Effect of Heterogeneity Evaluation on Porosity Changes at Reservoir Pressures, Kangan and Dalan Formations, the Central Persian Gulf

Porosity and permeability of reservoir rocks increase due to the significant pressure drop at surface condition, accordingly this leads to overestimation of volume of hydrocarbons in place. In this study, the effect of overburden pressures on the porosity changes of Kangan and Dalan carbonate formations in the central part of the Persian Gulf has been investigated. Porosity and permeability of 111 plug samples were measured at pressures of 14.7, 2200, 3700, 5000 and 5700 psi. Porosity decreases up to 2 % by increasing up to maximum pressure. Samples react to pressure changes differently; and therefore, they justified into various groups. To evaluate the effect of heterogeneity and complete understanding of these reactions, the most acceptable methods of Winland, flow zone indicator, Lucia, porosity and permeability ranges have been used. The changes in porosity against pressure were plotted for each sample and the equation of decreasing the porosity by increasing pressure was defined. The purpose of this study is considering the changes in porosity by increasing the pressures; and therefore, the resulting line slope was considered as an index of changes, and samples with the same slope were considered as similar samples. In other words, if the rate of porosity change versus pressure is similar, the samples have been assumed as similar ones. Afterwards, the coefficient of variation was calculated as the index of line slopes’ dispersion. The results of various rock typing methods indicated that the best methods for evaluating the heterogeneity of porosity change with pressure, are flow zone index, permeability range, Winland and Lucia, respectively.