PROPERTIES OF OILFIELD BRINES - Petroleum Reservoir Fluid Property Correlations - page 160

Computing Properties of Oilfield Brines
The modified Spivey et al. correlations are recommended for calcu-
lating properties of oilfield brines. This section shows how to calculate
properties of oilfield brines using the recommended correlations.
Units. Spivey et al. used metric units in developing their brine density
and methane solubility correlations. For all of the equations in this
section (unless otherwise noted) temperature, T , is in ºC, pressure, p ,
is in MPa, and salinity (sodium chloride concentration), m , is in g-mol/
kg H 2 O. (For clarity, the salinity is explicitly denoted with a subscript,
m NaCl , in equations for brine containing dissolved methane.) Density,
ρ , is in g/cm 3 ; specific volume, v , is in cm 3 /g; compressibility, c w , is in
MPa -1 ; and methane solubility, m CH4 , is in g-mol/kg H 2 O. Formation
volume factor, B w , is in cm 3 /cm 3 , and solution gas-water ratio, R sw , is in
cm 3 /cm 3 . Unit conversions between metric and oilfield units are given in
a separate section below.
For most quantities, the subscripts w and b indicate properties
of pure water and brine, respectively. Because of long-established
practice, the superscript w is also used for certain properties of oilfield
brines of particular interest in the oilfield. These properties include
compressibility [equations (4.32) and (4.35)], formation volume factor
[equation (4.36)], and solution gas-water ratio [equation (4.37)].
Temperature-dependent coefficients. In developing the brine density,
brine compressibility, and methane solubility in brine correlations,
Spivey et al. used a rational function in temperature, of the form
(4.1)
as a general correlation equation for temperature-dependent parameters.
The coefficients a i for use in equation (4.1) are tabulated below for
various temperature-dependent parameters.