nvestigating the Heterogeneity of Porosity and Permeability of Darian Formation using Heterogeneity Logs in One of the Central Persian Gulf Fields

Quantitative heterogeneity presentation is very important to compare the amount of heterogeneity in different reservoir characteristics in carbonate reservoirs. The aim of the present study is to quantify the heterogeneity by calculating the heterogeneity log and its application in investigating the heterogeneity of porosity and permeability in the Late Barremian-Early Aptian Darian carbonate Formation in the central part of the Persian Gulf. In order to calculate the heterogeneity logs, the well log data of gamma ray, bulk density, neutron porosity, acoustic and deep resistivity and the statistical methods of Lorenz coefficient and coefficient of variation have been used. Results show that the calculation of the heterogeneity log provides the possibility of quantitative comparison of the heterogeneity between different parts of the reservoir for different purposes. Heterogeneity calculation with both methods is efficient for calculating heterogeneity, but it should be noted that the coefficient of variation for the maximum heterogeneity does not have a specific range like the Lorenz coefficient. Also, increase in porosity is associated with a decrease in the amount of heterogeneity in the heterogeneity logs of deep resistivity, acoustic, neutron porosity and density. Unlike other logs, gamma ray heterogeneity log has little direct relationship with porosity in Darian Formation. Two types of neutron porosity heterogeneity and deep resistivity are the most used in determining the reservoir properties in this formation. Permeability shows a weak relationship with heterogeneity logs. In bioclast wackestone microfacies of carbonated units with high porosity, less heterogeneity is observed. Also, units with higher porosity are thicker and therefore exert stronger mean effects on heterogeneous areas. High variability in porosity and permeability causes higher heterogeneity. This is also the case about lithology and clay minerals. Heterogeneity changes at facies change boundaries. Therefore, heterogeneity log can be used to investigate geological heterogeneity, porosity, permeability and reservoir zoning.