Experimental and modelling study of the solubility of CO2 in various CaCl2 solutions at different temperatures and pressures

Petroleum Science, Oct 2014

Study of the thermodynamic behaviour of CaCl2-H2O-CO2 systems is important in different scientific areas in the chemical and petroleum engineering fields. For example, a system including salt-H2O-CO2 is a common system in CO2 geological storage. During carbonate matrix acidizing, this mixture also appears as the spent acid. Hence, study of the behaviour of this system and the solubility of CO2 in CaCl2 brine in different thermodynamic conditions is critical. In this study, CO2 solubility in 0, 1.90 and 4.80 mol/L CaCl2 solutions at 328.15 to 375.15 K and 68.9 to 206.8 bar were measured. These values are normal for oil reservoirs. A popular thermodynamic model is available in the literature for estimating the CO2 solubility in pure water and NaCl solutions. In this paper, the available model was modified by experimental work to be applicable for CaCl2 as well. Based on the measured data, the component interaction parameters in the base model were adjusted for a CaCl2-H2O-CO2 system. The developed model could predict CO2 solubility in different conditions with remarkable accuracy, particularly for high concentration solutions and at high pressures. This improvement is up to 65% better than in the base model. This model can be used in Darcy scale models for predicting wormhole propagation during carbonate matrix acidizing.

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Experimental and modelling study of the solubility of CO2 in various CaCl2 solutions at different temperatures and pressures

The Journal of Supercritical Fluids. Experimental and modelling study of the solubility of CO in various CaCl solutions at 2 2 different temperatures and pressures Alireza Bastami 1 2 Mohammad Allahgholi 1 2 Peyman Pourafshary 0 1 0 Institute of Petroleum Engineering, School of Chemical Engineering, Faculty of Engineering, University of Tehran, Now with Department of Petroleum and Chemical Engineering, Sultan Qaboos University 1 China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2014 2 Institute of Petroleum Engineering, School of Chemical Engineering, Faculty of Engineering, University of Tehran Study of the thermodynamic behaviour of CaCl2-H2O-CO2 systems is important in different H2O-CO2 is a common system in CO2 also appears as the spent acid. Hence, study of the behaviour of this system and the solubility of CO2 in CaCl2 brine in different thermodynamic conditions is critical. In this study, CO2 solubility in 0, 1.90 and 4.80 mol/L CaCl2 solutions at 328.15 to 375.15 K and 68.9 to 206.8 bar were measured. These values are normal for oil reservoirs. A popular thermodynamic model is available in the literature for estimating the CO2 solubility in pure water and NaCl solutions. In 2 as well. Based on the measured data, the component interaction parameters in the base model were adjusted for a CaCl2-H2O-CO2 system. The developed model could predict CO2 solubility in different conditions improvement is up to 65% better than in the base model. This model can be used in Darcy scale models Solubility of CO2-CaCl2 solubility measurement 1 Introduction In recent years some researchers have been paying attention to environmental issues such as CO2 capture and geological storage in deep saline aquifers or depleted hydrocarbon reservoirs. Consequently, CO2 solubility in pure water and brine has been widely studied. A variety of of CO2 in brine, especially with NaCl, has been accomplished. Since the major salt in aquifers is NaCl, the CO2-H2O-NaCl a limited number of studies of the solubility of CO2 in other electrolyte solutions. A detailed description of the available 2 in different electrolyte solutions is presented by Springer et al (2012). The main purpose of these studies is the estimation of the soluble CO2 mole fraction in pure or saline water. The CaCl2-H2O-CO2 system is a common compositional (HCl) is one of the most common acids used during carbonate 2, water and CaCl2 are produced from the reaction of HCl and calcite. 2HCl+CaCO3 CaCl2 H2O+CO2 Hence, the solubility of CO2 in CaCl2 solutions is carbonate formations. The produced CO2 may remain in the solution in a specific range of temperatures and pressures or may release and form a separate phase which affects 2 can have some effects on the performance of wormholing during carbonate and calcite reaction and retard the reaction between acid and as a retarding agent. On the other hand, the formation of a separate CO2 phase can prevent the movement of the acid of the relative permeability effect between fresh/spent acid and CO2 phases. Hence, formation of a separate CO2 phase can change wormholing performance and also the depth of penetration. There are several methods on different scales for study the mechanism of wormholing and the effect of different parameters on this complicated phenomenon. A comprehensive model is one which properly estimates the predicts the wormholing regime. Darcy models can be used equations of continuity, velocity, concentration and porosity simultaneously. They facilitate the design of an acid job. Nevertheless, the previous Darcy scale models proposed for can be applied together with the above-mentioned equations in acid jobs. Thus, it can be used to improve the accuracy the solubility of CO2 for this case, the models resulting from 2 with some correction factors. The results of a study of CO2 solubility in different ranges of pressure and temperature was reported amount of CO2 much greater than the solubility of CO2 in spent acid in the operational ranges of temperature and pressure. In contrast to the attention paid to NaCl solutions, the number of publications on the CaCl2-H2O-CO2 system is very limited. This is readily apparent in Table 1, where the 2 solubility in CaCl2 solutions by different authors are shown. Scharlin and Cargill (1996) and Springer et al (2012) reviewed the few published studies of the CaCl2-H2O-CO2 (1877), Setchenow (1892), Kobe and Williams (1935), (1993) are not particularly relevant as regards the reservoir conditions owing to low pressure and temperature values. The most significant paper published on CO2 solubility in CaCl2 solutions is that of Prutton and Savage (1945), since the range of temperatures, pressures and salt concentrations important parameters of Darcy scale models. The systems containing CaCl2 studied as widely as NaCl-containing solutions. To calculate conditions. They measured the CO2 solubility in CaCl2 solutions at 348.65, 374.15, 394.15 K and pressures from 15.2 to 709.28 bar. Temperature range, K Pressure range, bar CaCl2 -1 In this paper, the CaCl2-H2O-CO2 system at different ranges of pressure, temperature and CaCl2 molality, which are consistent with reservoir conditions, is studied to measure and model the solubility of CO2 models in Darcy scale. 2 Experiments The purpose of t 2 solubility in different CaCl2 solutions. The temperature and pressure ranges consi as the normal conditions of s 2.1 Materials The purity of CO2 was 99.99%. The anhydrous CaCl2 2.2 Apparatus and procedures Fig. 1 shows a schematic of apparatus used in this study to estimate the solubility of CO2 in CaCl2 solutions. This apparatus is similar to the one used by Bando et al (2003) and cm3/h in constant pressure mode, a high pressure cylinder with a volume of 500 cm3 of 689 bar, a stainless steel pycnometer, high pressure transfer and 0.1 K precision, a pressure transducer for the 1-620 bar range with 0.007 bar precision, a densitometer, and a vacuum pump. An agitating pump system as shown in Fig. 2 was designed to agitate the high pressure cylinder in the oven. The First of all, the high pressure cylinder was opened and washed with distilled water and evacuated by a vacuum pump. CaCl2 solution and CO2 were then pumped into agitated at the desired temperature for 3 hours. The effects of agitating time were investigated for 1.9 mol/L CaCl2 solution at 137.9 bar and 351.65 K (Fig. 3). In this study, the soluble CO2 mole fraction changed negligibly for data acquired in ensure equilibrium, the samples were agitated for 3 hours. As the pressure changed during the agitating period, the pressure was adjusted again. The concentration of the injected CO2 was more than its saturation concentration to ensure reaching the saturation concentration of CO2 in solution. Thus, there was a separate supercritical CO2 phase in the high pressure cylinder after reaching equilibrium. Since the high pressure cylinder had was transferred gradually through lines to a pycnometer. W 1) at the final temperature and pressure. Knowing the weight of the evacuated pycnometer (W0) and its volume means that we can determine the solution density. To determine the amount of CO2 dissolved in this solution, the pycnometer must be aged for 1 hour under room conditions to reach room temperature. Then, the pycnometer valve was opened and the gas was released slowly from the top of the pycnometer until no more gas was released and the weight of the cylinder did not change. Immediately, the pycnometer valve was closed to maintain the gas phase equilibrium. Finally, the pycnometer with the remaining solution was weighed (W2). All of the The total volume of soluble CO2 consisted of the CO2 released in the gas phase when the temperature and pressure were reduced to atmospheric conditions (VC(1O)2), CO2 remaining in the gas phase in the pycnometer after its valve was opened (VC(O2)2), and CO2 remaining in the liquid phase at atmospheric presTshueredainffderreonocme tbeemtwpeeerantuWre1 (aVnCd(O3)2 W).2 is the amount of CO2 in the gas phase which is released while the valve of the pycnometer is being opened. Hence, where CO2 is the CO2 density, g/cm3 brine is the CaCl2 brine density, g/cm V cylinder is the volume of the pycnometer, cm3. 3 To estimate the CO2 solubility, it is required to estimate the amount of soluble CO2 in CaCl2 solutions at atmospheric pressure and room temperature. With reference to the method CO2 in aqueous electrolyte solutions can be estimated by the log L0 L L VG VL VL A and B are empirical constants dependent upon the particular solute present, as shown in Table 2, L/mol. These constants were different electrolyte solutions such as CaCl2-H2O using the method of least squares. (1) (2) (3) (4) (5) (6) (7) VCO2 The absolute value of soluble CO2 volume in solution is then calculated from Eq. (8). The CO2 solubility in terms of molality is then given by by VCO2 22.414Wwater , in which Wwater can be calculated by Wwater Wbrine 1 (9) 2 soluble in the solution (8) (10) can be calculated by Eq. (10): xCO2 mCO2 mCO2 where xCO2 is the total mole fraction of CO2 mCO2 is the molality of CO2 in the liquid phase, mol/L. 2.3 Experimental results pure water are listed in Table 3 and also depicted in Fig. 4. study at different temperatures. Koschel et al (2006) measured the CO2 solubility in pure water at 323.15 K and 373.15 K not the same, this comparison confirms the accuracy of the study are listed in Tables 4 and 5. These data show the trend of changes in CO2 solubility in solution with changing pressure and temperature. 0.025 n0.020 o it c a r fe0.015 l o m O20.010 C These data indicate that at low pressures the solubility of CO2 in CaCl2 solutions increased directly with pressure. At high pressures, however, the effect of pressure on CO2 solubility faded and the rate of increase in CO2 solubility reduced with an increase in pressure. This observation was et al, 2012). On the other hand, the temperature and CaCl2 concentrations had inverse effects on CO2 solubility. 3 Model development The solubility of CO2 in pure water and brine at reservoir for conditions up to 373.15 K and 1,000 bar, by Duan and Sun (2003) for conditions up to 533.15 K and 2,000 bar and K and 600 bar. Duan and Sun (2003) presented a popular thermodynamic model for the estimation of CO2 solubility in pure water and aqueous NaCl solutions. They stated, however, is possible to use it to predict CO2 solubility in other systems as well. The method of CO2 solubility estimation proposed by Duan and Sun (2003) is based on the balance between chemical potentials between CO2 in liquid and gas phases. This balance results in Eq. (11). 0.07mSO42 (11) P ln mCO2 2 CO2 -Na ln yCO2 CO2 P mNa mK CO2 -Na-ClmCl mNa 2mCa mK l(0) CO2 RT 2mMg mMg mCa where yCO2 is the mole fraction of CO2 and R is the universal gas constant, 0.08314 bar·L·mol-1·K-1 T is the chemical potential and mSO42 is the molality of SO42- in the liquid phase (if any), mol/L. 2H2O-NaCl system in the conditions of the study, it is assumed that the water vapor pressure of H2 to the pure water saturation pressure. Based on the study of Duan and Sun (2003), this assumption may lead to errors (up to 5%) for Cl(O02) RT . They stated that these errors have a negligible effect on the calculation of CO2 solubility. Thus, yCO2 can be calculated by yCO2 P PH2O P . Duan and Sun suggested an empirical equation for calculating PH2O as: P PcT Tc where c is the critical pressure of water, Pc Tc is the critical temperature of water, Tc PH2O is the t T Tc Tc and the parameters of Eq. (12), c1-c5, are listed in Table 6. Duan et al (1992) also developed an equation of state for supercritical CO2, as in Eq. (13). Value predicting the CO2 solubility in CaCl2-H2O system. They concluded that the model developed by the interaction parameters for NaCl solutions, can be applied for CaCl2 solutions as well. The parameters ’s and ,s for Na+ and Cl and also the standard chemical potential of CO2 in the liquid phase are essential to calculate the CO2 solubility as a function of temperature, pressure and salinity. On the other hand, measurements can only be made in electrically neutral To calculate Vr, the reduced temperature and pressure should be calculated and substituted in the EOS developed by Duan et al (1992) as in Eq. (13). The parameters of Eq. (13) are listed in Table 7. interaction parameters are estimated by Eq. (14), with the constants listed in Table 8. Par T , P c6 P c2T c8 P T c3 T c9 P c4T 2 630 c5 T T 2 and the data reported by Prutton and Savage (1945), the interaction parameters of Duan and Sun’s solubility model are modified for CaCl2 solutions. The constants of Eq. (14) CO2 -Ca and CO2 -Ca-Cl , in comparison with the ones presented by Duan and Sun (2003) for NaCl solutions, are shown in Table 9. As can be seen from the table, Cl(O02) RT is not changed, because it is independent of the solvent in the solution. n RMSE x1,t x2,t 2 n (15) 4 Results and discussion T h e m o d e l p r o p o s e d b y D u a n a n d S u n ( 2 0 0 3 ) overestimates the CO2 solubility in high molality solutions and also at high pressures as well. This observation was and Hilal, 2010). A comparison between the CO2 solubility estimation by the base and modified models has been L CaCl2 solutions. The model is more accurate for higher concentration of CaCl2 and higher pressures as well. L solutions is reduced. Hence, the developed model is more accurate. The comparison between CO2 mole fractions is illustrated in Fig. 5. CO2 solubility estimations for the 1.90 mol/L CaCl2 seen in Fig. 5 for 4.80 mol/L CaCl2 solutions, however. This indicates that this improvement has more meaning for high concentrations of CaCl2 solutions. Prutton and Savage (1945) proves that predictions of the new All plots of Fig. 6 show this improvement for different values of temperature, pressure and CaCl2 concentrations. 2 solubility estimations are reduced by about 14%, 53% and 65% on the basis of the Prutton and Savage (1945) results for 1.01, 2.28 and 3.90 mol/L CaCl2 have been improved about 25% for 4.80 mol/L CaCl2 be concluded that the modified model shows a significant as well. Fig. 6 shows a comparison between data estimated (c) T= 368.15 K (a) T=328.15 K 80 100 (b) T=348.15 K Fig. 6 improvement in CO2 mole fraction estimations. The model presents better results for high concentration solutions. reduction, but that for the 1.90 mol/L solution is almost unchanged. CO2 mole fraction in CaCl2 solutions in better agreement with increase with pressure, temperature and CaCl2 molality. Adding more CaCl2 to the solution results in decreasing CO2 solubility within the system. The base model cannot match T=348.15 K, 1.01 mol/L CaCl2 T=373.15 K, 1.01 mol/L CaCl2 T=393.15 K, 1.01 mol/L CaCl2 Experimental Modified Duan model Duan model Experimental Modified Duan model Duan model 8.0E-04 6.0E-04 SE 4.0E-04 M R 2.0E-04 0.0E+04 2 solubility based on data from Prutton and Savage (1945) Duan model Modified Duan model this behaviour, but the new developed model can predict the behaviour of the system more precisely. This comparison 2 solubility prediction in 3.90 mol/L CaCl2 solutions compared with the Duan model, as shown in Fig. 6. Since the range of CaCl2 concentrations in this study is improvement in estimating the soluble CO2 mole fraction is noteworthy in wormhole propagation models. The original form of the Duan model overestimates CO2 solubility in spent presented in this study gives more reasonable estimates of CO2 solubility in spent acid. This solubility model can be used in an integrated study on wormhole propagation during 5 Conclusions 1) The solubility of CO2 in saline water is of particular importance regarding environmental issues such as CO2 capture and geological storage. Hence, the thermodynamic behavior of CO2-H2 contrast, CO2-H2O-CaCl2 has only been studied to a limited CO2 in CaCl2 solutions. was prepared and the solubility of CO2 in 0, 1.90 and 4.80 mol/L CaCl2 solutions at 328.15 to 375.15 K and 68.9 to 206.8 that CO2 solubility decreases with increasing concentration, increasing temperature and decreasing pressure. The effect of pressure, however, diminishes at higher pressures. 3) A modified model was developed by refitting the interaction parameters to predict the CO2 solubility in CaCl2 solutions. The modified model can predict solubility better than the available Duan and Sun thermodynamic model. This improvement is up to 65% better than the Duan and Sun model. In addition, the modified model estimates the CO2 solubility in high concentration solutions and also high pressures with noticeable accuracy. Prediction by this model this study. 4) Darcy models on the basis of core scale predict In the course of reactions between acid and carbonates CO2 physically affect the performance of an acid job, it is of 2 is not soluble in the solution (spent acid) and can form a separate study can be applied in Darcy scale wormhole propagation models to improve the accuracy of their predictions. 2005. 51(12): 3231-3248 and acid-fracture conductivity. SPE Production & Operations. 2013. 28(1): 46-54 (paper SPE 136217) 1981. 33(7): 1196-1202 (paper SPE 9388) 2 in aqueous 1477 H2O-rich to the CO2 151-171 Spycher N and Pruess K. CO2-H2 sequestration of CO2 CO2-H2 Chemical & Engineering Data. 2003. 48(3): 576-579 Darwish N A and Hilal N. A simple model for the prediction of CO2 solubility in H2O-NaCl system at geological sequestration conditions. Desalination. 2010. 260(1-3): 114-118


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Alireza Bastami, Mohammad Allahgholi, Peyman Pourafshary. Experimental and modelling study of the solubility of CO2 in various CaCl2 solutions at different temperatures and pressures, Petroleum Science, 2014, 569-577, DOI: 10.1007/s12182-014-0373-1