Provided are techniques for generating and validating facies logs for a horizontal wellbore, including: obtaining facies data for a subsurface formation, including vertical wellbore core data and wireline log data; determining (based on the facies data) a depositional model; determining (based on the facies data) a facies model of a horizontal portion of a wellbore in an target interval of the formation, including a predicted facies log; determining (based on the depositional model) a facies thickness mapping; determining for different locations within the formation (based on a comparison of the predicted facies log and the facies thickness mapping), a discrepancy between the facies of the predicted facies log and the facies thickness mapping for the location; and for locations of a discrepancy, modifying the predicted facies for the location based on the facies indicated for location by the facies thickness mapping, to generate a modified predicted facies log.