## 5 Applications and Discussion  
### Geological and Geophysical Characteristics  
During the Paleogene sedimentary period of the lower E\({}_{3}\)d\({}_{2}\) Formation in the HHK Depression, the study area was situated within a lacustrine transgressive system tract (TST) characterized by braided-river delta-bar depositional systems. Quantitative analysis of individual sandbody dimensions (thickness and frequency) reveals that the thin-bedded beach-bar facies in the lower Ed\({}_{2}\) Formation predominantly consist of gray, fine-grained feldspathic litharenite, lithic feldspathic sandstone, feldspathic sandstone, and litharenite, with localized siltstone interbeds (Figure 10a). The lower Ed\({}_{2}\) member of the Paleogene succession in the study area exhibits a distinctive stratigraphic architecture character ized by thin-bedded sandstone packages intercalated within thick mudstone sequences (Figure 10a). Individual sandstone beds range from 3 to 8 m in thickness, typically comprising 1-2 discrete layers vertically separated by mudstone intervals exceeding 100 m in cumulative thickness. This vertical stacking pattern manifests a \"thin-bedded sandstone-thick mudstone\" alternation, indicative of low accommodation/sediment supply conditions.  
The quartz content within the sand bodies ranges from 29.0% to 46.0% (average: 36.2%), while feldspar content varies from 29.0% to 41.0% (average: 34.8%). The proportion of lithic fragments falls between 25.0% and 33.0% (average: 29.75%). The cumulative probability curve exhibits a segmented pattern of two to three segments, with an average particle size (Mz) of 0.474 mm and a skewness (Sk) of 0.922. The saltation fraction content ranges from 30% to 50%, while the suspension fraction content exceeds 50%. The phi (\(\phi\)) value at the intersection between the saltation and suspension fractions ranges from 2.5 to 3.5, indicating that the fine cutoff point skews toward finer sizes. This suggests a reduced proportion of the saltation fraction and a greater overall content of suspension, indicative of pronounced suspension sedimentation and wave action (Figure 10b). The sorting of particles is classified as good to moderate, while the roundness ranges from moderate to sub-rounded, with grains primarily exhibiting point-to-line contacts (Figure 10c).  
Thick-layered beach-bar sand bodies typically display natural potential (SP) and natural gamma (GR) curves characterized by large amplitude and exhibiting funnel-shaped or boxy profiles. Conversely, thin-layered beach-bar sand bodies present natural potential (SP) curves with medium to low amplitudes, displaying finger-like profiles, while the  
Figure 10: Geological and Geophysical characteristics of the Lower E\({}_{\textrm{5}}\)d\({}_{\textrm{2}}\) Sub-member in HHK Depression. (**a**) Sandstone, reverse sequence, C4-2-a, 3167–3168 m; (**b**) Three-segmented structure, C4-4-e (3043 m), C4-4-a (2850.1 m), C4-4-a (2887.7 m); (**c**) Fine-grained lithic feldspathic sandstone, cast thin section, C4-6-a, 3167.43 m; (**d**) Funnel-shaped, finger-shaped, box-shaped, and box-leak composite structures, C4-1-a; (**e**) Parallel-to-subparallel strong seismic reflections.  
natural gamma (GR) curves reveal a fine-toothed, finger-like configuration (Figure 10d). The seismic facies of the beach-bar deposits within the study area are characterized by moderate to good continuity, with parallel to subparallel reflector configurations and medium to strong amplitude reflections. Thicker sand bodies exhibit seismic facies distinguished by high continuity and strong amplitude reflections, whereas thinner sand bodies demonstrate seismic facies characterized by moderate continuity and medium strength amplitude reflections (Figure 10e).