A novel algorithm to estimate mineral elastic properties and pore aspect ratio in the carbonate reservoirs

Abstract

Rock physics models provide a link between the interior structure of rocks and seismic, petrophysics and geological data. Despite considerable advancements in reservoir rock physics, most models are developed to study the sandstone reservoirs, hence their application in the carbonate reservoirs probably needs further discussions. This might be due to the nature of sedimentation, existence of multiple pore types, and the diversity in their packing and sorting. The rock physics models utilizing effective medium theory provide a more accurate estimation by introducing the pore aspect ratio to such methods. However, the pore aspect ratio and the remaining input parameters, including the elastic moduli of minerals, are mostly derived from references and do not necessarily represent the actual rock matrix. In this study an algorithm is provided to simultaneously estimate the bulk and shear moduli of minerals and pore aspect ratio. The algorithm uses the velocity logs along with Kuster-Toksӧz model to derive an equation in terms of mineral elastic moduli and aspect ratio. This equation is then solved using Newton-Raphson method. The results are used to calculate the compressional- and shear- velocities in a carbonate gas reservoir that exhibit a reasonable match with the measured logs with mean absolute errors of 10−4% and 2.97%, respectively. The estimated elastic parameters are then averaged over different lithologies. Application of averaged input parameters resulted in estimation of Vp and Vs with mean absolute errors of 3.54% and 3.88%, respectively. The outcome of this study would also assist on determining the rock forming minerals and the number of pore systems available in the matrix.