5]. However, shale reservoirs are characterized by low porosity and low permeability, with almost no natural production capacity. To realize the economic development of shale gas resources, it is necessary to modify the reservoirs through volumetric fracturing to form effective flow channels [6, 7, 8, 9, 10, 11, 12]. Based on hydraulic fracturing technology, the exploitation of marine shale gas has achieved significant success, and three major shale gas fields, including Fuling, Changning, and Weiyuan--in the Wufeng and Longmaxi Formationsof the Sichuan Basin of China, which are particularly large marine shale gas-producing areas--have realized the industrialized exploitation of shale gas by using hydraulic fracturing technology [13; 14; 15]. Compared with marine shale oil and gas reservoirs, continental shale oil and gas reservoirs are characterized by longitudinal lithological interlayers, high viscosity content, and relatively well-developed stratigraphic fractures, which indicates that the relevant technologies applied to marine shale gas development are not fully applicable to continental shale gas development [16; 17; 18; 19; 20]. Therefore, it is particularly important to study the differences in fracture extension in hydraulic fracturing of marine and continental shale. For a long time, scholars at home and abroad have carried out a lot of research on the physical and mechanical properties of shale rock, anisotropy, impact on well wall stability and seam formation effect, etc., to provide strong support for shale gas development [21; 22; 23; 24; 25; 26; 27; 28]. [PERSON] et al. [29] first defined shale reservoir factorability as the nature of a shale's ability to be effectively fractured to increase production. [PERSON] and [PERSON] [30] concluded that the factors affecting the compressibility of shale gas reservoirs mainly include sedimentary formations, stratigraphic properties, mineralogical composition and distribution, and the development of naturally weak surfaces. [PERSON] et al. [31] investigated the anisotropy of Longmaxi shale brittleness based on triaxial mechanical experiments and showed that the brittleness index is affected by the peripheral pressure and the angle of lamination. [PERSON] et al. [32] studied the longitudinal wave velocity and acoustic emission characteristics of Longmaxi Formation shale with different laminar inclinations during uniaxial compression, established the functional relationship between longitudinal wave velocity and strain, and compared the differences in the longitudinal wave velocity and acoustic emission characteristics of shale with different laminar inclinations. [PERSON] et al. [33] showed that the permeability of shale can also exhibit anisotropic characteristics, influenced by the directional distribution of laminae and internal microfractures. [PERSON] et al. [34] analyzed the microfine view mechanism of anisotropy in layered shale by combining X-ray computed tomography (CT) and scanning electron micrography (SEM) techniques, and concluded that the anisotropic characteristics of shale are both intrinsic to its intrinsic properties and related to stress induction, where stress-induced anisotropy is dependent on the orientation of its internal microstructure with respect to the maximum principal stress. The abovementioned studies have relatively limited analyses of the geometric characteristics of fractures after hydraulic fracturing, and there has been no assessment of the productivity enhancement effect of fracturing.