# Estimation of Litho-Fluid Facies Distribution from Zero-Offset Acoustic and Shear Impedances
## 5 Results and Discussion  
The wells were tied to seismic data by check shots of wells \(\times 1\) and \(\times 2\). A constant wavelet was extracted from the wells to achieve the tie between the synthetic logs and seismic traces. Next, three horizons were picked: A, B, and C, which appear as troughs in seismic data, as shown in Figure 6.  
Both the conventional well logs and oil-mud resistivity imager (OMRI) were interpreted at the well (\(\times 1\)) such that the zone of interest extended from 1300 m to 1480 m. Firstly, the sand and shale could be preliminarily discriminated by using the shale volume at the cut-off 0.3. The gas sand and wet sand were differentiated by \(V_{P}/V_{S}\) and water saturation at the cut-offs 2.8 and 0.45, respectively. The thicknesses of the gas sand zones were validated by the net pay thickness mentioned in the well report. Figure 7 shows the OMRI-derived facies against the well-log-derived facies obtained from the petrophysical cut-offs at the well (\(\times 1\)). Both facies logs confirm that the dominant facies is a massive shale that corresponds to the high shale volume and water saturation zones. The massive and planar-laminated sandstone layers correspond to the gas intervals of the two reservoirs: A and B. Those gas zones appear as fining-upward cycles in the shale volume (Vsh) log where \(V_{P}/V_{S}\) and water saturation are low. Minor siltstone zones appear  
in track (a) and coincide with some of the wet sand zones in track (b). The layers become thinner as the depth increases, coinciding with abrupt changes in the well logs. The top of the target zone (1300-1316 m) consists of massive shale, which can be interpreted as a delta plain. The next interval extends from depth 1316 m to 1330 m, where the A reservoir appears as a distributary channel that consists of fining-upward sediments. The top of this interval is considered a fine-grained sandstone, which appears as wet sand in track (b). The rest of the A reservoir consists of equal amounts of the planar and cross-bedded gas-bearing sandstones, where \(V_{P}/V_{S}\), Vsh, and water saturation are low. A sharp contact is clear at the base of the channel at depth 1330 m due to the change from sandstone to shale. Another depositional cycle begins at depth 1330 m, where the massive and laminated shales are interbedded with minor siltstone. The OMRI images show broad and spiral bands in darker clay-rich portions. The shale extends until depth 1422 m, where another  
Figure 6: A seismic section extracted from the near-stack volume and tied to the wells \(\times\)1, \(\times\)2, and \(\times\)3, where the horizons’ tops A, B, and C are in yellow, green, and cyan colors, respectively. Figure 7: Well (\(\times\)) facies and conventional logs: (**a**) OMRI-derived facies, (**b**) well-log-derived facies, (**c**) well logs, and (**d**) well tops. distributary channel appears within the B reservoir. This unit is dominated by massive-to-weakly stratified porous sands. A sharp contact is defined at depth 1438 m, below which the lower interval consists of laminated sandstone with low porosity. The depth interval from 1452 m to 1481 m consists of interbedded sandstone, siltstone, and shale. The reservoir quality in this zone is poor, with high water-saturation and shale-volume. This is matching with the facies log in track (b), where the sandstone is wet. The OMRI images are crucial for data filtering due to their high resolution relative to the conventional well logs. For example, there is a possible streak of coal at depth 1316.8 m which could not be detected by the conventional logs, as shown in Figure 7. Accordingly, all thin layers and coal streaks have been excluded from the facies model. This data preparation step is essential to reduce misclassification. In other words, if the OMRI images are not available, the collected training data cannot be accurate due to the presence of coal streaks and thin layers which are below logging data resolution.