Theoretical Study of Two-phase Flow through Porous Medium (I)

Fundamental Equations and Some Hydraulic Characteristics of the System

Abstract

Exact equations which describe unsteady distributions of temperature, pressure and saturation in the two-phase flow system in porous medium are derived. Based on the equations, some hydraulic characteristics of the two-phase flow system are investigated. Effects of change in external loads on geothermal state are actually so small that they can be neglected from the equations. Perturbing a quiescent horizontal reservoir by small perturbations, a diffusion equation concerning propagation of pressure change is deduced. Checking up its coefficients, the followings are clarified. (i) The most significant hydraulic storativity (compressibility) of the two-phase flow system is originated from the phase change. (ii) The value of it depends mainly on temperature; from 10¹ bar^-1 at 100°C to 10^-3 bar^-1 at 350°C. Consequently, to elucidate the distribution of underground temperature is very important from the hydraulic point of view. (iii) Heat conduction may affect the propagation of pressure change in the two-phase reservoir of which permeability is 10^-3 darcy in the magnitude and temperature is below 200-250°C.