The characterization of formation heterogeneities requires a multidisciplinary study of data acquired using a large number of numerical geophysical and geological measurements, and a rigorous evaluation of the precision and accuracy of the data. In this work, an Interactive Non-Hierarchical Cluster Analysis (INCA) is used to identify heterogeneities in complex formations and to evaluate the boundaries they generate. Examples from two Ocean Drilling Program (ODP) holes were used to show the characterization obtained with this technique. In addition to the characterization, the quality control and quality assessment of the well log data used in this work is achieved through the use of a parameter (6) to rate the importance of each log curve during the characterization. It also allows the assessment of how difficult the boundaries are distinguished from each other.