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Resistivity Characterization of Permeability in Microbial Carbonates Onshore Alabama


In carbonate reservoir characterization, permeability is one of the most difficult reservoir properties to estimate and it can be influenced by many factors such as pore structure and pore size, in addition to porosity. Pore structure can greatly affect both the electrical and the hydraulic behavior of the reservoir. The purpose of this study is to investigate the resistivity response of different pore structures in comparison with sonic velocity, for a better understanding of the relations between resistivity, velocity and permeability, in order to map the distribution of potential fluid flow zones. Cementation factor ‘m’ in Archie's law has been found to be related to carbonate pore structure and explains the electrical resistivity variations at a given porosity. In highly heterogeneous carbonates, simple assumption of a default value of m such as 2 for calculation of the hydrocarbon saturation in different pore systems can lead to inaccurate result. In this report, the variation of cementation factor derived from resistivity, density, velocity logs acquired in a carbonate formation onshore Alabama is taken into consideration and investigated to relate to diagenetically generated high permeable zones. Detailed petrophysical analysis of over 8 wells and petrographic analysis of thin sections demonstrate that “m” could be a good indicator of pore structure. From log analysis, we find that the dominant pore type varies from micropore where 1