A 2D mechanical-thermalfluid-dynamical model for geothermal systems at calderas: an application to Campi Flegrei, Italy

A finite difference method has been developed to simulate water flow in a 2D porous medium with boundary conditions specified in terms of pressure and temperature. The method computes steady-state solutions for temperature, pressure and fluid velocities. With an appropriate choice for boundary conditions it is possible to simulate the behaviour of a geothermal system with an incremental pressure and/or temperature applied to a finite part of the base. Pressure and temperature changes produce a change in the fluid flow regime leading to different final temperatures, pressures and fluid velocities (steady state). The method is particularly suitable for simulating the coupled mechanical and thermalfluid-dynamical effects at caldcras, when increases in pressure and heat flow from a magma chamber perturb the conditions of the uppermost aquifer system. Several tests performed with realistic values for the parameters of the porous medium show that increases of pressure at the base are efficiently propagated in the upper medium by water flow, so that the effective centre of overpressure is shifted to considerably shallower levels. This effect can strongly modify the shape of ground deformations at calderas, and strongly amplify the peak values. The proposed method has been applied to the explanation of the very peculiar ground deformation observed at Campi Flegrei during 1982-1984, which showed very high uplifts (1.8 m) and a strong concentration in a small area Q X 3 km(2)). An integrated mechanical-thermalfluid-dynamical model for this caldera is proposed, which could be generalised to other areas. (C) 2001 Elsevier Science B.V. All rights reserved.