## 2 Regional Geological Background  
Since the Late Paleozoic, the Ordos Basin has experienced the influences of the Hercynian Movement, the Indosinian Movement, the Yanshan Movement and the Himalayan Movement, and after each tectonic movement stabilized, the present-day basin topography was formed. The late Paleozoic was in the Hercynian tectonic stage. At this time, the Ordos Basin was a part of the North China Craton and had a stable tectonic background. Owing to the strike closure of the Central Asia-Mongolia Trough and the formation of the fold bundles of the Qinling Trough, under this strong pressure, the tectonic movement of the basin manifested as slow subsidence of the crust [14], and the sedimentary environment included extensive terrestrial fluvial-shallow water delta sediments, with the main development of distributary channels, underwater distributary channels and interdistributary bags [15; 16]. The slow basin subsidence continued until the end of the Indosinian period. Until the Yanshanian period, the basin began to uplift and denudate, the eastern part continued to uplift, and the paleo-geographic pattern of high in the east and low in the west continues to this day [17].  
Located in the northwestern Ordos Basin, the Sulige gas field is the first integral gas field in China with reserves exceeding one trillion cubic meters. In the area, the coal-derived hydrocarbon source rocks are extensively developed in the Benxi Formation, the Taiyuan Formation and the Shanxi Formation 2 members [18], in which the coal seam is 6-20 m thick, the dark mudstone is 40-120 m thick, and the maturity is 0.96-2.96% (1.78% on average). The main producing layers of the Sulige gas field are the He 8 member and the Shan 1 member, which are overlain by a set of clastic rock deposits dominated by mudstone. The mudstone can reach a thickness of 50-120 m and is distributed in a large regional area, forming the regional caprock of the Sulige gas field [19]. The sandstone bodies distributed in the north-south direction were configured with the sedimentary facies of the distributary bay, floodplain and coastal shallow lake laterally, forming a large lithological trap [20].  
Two periods of accumulation occurred in the Sulige gas field, i.e., the initial charging period from the end of the Middle Triassic to the end of the Middle Jurassic and the main charging period from the Late Jurassic to the end of the Early Cretaceous [21]. The end of the Early Cretaceous was considered the key accumulation period for the Sulige gas field [22].  
The He 8 member, the main producing layer in the northeastern part of Sulige gas field, is 60-80 m thick, and the sandstone is 10-50 m thick, distributed in a north-south band, with a porosity of 5-10% and a permeability of 0.1-0.6 mD. The He 8 member can be further divided into two submembers. Among them, meandering river sediments have developed in the upper submember of He 8, and braided river sediments have developed in the lower submember of He 8; the layer thickness of the Shan 1 member is 40-55 m, which is a set of meandering river sediments [23].  
On the basis of development status, the northeastern part of the Sulige gas field was divided into six blocks (Figure 2). Among them, the gas wells in Areas 4 and 5 in the central part of the study area had the best production and were also the concentrated distribution area of high-yield wells (EUR > 15 million m\({}^{3}\)), with the average EUR of a single well being 11.41 million m\({}^{3}\) and 17.09 million m\({}^{3}\), respectively. The production performance of gas wells in Areas 1 and 6 located on the north and south sides was worse than that in the central area, with average EUR values of 7.86 million cubic meters and 10.2 million cubic meters, respectively. Area 3 is still in the exploration stage and has not yet been commissioned.