## 3 Materials and Methods
### Delta-Front Reservoir Architecture Analysis  
#### 3.2.1 Composite Sand Body Architecture Analysis  
Many methods have been proposed by previous researchers to analyze the subaqueous distributary channel of the delta front. For example, [PERSON] et al. [33] took the Gaoshan 76 fault block of the Nanbao Depression as a case study to analyze the single sand body architecture characteristics in a fault-block small lake basin fan delta front. They summarized four lateral stacking patterns of single sand bodies and the \"river flows over the levee\" model. [PERSON] et al. [34] focused on the Chang 61 layer of the Sai 160 well area in the Anse Oilfield, where they identified the area as a typical meandering river shallow-water delta deposit. The sedimentary microfacies developed in the area included subaqueous distributary channels, delta-front bars, sheet sands, and bay deposits, with the channel deposits being the dominant sedimentary facies, showing a continuous distribution pattern. [PERSON] et al. [8] combined core, well log, and seismic data to perform an architecture analysis of the lower section of the Minghuazhen Formation in the BZ25 Oilfield in Bohai. They explored the sedimentary microfacies composition inside the subaqueous distributary channel and analyzed the macroscopic distribution and internal architecture characteristics of the deltaic bar finger. This study, based on the fine anatomy of the single-channel sand body in the target layer of the research area, summarizes five key boundary identification indicators of single sand bodies: sedimentary facies transitions, top elevation differences, thickness variations, curve morphology differences, and differences in oil and gas potential. 1. Due to differences in depositional topography, the same sand body may bifurcate, resulting in the development of sheet sands or mudstone bands in the middle. Therefore, the presence of mudstone bands or sheet sands often indicates the boundaries of river channels. For instance, sheet sands are observed between wells D236-65 and D237-66, while mudstone appears between wells D237-66 and D238-67 (Figure 4a). Hence, it can be concluded that these represent different river channels. 2. From the elevation difference marker, the top elevation of a single sand body should be consistent, as the sand bodies formed by different subaqueous distributary channels may have differences in elevation due to variations in the depositional paleotopography and developmental periods. If sand bodies are observed at different elevations on a profile, they can be interpreted as deposits from different subaqueous distributary channels. For example, although the sand bodies encountered in wells D241-64 and D240-65 are located in the same single sand layer, their top elevations are inconsistent (Figure 4b), indicating that they belong to different subaqueous distributary channels. 3. The thickness of a single distributary channel sand body decreases from the center towards both sides. If there are differences or abrupt changes in the thickness variations between sand bodies, it is considered that the deposits are not from the same period. For example, wells D239-63, DJ239-641, and DJ237-644 exhibit a trend of thick-thin-thick (Figure 4c), indicating that a boundary between distinct distributary channels exists between them. 4. In terms of logging curve responses, distributary channels from the same depositional period, due to similar material composition and subsequent modifications, show similar logging responses without significant abrupt changes. Moreover, sudden changes in curve amplitude or degree of \"spikiness\" could indicate the presence of boundaries. For instance, the logging curve for well D240-64 is box-shaped, while the logging curve for well DJ239-643 is bell-shaped, showing a noticeable difference (Figure 4d), which indicates a boundary between the two wells. 5.