Fracturing processes due to temperature and pressure nonlinear waves propagating in fluid‐saturated porous rocks

Abstract

Abstract. A model is proposed of rock deformation-fracturing in the subsurface of hydrothermal systems in response to deep fluid-rock temperature and pore fluid pressure perturbations, carried upward by hot and pressurized fluid fronts. Since during these episodes of unrest one also has to take into account that rock parameters can evolve, a model of fluid diffusivity change as a function of pore fluid pressure is described. Through reformulating the linear thermoporoelastic equations, rock deformation-fracturing is thus thought of as being associated with migration of thermomechanical nonlinear waves, which travel upward, associated with an increase in concurrent fluid diffusivity. On dynamical grounds it is assumed that on the boundary of the two superimposed horizons the overlying rock suddenly starts rupturing, caused by the arrival of supercritical water from below, which drives up a pore fluid pressure excess. In this connection, the purpose of this analysis is to investigate the general evolution of the subsurface pressure and temperature fields, assuming that the original signal is itself strong enough to generate fracturing processes of the overburden rock on its arrival. A general formulation provides evidence of nonlinear "thermal waves," "compensated waves," and "residual pressure Burgers waves," that can be found for every value of the system parameters. A mechanical analogy is also presented, which is treated analytically and numerically, allowing one to gain intuitive insight into such complex phenomena. A characteristic of these nonlinear processes is that the resulting timescales (of the order of years for the case of the Campi Flegrei and the Izu Peninsula) can be particularly small, corresponding to quick hyperthermal phenomena during the flitrating movement of fluid toward the Earth's surface.

Localization of self‐potential sources in volcano‐electric effect with complex continuous wavelet transform and electrical tomography methods for an active volcano

“…In this study, we assume that an active volcanic system is principally controlled by two phenomena: the coupling between magmatic intrusion and thermo‐hydro‐mechanical (THM) disturbances [ Natale , 1998; Merlani et al , 2001], and the electromagnetic field induced by the current density. This latter is generated by the circulation of a fluid flow in the porous formation [ Mitzutani et al , 1976; Michel and Zlotnicki , 1998; Yoshida , 2001; Revil et al , 2003], increased here by the THM process (e.g., variation of the strain or temperature field).…”

The volcano‐electric effect

“…Several types of THM effects can coexist in a volcanic system. For example, Merlani et al [2001] investigated a model of rock fracturing in the subsurface of hydrothermal systems in response to temperature and pore fluid pressure perturbations. In such conditions, thermoporoelastic theory predicts the upsurge of hot and pressurized fluid fronts, which take the form of nonlinear thermomechanical and mechanical wave solutions of two Bürgers equations.…”

Role of permeability and storage in the initiation and propagation of natural hydraulic fractures

“…Consideration of the time dependence of fluid flow may aid in understanding the temporal and spatial evolution of fault and damage zones. In addition, problems of fracturing in hot and pressurized hyperthermal aquifers [Natale et al, 1998;McTigue, 1986;Merlani et al, 2001;Natale and Salusti, 1996] may be addressed by models similar to those we have developed.…”