Improved method to determine the molar volume and compositions of the NaCl-H2O-CO2 system inclusion

Science in China Series D: Earth Sciences - Tập 50 - Trang 385-391 - 2007
YuCai Song1, WenXuan Hu1, Pei Ni1, ZhenHao Duan2, XueFeng Zhang1
1State Key Laboratory of Mineral Deposit Research, Department of Earth Sciences, Nanjing University, Nanjing, China
2Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

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.

Tài liệu tham khảo

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