Improved method to determine the molar volume and compositions of the NaCl-H2O-CO2 system inclusion
Tóm tắt
On the basis of Parry’s method (1986), an improved method was established to determine the molar volume (V
m) and compositions (X) of the NaCl-H2O-CO2 (NHC) system inclusion. To use this method, the determination of V
m-X only requires three microthermometric data of a NHC inclusion: partial homogenization temperature
$$(T_{h,CO_2 } )$$
, salinity (S) and total homogenization temperature (T
h). Theoretically, four associated equations are needed containing four unknown parameters:
$$X_{CO_2 } $$
, X
NaCl, V
m and F (volume fraction of CO2 phase in total inclusion when occurring partial homogenization). When they are released, the V
m-X are determined. The former three equations, only correlated with
$$T_{h,CO_2 } $$
, S and F, have simplified expressions:
$$X_{CO_2 } = f_1 (T_{h,CO_2 } ,S,F), X_{NaCl} = f_2 (T_{h,CO_2 } ,S,F), V_m = f_3 (T_{h,CO_2 } ,S,F).$$
The last one is the thermodynamic relationship of
$$X_{CO_2 } $$
, X
NaCl, V
m and T
h:
$$f_4 (X_{CO_2 } ,X_{NaCl} ,V_m ,T_h ) = 0.$$
Since the above four associated equations are complicated, it is necessary to adopt iterative technique to release them. The technique can be described by: (i) Freely input a F value (0⩽F⩽1), with
$$T_{h,CO_2 } $$
and S, into the former three equations. As a result,
$$X_{CO_2 } $$
, X
NaCl and the molar volume value recorded as V
m1 are derived. (ii) Input the
$$X_{CO_2 } $$
and X
NaCl gotten in the step above into the last equation, and another molar volume value recorded as V
m2 is determined. (iii) If V
m1 is unequal to V
m2, the calculation will be restarted from “(i)”. The iteration is completed until V
m1 is equal to V
m2, which means that the four associated equations are released. Compared to Parry’s (1986) solution method, the improved method is more convenient to use, as well as more accurate to determine
$$X_{CO_2 } $$
. It is available for a NHC inlusion whose partial homogenization temperature is higher than clatherate melting temperature and there are no solid salt crystals in the inclusion at partial homogenization.
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