Rock-physics model of volcanic rocks, an example from Junggar Basin of China

Abstract

A variety of resources such as geothermal, mineral, groundwater, oil and gas, etc., are explored in the volcanic rock reservoirs, which has aroused widespread focus in the world. The researches on the relationship between macroscopic physical properties and microstructures are conducive to the resource exploration and development, in which the rock-physics model is an important and valid media. Taking the Junggar Basin in Western China as an example, a novel rock-physics model for volcanic rocks is proposed. The mineral contents are initially estimated with the proposed evolutionary complex algorithm based on a novel volume interpretation model suitable for the diversity of the minerals of different lithology. The simultaneous inversion of the porosity and aspect ratio of different kinds of pores constrained by the P-wave and S-wave velocities is further implemented and then the heterogeneity of the rock can be carved. In addition, to satisfy the hypothesis of the fluid saturation model, the disconnected pores including bound water and invalid pass are introduced by the acoustic porosity formula as a part of the matrix. Furthermore, due to the approximate aligned cracks, the volcanic rock reservoirs can be simplified as transversely isotropic media with horizontal symmetry axis. The Eshelby-Cheng model and Brown-Korringa theory are further utilized for the estimation of the elastic modulus of the anisotropic dry rock and saturated rock, respectively. The example demonstrates that the proposed rock-physics model is able to predict the elastic parameters of different lithology of volcanic rocks and the modelling method can give some enlightenment for the exploration of other volcanic resources.