## 5 Sedimentary Facies' Characteristics and Facies' Patterns of Carbonate Rock Section
### Sedimentary Facies' Characterization of Carbonate Rocks
#### 5.1.2 Seismic Phase Characteristics  
In the three-dimensional seismic data, seismic emission characteristics that can reflect sedimentary units such as open platforms, platform margins, and slopes can also be seen. On the cross-section of the convex part of the platform margin phase belt, a relatively obvious flat-bottomed convex hillock reflection shape can be seen. Above the hillock reflection shape, the strata on both sides overlap the convex part [21] (Figure 7). The inside of the hillock reflector shows the characteristics of high frequency, strong amplitude, and high continuity. The phase axis is sub-flat, reflecting that the hydrodynamics in this area are strong and the sediments are obviously multi-layered. These features are consistent with the hydrodynamic characteristics of the sedimentary environment of the platform margin [22]. The frequency and amplitude on both sides are significantly reduced, and the thickness is thinned, reflecting that the water body energy is weak and the sedimentary layering is poor. These features are consistent with the sedimentary environment characteristics of the carbonate slope phase transitioning from the platform margin to the shelf [23]. In addition, the drilling of Well D2 also confirmed that multiple sets of thick layers ofolitic limestone and politic dolomite were developed at the drilling location. The seismic reflection characteristics of this mound-like reflector are significantly different from those of bioherms [24] (Figure 9). In the seismic profile perpendicular to the platform edge phase belt, after flattening the base of the carbonate layer, the seismic reflection characteristics of at least four facies belts are observed (Figure 10). From the appearance, the platform is higher from the D2 well to the southeast. It becomes thinner and extends into a wedge or sheet shape toward the northwest. From the internal reflection structure, the D2 well and its southeast direction show high-frequency, strong-amplitude, and high-continuity sub-parallel layered reflections. There is an obvious bulge near the D2 well, reflecting the sedimentary characteristics of the platform edge to the restricted platform (subtidal zone) in this area [25; 26], while,  
Figure 9: Seismic reflection characteristics’ profile of the slope facies at the edge of the transverse platform (flattened bottom of carbonate strata). to the west of the D2 well and near the DA1 well, the frequency is relatively weakened and the amplitude also becomes medium but the lateral continuity of the reflection axis is good. The overall shape is wedge-shaped or nearly sheet-shaped, with parallel reflections mainly inside, reflecting the environmental characteristics of the carbonate slope [27]; at the DA1 well position, the reflection frequency and amplitude are further reduced and the phase axis is reduced but the continuity is enhanced, showing a sheet-like reflection shape and reflecting the sedimentary environment characteristics of this area close to the open non-marine shelf [28] (Figure 10). From the comparison profile of the connected wells in the region, granular carbonate rocks are mainly developed in the middle and lower parts of the Middle Triassic (T\({}_{2}\)B and T\({}_{2}\)C sections), mainly in the sedimentary environment of a carbonate oolitic beach. They show low gamma values and high resistivity values on the logging curve, with high gamma mudstone interlayers between the two sections. The sedimentary thickness of the Middle Triassic carbonate rocks is relatively stable, ranging from 90-160 m (T\({}_{2}\)B section thickness is 20-60 m, T\({}_{2}\)C section thickness is 70-100 m), and the sedimentary thickness gradually increases from west to east, reaching its maximum thickness in Well D2. The upper part of the Middle Triassic (T\({}_{2}\)A) is mainly composed of high gamma, gray mudstone, which is mainly developed in the sedimentary environment of carbonate slope.