## 2 Geological Setting  
The Junggar Basin is located in northwestern China (Figure 1a) at the tectonic junction of the Kazakhstan, Tarim, and Siberian plates. It is composed of a stable cratonic block and surrounding fold belts, covering an area of approximately 134,000 km\({}^{2}\)[26]. The Dixi area is situated in the western margin of the Dinnan Uplift, within the eastern Junggar Basin of northwestern China (Figure 1b). Structurally, this area lies at the intersection of several second-order tectonic units, including the Dishuiquan Depression to the north and the Dongdaohaizi Depression to the south, which together form a structurally complex yet hydrocarbon-favorable setting (Figure 1c). These depressions act as hydrocarbon-generation centers, while the Dixi area serves as a migration and accumulation zone for natural gas [27; 28]. The basin architecture in this region reflects a multi-phase tectonic evolution that has influenced source rock development and hydrocarbon migration. In particular, the Dixi area experienced significant tectonic uplift during the Permian and subsequent subsidence during the Mesozoic, creating favorable conditions for hydrocarbon preservation. The regional stratigraphy is characterized by the presence of multiple source-reservoir-seal assemblages, with Upper Carboniferous and Lower Carboniferous coal-bearing formations [29].  
Figure 1: Geological map of the investigated region. (**a**) Geographical position of Junggar Basin in the Chinese territorial context. (**b**) Spatial relationship between the research zone and Junggar Basin boundaries. The highlighted red rectangle demarcates the focal area detailed in panel (**c**). (**c**) Structural framework and hydrocarbon field distribution patterns within the eastern Junggar Basin.  
Situated along the western margin of the Dinnan Uplift, the Dixi region hosts abundant Cretaceous hydrocarbon reserves. Regional exploratory drilling has revealed widespread hydrocarbon indicators, highlighting substantial exploration prospects (Figure 1c). This area features multiple gas-prone source rock sequences spanning Carboniferous through Jurassic periods. Composed predominantly of alternating tufaceous mudstones and volcanic strata (Figure 2), Carboniferous source rocks in the Ludong-Wucaiwan region exhibit TOC concentrations exceeding 1.0%, Type III organic matter, and moderate-to-high thermal evolution (VRo: 1.0-2.0%), demonstrating significant gas-generation capacity [21; 22; 30; 31]. Permian lacustrine mudstones, extensively distributed across the basin, show particularly strong gas potential in the Dongdaohaizi Depression where TOC values surpass 2.5% with mixed Type II-III kerogen and elevated maturity (VRo 1.3-1.5%) [32]. The Lower Carboniferous Dishuiquan Formation presents a transitional marine-terrestrial sequence characterized by conglomerates, sandy conglomerates, siltstones, thick shales, and intermittent coal layers. Similarly to Batamayineishan Formation patterns, these deposits display zonal distribution in the Kelameili foreland, with maximum thicknesses concentrated in the Dishuiquan, Wucaiwan, and Dongdaohaizi depressions. Overlying Permian-Triassic mudstones form effective regional seals, while intra-Carboniferous lithologic variations across depositional cycles create favorable reservoir-caprock configurations. In particular, Permian regional seals effectively preserve hydrocarbons within Carboniferous weathered crust reservoirs [23; 24; 33].  
Figure 2: Generalized stratigraphic sequence in the eastern Junggar Basin region, illustrating principal hydrocarbon reservoir distributions.