New Models For Calculations Of Viscosities Of CO₂-Brine System

Geological fluid is the key medium for material migration and energy transfer in the earth's interior.It plays important roles in various geological processes.Metal cations such as Na⁺,K⁺,Ca²⁺,Mg²⁺and anions such as Cl^-,SO₄^2-are the most common ions in geological fluid,and CO₂ is the most important gas component of geological fluid.Understanding of the viscosity of brine containing CO₂ and ions is of great significance to many geological studies such as the geological sequestration of CO₂,the analysis of ore-forming fluid of hydrothermal deposits,the enhanced oil recovery of CO₂ flooding and so on.Modeling is a good way to acquire viscosities of geological fluids within wide P-T ranges.Most of the viscosity models published are either suitable for aqueous solutions containing specific ions or valid within small temperature-pressure ranges,which cannot meet the needs of geological researches.This study developed two models for calculations of viscosities of mixed aqueous electrolyte solutions containing NaCl,KCl,LiCl,NH₄Cl,CaCl₂,BaCl₂,MgCl₂,Na₂SO₄,K₂SO₄ and MgSO₄ based on different methods.?1?The phenomenological viscosity model proposed by Mao-Duan for three binary aqueous electrolyte solutions?LiCl solution,NaCl solution and KCl solution?was extended to binary aqueous electrolyte solutions containing alkali earth metal chloride or sulfates.Then it was coupled with the mixing rule proposed by Hu et al.to predict viscosities of mixed aqueous electrolyte solutions.?2?The Goldsack viscosity model was extended to calculate viscosities of more single electrolyte solutions and mixed electrolyte solutions in a wide temperature-pressure range.Comparisons of calculation of new models with experimental data show that two new models developed by this study not only can represent viscosities of ten binary aqueous electrolyte solutions?including NaCl,KCl,LiCl,NH₄Cl,CaCl₂,BaCl₂,MgCl₂,Na₂SO₄,K₂SO₄ and MgSO₄ solution?over a wide P-T range with high accuracy,but also can predict viscosities of mixed aqueous electrolyte solutions containing these electrolytes.For example,predictions of new models agree well with viscosity data of seawater at temperatures from273 to 373 K,and at pressures from 0 to 140 MPa.In general,the accuracy of first model is a little better than that of the second model.The first model was extended to the aqueous NaCl solution and brine containing dissolved CO₂.Predictions of the model for viscosities of CO₂-NaCl solutions are consistent with experimental data.Variations of the viscosity of CO₂-seawaterwith temperature and pressure were predicted by using the model.Finally,computer software allowing calculations of viscosities of single electrolyte aqueous solution and mixed electrolyte aqueous solutions and CO₂-brine and CO₂-seawater was written for applications.