Analysis of Vertical Heterogeneity Measures Based on Routine Core Data of Sandstone Reservoirs

Heterogeneous reservoirs are prevalent; otherwise, they are rare. The problem is detecting the degree of such heterogeneity, which has a significant impact on hydrocarbon production in oilfields. Several vertical heterogeneity measures were introduced to accomplish this task. The coefficient of variation (CV), the Dykstra–Parsons coefficient (VDP), and the Lorenz coefficient (LC) are the most common static vertical heterogeneity measures. This study aimed to review these heterogeneity measures, explained how the probability of the permeability distribution affects calculations of heterogeneity measures, explained how involving the porosity affects calculations, and explained how uncertainty in VDP values affects the estimation of cumulative oil production. In this study, 1022 plug core samples from seven wells in different sandstone reservoirs were used. The results reveal that the permeability is log-normally distributed; thus, the CV is calculated based on the variance only. The outliers have a significant effect on the values of the CV. The studied reservoirs are extremely heterogeneous, as evidenced by the VDP. The proposed straight line resulting from the Dykstra–Parsons plot is rarely encountered. Weighting the central points more than the points at the tails gives VDP values similar to those obtained from the data. An uncertainty in the VDP values could have a considerable effect on the calculations of the cumulative oil production. The study also shows that including porosity in the calculation of the LC leads to a decrease in the LC values. The magnitude of the decrease is contingent upon the degree of reservoir heterogeneity and the average porosity. Above LC > 0.7, the reservoir could be extremely heterogeneous.