## 3 Materials and Methods
### Delta-Front Reservoir Architecture Analysis
#### 3.2.1 Composite Sand Body Architecture Analysis
Generally speaking, underwater distributary channel sands from the same depositional period, after excluding structural differences, should exhibit similar oil and gas contents. During development, the water flooding characteristics of these sands should also be comparable. If two nearby wells show significant differences in oil and gas content in the same sand body, they can be considered to belong to different depositional periods. For instance, wells DJ237-641 and DJ235-644 encountered water-flooded sands in this layer, while well DJ235-641 interpreted the same layer as an oil-bearing zone (Figure 4e). This indicates the presence of a boundary between the two distributary channels. In the study area, the underwater distributary channel microfacies are well developed. Individual channel sand bodies overlap and cut into each other, forming extensive, continuous thick composite channel sand bodies. Based on the analysis of sedimentary microfacies in each single layer, correlation profiles perpendicular to the sediment source direction  
Figure 4: Boundary identification markers for single sand bodies. were established. Using the five markers for identifying the boundaries of individual channel sand bodies, the boundaries were recognized on the well-to-well profiles. The boundary points were then marked on a planar map to trace the channel flow direction and extent. Profiles parallel to the sediment source direction were used to determine the channel extension distance. Finally, the boundary points were reasonably connected on the planar map to create a distribution map of individual channel sand bodies [35]. Taking the Chang 82-2-1 layer as an example, a hierarchical analysis was conducted from composite channels to individual channels. Figure 5 illustrates the planar distribution of sedimentary microfacies in the Chang 82-2-1 layer, where the composite channel sand bodies display a continuous distribution pattern. By creating horizontal and vertical profiles and applying the five identification markers, channel boundaries were identified. In the CC' profile, well DJ239-643 is interpreted as an oil layer, while D239-65 is a dry layer. Based on the difference in oil and gas content, a channel boundary is identified in this location. Additionally, in well DJ237-664, the natural gamma curve is box-shaped, whereas in D237-66, it is bell-shaped. The difference in logging curve morphology also indicates a channel boundary here. In the DD' profile, the thickness difference between wells D241-65 and D240-66 is minimal, and both wells contain oil-water transition zones. However, the top elevation of D241-65 is significantly higher than D240-66, suggesting a boundary between the two wells. In the vertical profile, wells DJ239-661 and D239-66 are divided into two distinct channels due to thickness differences. Using the above tracking methods, the layer was ultimately subdivided into five individual channels (Figure 5). Among these, the second channel from west to east is the largest, with a width exceeding 500 m and an average thickness of 6.1 m. The westernmost  
Figure 5: Architecture analysis results of the Chang 82-2-1.  
channel is the smallest, with a width of approximately 181 m and a maximum thickness of 9.5 m. The five channels exhibit lateral stacking and overlapping relationships, with only the second channel bifurcating at the lower part, separated by mudstone.