Interrelationships of Rock Elastics Properties to Petrophysical Pore Structure and Geometric Details of Sandstone

Abstract

Abstract This paper presents new interrelationships of elastic properties of the porous rock to petrophysical parameters in order to enhance better understanding on how compressional and shear waves velocities, young modulus, bulk modulus, lame’s coefficients, and Poisson’s ratio correlate with permeability, porosity, petrophysical geometric details of the pore system, and microscopic geological features. This study employs 215 sandstone core-plugs from North West Java Basin. The approach used utilizes the Kozeny-Carman equation with Re-arrangement made on this equation leads to rock typing based on pore structure similarity, similar in pore shape factor and tortuosity. By plotting pore geometry against pore structure variable, it shows that P- and S-wave velocities, young modulus, bulk modulus, Poisson’s ratio, and lame’s coefficients data can be clearly grouped based on rock type and have strong correlations with permeability, pore geometry, and pore structure parameters. This grouping method enables to investigate the main influential factors that systematically control rock elastic properties. The interrelationships of each parameter of P-wave and S-wave velocities, young modulus, bulk modulus, Poisson’s ratio, and lame’s coefficients versus pore geometry and pore structure were constructed. The critical finding is that each relation among the rock groups of each elastic property is clearly separated. Each rock type has a similar pattern in that P-wave and S-wave velocities increase with pore geometry and pore structure variables. These velocities tend to be high with an increase in Kozeny constant. However, for a given porosity for all the groups, these velocities increase remarkably with a decrease in Kozeny constant. In other word, velocities increase with either an increase in the complexity of pore systems or, at the same pore complexity, a decrease in specific internal surface area. In addition, young modulus, bulk modulus, and lame’s coefficients also increase with pore geometry and pore structure in each rock type. As a novelty, this study helps to characterize the elastic properties based on porosity and permeability data in the form of pore geometry and pore structure. Furthermore, this work can help us to predict some elastic properties at in-situ condition as long as we have the porosity and permeability values interval.