# Source Rock Prediction Using Well Log and Seismic Data:
## 5 Prediction of Source Rock Distribution
### Prediction of Distribution  
In the study area, the degree of exploration is low, few wells are drilled, and most of the areas have no drilling, so the source rock thickness can be predicted using the logging acoustic velocity and seismic velocity. The acoustic time difference data of each well were used to make a compaction model, and the superposition velocity obtained in the study was converted to the root mean square velocity, and the layer velocity was calculated using the Dix formula as follows:  
\[v_{int}=\sqrt{\frac{v_{r,n}^{2}\cdot t_{0,n}-v_{r,n-1}^{2}\cdot t_{0,n-1}}{t_{0,n}-t_{0,n-1}}} \tag{2}\]  
where \(v_{int}\) is layer velocity; \(v_{r,n}\) and \(v_{r,n-1}\) are the root mean square velocity of the \(n\)th and \(n-1\) formation interfaces, respectively, and \(t_{0,n}\) and \(t_{0,n-1}\) are the round-trip travel times of the \(n\)th and \(n-1\) formation interfaces, respectively. Introducing layer velocity into the time-averaged equation can yield the mudstone index:  
\[\frac{1}{v^{\prime}{}_{int}}=\frac{P_{m}}{v_{m}}+\frac{1-P_{m}}{v_{s}} \tag{3}\]  
where \(v_{s}\) and \(v_{m}\) are the velocities of pure sandstone and pure mudstone at the same depth, respectively; \(v^{\prime}{}_{int}\) is the layer velocity at this depth; and \(P_{m}\) is the mudstone index. The thickness of mudstone in the target interval can be calculated using the mudstone index and total formation thickness, which is calculated according to the time-distance relationship:  
\[H_{m}=P_{m}\cdot H_{t} \tag{4}\]  
where \(H_{t}\) is the total thickness of the target interval and \(P_{m}\) is the mudstone index of this layer [48; 49]. On this basis, the effective source rock thickness of the Lower-Cretaceous-Albian-stage in the Cote d'Ivoire Basin can be calculated. For areas in the study area with less or no drilling, the distribution of the source rocks is predicted by converting the sedimentary facies' characteristics into organic facies. Based on the overall TOC content predicted by the total organic carbon method in the initial research, the source rocks are divided into three types of organic facies: good, medium, and poor. The good organic facies have a large area, a high overall abundance of organic matter, and greater hydrocarbon generation potential; locally, it meet the standard of high-quality source rocks. The shallow lake facies of the medium organic facies are mainly distributed in a circumferential pattern around semi-deep-deep lake facies, with a medium level of organic matter abundance and a certain degree of hydrocarbon generation potential. The poor organic facies are mainly river-delta plain sediments, distributed in the outer edge of the basin; for the most part, they are not source rocks (Figure 13). Figure 12: Albian-stage seismic profile of the Côte d’Ivoire Basin. In order to accurately predict the distribution of source rocks, it is necessary to discuss the various characteristics of the source rocks comprehensively [50]. Based on the methods and results mentioned above, the geochemical characteristics, mudstone thickness, and distribution of organic facies are comprehensively analyzed, and the distribution law of the source rocks in the study area is finally obtained (Figure 14). The results show that the Lower-Cretaceous-Albian-stage source rocks in the Cote d'Ivoire Basin have a wide distribution range and have developed in the whole study area. The medium-poor source rocks have mainly developed in shallow lake sediments, which are found in the shelf and uplift areas, with a thickness of about 50-300 m. The high-quality source rocks have widely developed in the semi-deep-deep lake subfacies.