This research provides a detailed analysis of the geological structure of the Bajocian and Bathonian deposits at the Kalamkas field based on a newly developed methodological approach for differentiating productive reservoirs by filtration and capacity properties (FCP), using the integrated parameter Flow Zone Indicator (FZI). The use of FZI revealed that, under the conditions examined, it is impossible to clearly delineate the boundaries of different reservoir groups based on the FZI cumulative frequency curve. Therefore, it is proposed that the FZI distribution be considered a sum of separate normal (or lognormal) distributions. Based on this assumption, the overall FZI distribution was processed by identifying local minima. As a result, it was shown that these studied objects are characterized by a complex geological structure driven by high lithological-facies variability, inconsistency in filtration-capacity properties, and thicknesses. Within the productive reservoirs of the Bajocian and Bathonian stages, four different groups of reservoirs were identified, each characterized by its own permeability–porosity correlation relationships. Using the results of grain size analysis of core samples, the authors analyzed the values of FZI and the content of the pelitic fraction. It was found that as the pelitic fraction content increases, the FZI value decreases. A comparison was made between the results of reservoir group identification and the findings from rock sample studies conducted using a scanning electron microscope.