Page 279 - Geothermal Energy Systems Exploration, Development, and Utilization

5.3 Reservoir Characterization 255

25% salinity Viscosity
(Pa s)

25% salinity 0.0030
Density
3
(kg/m ) 0.0025
1000 0.0020

800 0.0015

600 0% salinity 0.0010

400
200 0% salinity 0.005
200 400
400 0
100 P (bar) 600
600 0
200 100
800 T (°C) 200
P (bar) 300 300
1000 T (°C)
(a) (b)
Figure 5.5 Variable hydromechanical fluid properties, den-
sity (a), viscosity (b) (McDermott et al., 2006).
The equation of state for the fluid density (Equation 5.17) is related to reference
temperature, reference pressure, and reference concentration.

l
ρ = ρ l 1 − β T (T − T 0 ) + β p (p − p 0 ) + β C (C − C 0 ) (5.17)
0
C s − C 0
Therefore, the flow and transport equations for thermohaline convection are
nonlinear and strongly coupled since temperature, pressure, and salinity control
the fluid density.

5.3.2.2 Heat Capacity and Thermal Conductivity
Not only viscosity and density, also thermal fluid properties depend on temperature
and salinity changes (Figure 5.6).
The functional relation for rock thermal conductivity is given by Somerton (1992).

−3
λ(T) = λ 20 − 10 (T − 293)(λ 20 − 1.38)
−3 −0.64
× λ 20 (1.8 × 10 T) −0.25λ 20 + 1.28 λ (5.18)
20
◦
where the suffix 20 denotes the heat conductivity measured at 20 C by laboratory
experiments. By means of Equation (5.18) it is possible to calculate the heat
conductivity of the solid at any point of the reservoir with defined temperature.