Rock Fracturing Processes Due to Nonlinear Shock Waves in Hot Fluid-Pressurized Domains

Abstract

Recently the attention on hot and pressurised fluid migration in hyperthermal aquifers has been focused on its capability to determine nonlinear deformation of an overlying impervious rock. Bonafede [1] initiated these studies considering a set of nonlinear equations, to interpret the last bradyseismic crisis at Campi Flegrei (Italy) in terms of an ascendant supercritical water, pushed up into the Phlaegrean aquifer by an underlying source considered as snapshot fluid temperature and pressure changes. Thus, by highlighting the importance of the role performed by the ratio of fluid diffusivity versus thermal diffusivity as already stressed by Rice and Cleary [5] and McTigue [2], in 1996 Natale and Salusti [4] found that temperature and pressure disturbances in a one-dimensional formulation could generate thermal and pressure solitary shock waves which propagate throughout the impervious rock with a velocity related to two different phenomena, each with its own velocity. Such propagations were called “B-convection” in the case of very small fluid diffusivity (impervious rocks such as clay or rocksalt), and “N-convection” in the case of higher permeabilities when nonlinear dissipative mechanical effects were not negligible in the energy equation. This last case was successfully applied to Ruhr and Berea sandstones. The general problem is discussed by Merlani, Natale and Salusti [3].