## 3 Materials and Methods  
### Lithologic Characteristics  
Through detailed observation and description of core data from coring wells in the Daqingzijing area, the rock types are mainly sandstone and mudstone. The sandstone is predominantly composed of gray to gray-black siltstone, argillaceous siltstone, and a small amount of fine sandstone, mainly developed in Sand Groups II-IV (bottom and middle) of the Qing 1 Member. The particles are well-sorted and highly rounded, reflecting good hydrodynamic conditions, primarily formed in channel deposits. Meanwhile, the color of mudstones is one of the most intuitive and significant characteristics, as it can directly reflect the environmental conditions during their formation. For rocks in shallow water, the colors appear light gray, grayish yellow, purple-red, and in oxidized colors; for rocks in deep water, they appear gray, dark gray, gray-black, or black and in other dark shades [21; 22; 23; 24; 25; 26]. The mudstones of the Qing 1 Member are mainly dark in color, being predominantly gray-black or black, indicating a underwater depositional environment (Figure 2). More than 40 core wells were completed in the study area. Based on the direction of the sediment source [27], four long and continuous cores, Hei 62, Hei 68, Hei 57, and Qian144, were selected along a southwest-to-northeast transect. The total core length was 205.8 m. Lithological identification was performed by detailed visual description. The primary rock types at this location include fine sandstone, siltstone, muddy siltstone, silty mudstone, mudstone, and minor Ostracoda-bearing layers. Based on core observations, lithological statistical analysis was conducted. In the Hei62 well, siltstone accounts for 49.03% and mudstone for 36.06%. In Hei 68, the siltstone content is 37.47% and mudstone is 40.82%. In Hei 57, siltstone makes up 17.61%, while mudstone constitutes 57.88%. In Qian-144, siltstone accounts for 16.17%, and mudstone accounts for 66.47% (Figure 3). These four coring wells are located in the study area, occurring sequentially from southwest to northeast. In comparison, it was found that the contents of fine sandstone, argillaceous siltstone, and silty mudstone gradually decline,  
Figure 2: Shale cores in the Qing 1 Member of the Daqingzijing area. while the content of mudstone gradually rises, indicating that the provenance lies to the southwest. As the distance from the provenance direction increases, the hydrodynamic conditions become poorer, and the sand and silt gradually decrease, forming argillaceous sediments dominated by mudstone. Casting thin sections were prepared by vacuum impregnation using blue-dyed epoxy resin. For each core sample, three thin sections were systematically prepared to represent the upper, middle, and lower parts of the interval. Detrital mineral compositions were determined through petrographic analysis. A total of 63 representative casting thin sections were analyzed using point counting, with 350 points counted per sample under an optical polarizing microscope (Leica DFC500, Leica Microsystems, Wetzlar, Germany). This method yielded quantitative data on the mineralogical composition of the rocks. The detrital particle composition in the reservoir is feldspar, rock debris and quartz. The feldspar content is from 28.1% to 64.2%, with an average of 40%. The rock debris content is from 18.8% to 58.4%, with an average of 28%. The quartz content varies between 19.8% and 42.6%, with an average of 32%. The main component type of clastic rocks in the reservoir is lithic feldspar sandstone, with a matrix content of less than 10%. The cement is mainly calcite cement, with a content of less than 15%, as well as a small amount of secondary feldspar enlargement and authigenic quartz cement (Figure 4). In addition, mineralogical composition was analyzed using a D8 ADVANCE X-ray diffractometer (XRD). Prior to experiments, samples were ground into < 200 mesh, and aliquots of 1 g particles were placed into the ceramic tube.