Density, (rho), speed of sound, (W), and viscosity, (eta) of natural geothermal fluids from south Russia Geothermal Fields (Dagestan, Caspian seashore) have been measured over the temperature range from (277-353) K at atmospheric pressure. The measurements were made using the Anton Paar DMA4500 densimeter and Stabinger SVM3000 viscodensimeter for four geothermal fluid samples from the various hot-wells Izberbas (No. 68 and 129), Ternair (No. 27T and No. 38T). A sound-speed analyzer (Anton Paar DSA 5000) was used for simultaneously measurement of the speed of sound and density of the same geothermal fluid samples. The average differences between the measured geothermal fluids densities and viscosities and pure water values (IAPWS formulation) are within (0.1-1.77) % and (0.13-2.1) %, respectively, which are considerably higher than their experimental uncertainties. This differences are caused by the high concentrations of some type of ion species, such as (Na+: 7.7 g/l (#38T); Cl-1: 7.7 g/l (#38T); SO4-2 : 0.75 g/l (#68); S+: 0.24 g/l (#68); K+: 0.15 g/l (#27T); Ca+2: 0.074 g/l (#27T); B+: 0.06 g/l (#38T); and Mg+2: 0.033 g/l (#38T)), in the geothermal fluids, which strongly effect on salt concentration dependence of the measured properties. Measured values of density and speed of sound were used to calculate other derived thermodynamic properties such as adiabatic coefficient of bulk compressibility (beta(S)), coefficient of thermal expansion (alpha(p)), thermal pressure coefficient (gamma(V)), isothermal coefficient of bulk compressibility (beta(T)), isochoric heat capacity (C-V), isobaric heat capacity (C-P), enthalpy difference (Delta H), partial pressure derivative of enthalpy (partial derivative H/partial derivative P)(T), and partial derivatives of internal energy (internal pressure) (partial derivative U/partial derivative V)(T), of the geothermal fluid samples. Measured values of density, viscosity, and speed of sound were used to develop correlation models for the temperature and ion species concentration dependences, which reproduced the measured values within 0.03% (density), 2.47% (viscosity), and 0.20% (speed of sound). To confirm the accuracy and predictive capability of the developed correlation models for density, speed of sound, and viscosity, we have applied the models to well-studied binary aqueous salt solutions (H2O + NaCl). The prediction of the density and viscosity of aqueous sodium chloride solutions based on the developed models were very close to their experimental uncertainties (within 0.03% for density and 1.56% for viscosity). The measured properties at atmospheric pressure have been used as a reference data for prediction of the high-pressure thermodynamic behavior. The predictive capability of the model has been checked on reliable experimental data for binary aqueous NaCl solutions at high pressures reported by Kestin and Shankland (1984) and Rogers and Pitzer (1982). The prediction for density and viscosity is within 0.03% and 1.57%, respectively. (C) 2016 Elsevier Ltd. All rights reserved.
