The Lower Shuaiba Formation is one of the complex carbonate reservoirs in the Middle East that are characterized by extensive textural heterogeneity that corresponds to highly variable reservoir properties. This heterogeneity is related to discrepant depositional settings during the Shuaiba deposition and the digenesis, which had a severe overprint on the original properties. Facies mapping is important to unlock the uncertainties of facies distribution and characterization, highlighting the extent of good quality facies within the reservoir. The key objectives of this study are to capture the lateral distribution of reservoir properties within the Lower Shuaiba in the Musallim Field by identifying facies types and mapping their spatial distribution. The approach used in this study involved a specific workflow that implemented many datasets to capture reservoir heterogeneity and develop a facies model for the Lower Shuaiba in the field. Geological, seismic, petrophysical, well, dynamic, drilling data, and microfacies analysis are all included in the dataset. This work contains a detailed methodology of reservoir rock typing application that is used for predicting the reservoir characteristics of uncored intervals by integrating petrophysics and sedimentology. The final developed maps and models represent the reservoir's internal architecture, highlighting the different expected facies types, their trends, and the expected reservoir quality. The abundance of the Algal-rich characterizes the reservoir in the field area and represents the dominated facies, which cover most of the topmost 10-20 m of the reservoir. The regional depositional setting for the field is a shallow lagoon with restricted open marine input caused by penecontemporaneous buildups. Reservoir quality is primarily governed by diagenesis, not only by facies types. The abundance and arrangement of lithofacies rich in large skeletal allochems, such as the Algal-rich and Rudist-rich dominated lithofacies, play a pivotal role. Dissolution enhancement in these lithofacies fosters more effective connectivity among pores, distinctly surpassing the pore network of the Wackestone-dominated lithofacies. Most connected pores are interpreted as being created by the acidic, aqueous, unsaturated fluids that preceded/or came with hydrocarbon charge time. Depositional heterogeneities, subsequent diagenetic modifications, and structural adjustments have controlled the development and distribution of lateral reservoir properties.