PROPERTIES OF OILFIELD BRINES - Petroleum Reservoir Fluid Property Correlations - page 155

McGee et al. measured solubility of methane in water and in sodium
chloride brines for various temperatures and pressures. 17 They also
presented a correlation to predict methane solubility as a function
of temperature, pressure, and salinity for temperatures up to 662ºF
(350ºC), pressures to 20,000 psia (137.9 MPa), and salinity to 25 wt%
sodium chloride (5.7 g-mol/kg H 2 O).
In 1992, Duan et al. proposed a method for predicting the solubility
of methane in brines at temperatures from 32ºF to 482ºF (0ºC to
250ºC), pressures from 0 to 23,200 psia (0 to 1,600 bar), and sodium
chloride concentration from 0 to 26 wt% (0 to 6 g-mol/kg H 2 O). 18 Duan
et al. claim that the method is able to predict the solubility of methane in
sodium chloride brine with an estimated uncertainty of 8% throughout
the ranges of temperature, pressure, and sodium chloride concentration
listed above. Duan et al. also presented an equation for estimating the
partial molar volume of methane in brine. Unfortunately, Duan et al.
relied on a large data set presented by Blount et al. that was later found
to contain a systematic error from incorrect data reduction. 19 Blount
and Price published the corrected data in 1982. 20
Spivey et al. developed an empirical correlation to estimate solubility
of methane in sodium chloride brines for temperatures from 68ºF to
680ºF (20ºC to 360ºC), pressures from 130 to 29,000 psia (0.9 to 200
MPa), and salinities from 0 to 26 wt% sodium chloride (0 to 6 g-mol/
kg H 2 O). 21 Unfortunately, the Spivey et al. database used an invalid
conversion for methane solubility for the Blount and Price data set.
In 2006, Duan and Mao updated the earlier Duan et al. correlation
to use the corrected data from Blount and Price, as well as additional
data. 22 They claimed the new model predicted methane solubilities in
sodium chloride brines with an average accuracy of 6% over ranges of
temperature from 32ºF to 482ºF (0ºC to 250ºC), pressure from 14.7
to 29,000 psia (0.1 to 200 MPa), and salinity from 0 to 26 wt% sodium
chloride (0 to 6 g-mol/kg H 2 O).
Although the Duan-Mao correlation gives accurate estimates of
methane solubility, the calculation of the solubility of methane in pure
water using the Duan-Mao method is quite complex. Accordingly, the
authors have modified the Spivey et al. correlation to reflect the corrected
conversion of the Blount and Price data set. The modified correlation
gives accuracy comparable to that of the Duan-Mao method.
Table 4-5 shows the results of the evaluation of correlations for
solubility of methane in pure water and sodium chloride brines.