Secondary porosity classification in heterogeneous carbonate reservoirs based on the sonic log data

Abstract

Many carbonate oil and gas reservoirs are characterized by the presence of secondary pores: vugs and fractures. To estimate the volume of oil and gas in carbonate rocks with double porosity, the information about secondary pore structure is required. In the present work we propose a simple and easy to code methodology to determine secondary pore types in carbonate sediments using acoustic well log data. The methodology is based on the comparison of the normalized differences between the calculated and measured in a borehole velocity of the compressional and shear waves. The results were obtained for the rocks with polymineral skeleton (limestone and dolomite). The mineral concentration is estimated by the solution of the inverse problem using the data obtained by a neutron, density, and PEF logging. The classification results were adjusted by using the micromechanical methods (the Kuster-Toksöz method and the Effective Medium Approximation (EMA)). Examples of the developed methodology application in the carbonate reservoirs are presented.