Surfactant-enhanced aquifer remediation is often performed to overcome the capillary forces that ... more Surfactant-enhanced aquifer remediation is often performed to overcome the capillary forces that keep residual NAPL phases trapped within contaminated aquifers. The surfactant selection and displacement mechanism usually depend on the nature of NAPL constituents. For example, micellar solubilization is often used to cleanup DNAPLs from aquifers whereas mobilization is desirable in aquifers contaminated by LNAPLs. Although the majority of crude oils are LNAPLs, they often contain heavy organic macromolecules such as asphaltenes that are classified as DNAPLs. Asphaltenes contain surface-active components that tend to adsorb on rocks, altering their wettability. Previous studies revealed that surfactants that formed Winsor type III microemulsions could promote both mobilization and solubilization. However the extent by which these two mechanisms occur is still unclear, particularly in oil-contaminated aquifers. In this study we investigated the remediation of oil-contaminated aquifers using an environmentally friendly surfactant such as n-Dodecyl β-D-maltoside. Focus was given on asphaltenes to better understand the mechanisms of surfactant cleanup. Through phase behavior, spontaneous imbibition, dynamic interfacial tension and contact angle measurements, we showed that microemulsions formed by this surfactant are able to mobilize bulk NAPL (containing 9wt.% asphaltenes) in the porous rock and solubilize DNAPL (i.e., 4-6wt.% adsorbed asphaltenes) from the rock surface. Spontaneous imbibition tests, in particular, indicated that the ratio of mobilized to solubilized NAPL is about 6:1. Furthermore, aging the cores in NAPL beyond 3days allowed for more NAPL to be trapped in the large pores of the rock but did not alter the amount of asphaltenes adsorbed on the mineral surface.
The safe trapping of carbon dioxide (CO 2) in deep saline aquifers is one of the major concerns o... more The safe trapping of carbon dioxide (CO 2) in deep saline aquifers is one of the major concerns of CO 2 sequestration. The amount of capillary trapping is dominated by the capillary pressure of water and CO 2 inside the reservoir, which in turn is controlled by the interfacial tension (IFT) and the contact angle (CA) of CO 2 /water/rock systems. The measurement of IFT and CA could be very challenging at reservoir conditions, especially in the presence of toxic cocontaminants. Thus, the ability to accurately predict these interfacial properties at reservoir conditions is very advantageous. Although the majority of existing molecular dynamics (MD) studies of CO 2 /water/mineral systems were able to capture the trends in IFT and CA variations with pressure and temperature, their predictions often deviated from experimental data, possibly due to erroneous models and/or overlooked chemical reactions. The objective of this study was to improve the MD predictions of IFT and CA of CO 2 / water/quartz systems at various pressure and temperature conditions by (i) considering the chemical reactions between CO 2 and water and (ii) using a new molecular model for α-quartz surface. The results showed that the presence of carbonic acid at the CO 2 /water interface improved the predictions of IFT, especially at low temperature and high pressure where more CO 2 dissolution occurs. On the other hand, the effect on CA was minor. The slight decrease in CA observed across the pressure range investigated could be attributed to an increase in the total number of H-bonds between fluid molecules and quartz surface.
Additives such as surfactants are commonly used to enhance the remediation of oil-contaminated ro... more Additives such as surfactants are commonly used to enhance the remediation of oil-contaminated rocks. Although the majority of crude oils are light nonaqueous phase liquids (LNAPLs), they often contain heavy molecules such as asphaltenes that are classified as dense nonaqueous phase liquids (DNAPLs). Surfactants are able to reduce the interfacial tension between water and LNAPLs and enhance their mobilization. Furthermore, the formation of microemulsions by surfactants can promote the solubilization of DNAPLs and restore the wettability of contaminated surfaces. Numerous studies have indicated that surfactants can promote the cleanup of oil-contaminated rocks; however, the impact of surfactant structure on solubilization and mobilization is still unclear. In this study, we investigated the remediation of heterogeneous aquifer rocks using four different nonionic surfactants: n-dodecyl β-D-maltoside, Triton X-100, Biosoft N1-7, and Saponin. The goal was to develop an improved understanding of the role of the surfactant molecular structure on nonaqueous phase liquids (NAPLs) removal through solubilization and mobilization. Each of these surfactants has a unique structural characteristic in its hydrophilic or hydrophobic segment. Dodecyl β-D-maltoside contains hydroxyl groups in its hydrophilic segment, which tend to form strong hydrogen bonds, while Triton X-100 has branched-chain alkyl groups in its hydrophobic segment that are more soluble in NAPL. Alkyl ethoxylated surfactants such as N1-7 display the simplest structure, while saponin with a heavy and complex structure cannot solubilize NAPLs as fast as other surfactants. Through measurements of phase behavior, dynamic interfacial properties, adsorption, spontaneous imbibition, thin sections analysis, and high resolution transmission electron microscopy, we showed that microemulsions formed by these surfactants are able to mobilize LNAPLs, especially in the presence of branched-chain alkyl groups in the hydrophobic segments (such as those in Triton X-100), which promoted higher reduction in the interfacial tension between NAPL and brine. Micellar solubilization, on the other hand, was favored by the hydroxyl groups in hydrophilic segments (such as those in n-dodecyl β-D-maltoside), which were able to form strong hydrogen bonds at interfaces and favor the desorption of DNAPL from mineral surfaces. Following a different trend from the other surfactants, saponin with a higher solubility in brine showed a tendency to self-aggregate and form micron-size clusters of microemulsions, which slowed down the NAPL remediation.
The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oi... more The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oilfields. The prediction of adsorption thickness using conventional techniques, such as quartz crystal microbalance (QCM), is usually costly and time-consuming. Alternatively, the adsorption can be related to asphaltene characteristics in the bulk phase that are easier to determine. This study investigates the relationship between the adsorption thickness of asphaltenes on hydrophilic surfaces, such as gold, and their electrical conductivity in toluene within a range of concentrations where adsorption is diffusion-controlled. The method is based on the measurement of direct-current (DC) conductivity of petroleum fluids in toluene using the impedance spectroscopy (IS) method. An inverse relationship is established between the thickness of adsorbed rigid monolayer films on gold and the conductivity of particles in the bulk fluid. However, the relation does not hold for small asphaltene particles (d < 3 nm) because they tend to form non-uniform multilayers with possible viscoelastic characteristics.
ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to bet... more ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to better understand the mechanisms of emulsion stabilization and electrically induced separations. A quartz crystal microbalance (QCM) with nanogram sensitivity is used to determine the electrodeposited mass in toluene-based systems. The use of low voltages for the first time allows a small amount of deposited material to be determined accurately. The method consists of applying a DC voltage between two gold-coated QCM crystals immersed in toluene solutions of asphaltenes, maltenes, or solid-free bitumen. Application of a 250 V/cm electric field strength produces an electrocollection of cationic and anionic species at the negatively and positively charged QCM crystals, respectively. A small fraction of the electrocollected material eventually electrodeposits and forms a transparent colorless film at the electrode surfaces. The specific mass (i.e., mass over charge) is found to be higher for the positive species than it is for the negative species. With this method, the characteristic time of relaxation of the bituminous solutions is estimated during the early stage of voltage application. This time could be used to establish a minimum frequency criterion for the critical field methods of water electrocoalescence in oil. Solids separated from bitumen are mainly negatively charged, and their specific mass is relatively high. This study shows that electrodeposition can efficiently separate solids and solid-stabilized water droplets from bitumen. Thus, an electrostatic treatment processes could be successful in removing solids and water from diluted bitumen systems.
The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oi... more The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oilfields. The prediction of adsorption thickness using conventional techniques, such as quartz crystal microbalance (QCM), is usually costly and time-consuming. Alternatively, the adsorption can be related to asphaltene characteristics in the bulk phase that are easier to determine. This study investigates the relationship between the adsorption thickness of asphaltenes on hydrophilic surfaces, such as gold, and their electrical conductivity in toluene within a range of concentrations where adsorption is diffusion-controlled. The method is based on the measurement of direct-current (DC) conductivity of petroleum fluids in toluene using the impedance spectroscopy (IS) method. An inverse relationship is established between the thickness of adsorbed rigid monolayer films on gold and the conductivity of particles in the bulk fluid. However, the relation does not hold for small asphaltene particles (d < 3 nm) because they tend to form non-uniform multilayers with possible viscoelastic characteristics.
ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to bet... more ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to better understand the mechanisms of emulsion stabilization and electrically induced separations. A quartz crystal microbalance (QCM) with nanogram sensitivity is used to determine the electrodeposited mass in toluene-based systems. The use of low voltages for the first time allows a small amount of deposited material to be determined accurately. The method consists of applying a DC voltage between two gold-coated QCM crystals immersed in toluene solutions of asphaltenes, maltenes, or solid-free bitumen. Application of a 250 V/cm electric field strength produces an electrocollection of cationic and anionic species at the negatively and positively charged QCM crystals, respectively. A small fraction of the electrocollected material eventually electrodeposits and forms a transparent colorless film at the electrode surfaces. The specific mass (i.e., mass over charge) is found to be higher for the positive species than it is for the negative species. With this method, the characteristic time of relaxation of the bituminous solutions is estimated during the early stage of voltage application. This time could be used to establish a minimum frequency criterion for the critical field methods of water electrocoalescence in oil. Solids separated from bitumen are mainly negatively charged, and their specific mass is relatively high. This study shows that electrodeposition can efficiently separate solids and solid-stabilized water droplets from bitumen. Thus, an electrostatic treatment processes could be successful in removing solids and water from diluted bitumen systems.
International Journal of Greenhouse Gas Control, 2014
The successful implementation of geologic CO 2 sequestration schemes in deep saline aquifers requ... more The successful implementation of geologic CO 2 sequestration schemes in deep saline aquifers requires storage sites with minimum risk of CO 2 leakage through the caprock and maximum storage capacity in the reservoir rock. Some of the essential parameters that affect the effectiveness of a storage scheme are the density of CO 2 , the interfacial tension between CO 2 -rich and aqueous phases, and the wettability of reservoir rock and caprock in contact with these fluids at reservoir conditions . In this study, densities, interfacial tensions, and dynamic contact angles of CO 2 /brine/quartz systems at high temperatures and pressures were simultaneously measured using the Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method. Measurements were performed at pressures (2000-4000 psig), temperatures (50-100 • C), and brine salinities (0.2-5 M) relevant to carbon sequestration in deep saline aquifers. These experimental conditions had not been investigated in the past. Additionally, the effect of SO 2 as a co-contaminant (0-6 wt%) was investigated on these parameters for the first time. Contact angle hysteresis was also examined and the possible implications of the results on different CO 2 trapping mechanisms were discussed.
A model of the dominant molecular and stable colloidal structures of asphaltenes has been propose... more A model of the dominant molecular and stable colloidal structures of asphaltenes has been proposed, the Yen− 10 Mullins model. The formation of clusters of asphaltene nanoaggregates in toluene was reported elsewhere to occur at a 11 concentration of a few grams per liter with a cluster aggregation number of approximately 8. 1 Here, we measure the DC-12 conductivity signal of toluene as a function of asphaltene concentration obtaining support for the critical clustering concentration 13 (CCC) of a roughly 1.7 g/L in toluene. In addition, the small change in the Stokes drag at the CCC indicates that the cluster 14 aggregation number is small, less than 10. The temperature variation of the CCC is measured to be small and within error, 15 suggesting that cluster formation is entropically driven. Centrifugation experiments were also performed on asphaltene−toluene 16 solutions at different concentrations. These experiments confirmed that a significant change in asphaltene aggregation occurs in 17 the concentration range of the CCC. The CCC values from centrifugation and DC-conductivity measurements are roughly the 18 same. The centrifugation experiments confirm a cluster size of ∼5 nm corroborating the small aggregation number found in the 19 DC-conductivity experiments. These results add to the growing body of literature validating the Yen−Mullins model. 20 ■ INTRODUCTION 21
The dispersion of asphaltenes by dodecylbenzenesulfonic acid (DBSA) has been the subject of sever... more The dispersion of asphaltenes by dodecylbenzenesulfonic acid (DBSA) has been the subject of several studies in the past. However, it is unclear how these interactions affect the structure of asphaltenes and why asphaltene aggregates are larger in the presence of ionic DBSA. The main goal of this study was to address these points using a combination of high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) simulations. Another objective was to compare ionic DBSA (i.e., dodecylbenzenesulfonate or DBS À ) to nonionic amphiphiles such as alkylphenols. A striking similarity between dodecylbenzenesulfonate and alkylphenols was that both favored the formation of filamentary rather than globular asphaltene flocculates. However the mechanism by which those filaments formed was very different. Two strong electrostatic interactions between DBSA and asphaltenes were found: (i) those between protonated asphaltenes (i.e., AH + ) and DBS À molecules, which were fifteen times stronger than asphaltene-alkylphenol interactions, and (ii) those between two asphaltene-dispersant pairs (i.e., AH + -DBS À ion pairs), which did not exist with alkylphenols. These interactions promoted the formation of large and compact asphaltene flocculates, as compared to small and loose ones formed without DBSA. Flocculates with DBSA could further bind to each other through ion-pair interactions. The binding occurred in series (generating long filaments) or in parallel (generating lateral ramifications). However the series configuration was energetically favored due to less steric effects generated by the side aliphatic chains of asphaltenes and DBSA.
IFT/CA measurements were performed on shale systems at reservoir conditions. A framework is estab... more IFT/CA measurements were performed on shale systems at reservoir conditions. A framework is established to study surfactant concentration/brine chemistry on shales. Increase in salinity and anionic surfactant concentration resulted in higher CA. Shale remained water-wet due to low adsorption of nonionic surfactant. Use of tap water versus reservoir brine resulted in lower IFT and work of adhesion.
Surfactant-enhanced aquifer remediation is often performed to overcome the capillary forces that ... more Surfactant-enhanced aquifer remediation is often performed to overcome the capillary forces that keep residual NAPL phases trapped within contaminated aquifers. The surfactant selection and displacement mechanism usually depend on the nature of NAPL constituents. For example, micellar solubilization is often used to cleanup DNAPLs from aquifers whereas mobilization is desirable in aquifers contaminated by LNAPLs. Although the majority of crude oils are LNAPLs, they often contain heavy organic macromolecules such as asphaltenes that are classified as DNAPLs. Asphaltenes contain surface-active components that tend to adsorb on rocks, altering their wettability. Previous studies revealed that surfactants that formed Winsor type III microemulsions could promote both mobilization and solubilization. However the extent by which these two mechanisms occur is still unclear, particularly in oil-contaminated aquifers. In this study we investigated the remediation of oil-contaminated aquifers using an environmentally friendly surfactant such as n-Dodecyl β-D-maltoside. Focus was given on asphaltenes to better understand the mechanisms of surfactant cleanup. Through phase behavior, spontaneous imbibition, dynamic interfacial tension and contact angle measurements, we showed that microemulsions formed by this surfactant are able to mobilize bulk NAPL (containing 9wt.% asphaltenes) in the porous rock and solubilize DNAPL (i.e., 4-6wt.% adsorbed asphaltenes) from the rock surface. Spontaneous imbibition tests, in particular, indicated that the ratio of mobilized to solubilized NAPL is about 6:1. Furthermore, aging the cores in NAPL beyond 3days allowed for more NAPL to be trapped in the large pores of the rock but did not alter the amount of asphaltenes adsorbed on the mineral surface.
The safe trapping of carbon dioxide (CO 2) in deep saline aquifers is one of the major concerns o... more The safe trapping of carbon dioxide (CO 2) in deep saline aquifers is one of the major concerns of CO 2 sequestration. The amount of capillary trapping is dominated by the capillary pressure of water and CO 2 inside the reservoir, which in turn is controlled by the interfacial tension (IFT) and the contact angle (CA) of CO 2 /water/rock systems. The measurement of IFT and CA could be very challenging at reservoir conditions, especially in the presence of toxic cocontaminants. Thus, the ability to accurately predict these interfacial properties at reservoir conditions is very advantageous. Although the majority of existing molecular dynamics (MD) studies of CO 2 /water/mineral systems were able to capture the trends in IFT and CA variations with pressure and temperature, their predictions often deviated from experimental data, possibly due to erroneous models and/or overlooked chemical reactions. The objective of this study was to improve the MD predictions of IFT and CA of CO 2 / water/quartz systems at various pressure and temperature conditions by (i) considering the chemical reactions between CO 2 and water and (ii) using a new molecular model for α-quartz surface. The results showed that the presence of carbonic acid at the CO 2 /water interface improved the predictions of IFT, especially at low temperature and high pressure where more CO 2 dissolution occurs. On the other hand, the effect on CA was minor. The slight decrease in CA observed across the pressure range investigated could be attributed to an increase in the total number of H-bonds between fluid molecules and quartz surface.
Additives such as surfactants are commonly used to enhance the remediation of oil-contaminated ro... more Additives such as surfactants are commonly used to enhance the remediation of oil-contaminated rocks. Although the majority of crude oils are light nonaqueous phase liquids (LNAPLs), they often contain heavy molecules such as asphaltenes that are classified as dense nonaqueous phase liquids (DNAPLs). Surfactants are able to reduce the interfacial tension between water and LNAPLs and enhance their mobilization. Furthermore, the formation of microemulsions by surfactants can promote the solubilization of DNAPLs and restore the wettability of contaminated surfaces. Numerous studies have indicated that surfactants can promote the cleanup of oil-contaminated rocks; however, the impact of surfactant structure on solubilization and mobilization is still unclear. In this study, we investigated the remediation of heterogeneous aquifer rocks using four different nonionic surfactants: n-dodecyl β-D-maltoside, Triton X-100, Biosoft N1-7, and Saponin. The goal was to develop an improved understanding of the role of the surfactant molecular structure on nonaqueous phase liquids (NAPLs) removal through solubilization and mobilization. Each of these surfactants has a unique structural characteristic in its hydrophilic or hydrophobic segment. Dodecyl β-D-maltoside contains hydroxyl groups in its hydrophilic segment, which tend to form strong hydrogen bonds, while Triton X-100 has branched-chain alkyl groups in its hydrophobic segment that are more soluble in NAPL. Alkyl ethoxylated surfactants such as N1-7 display the simplest structure, while saponin with a heavy and complex structure cannot solubilize NAPLs as fast as other surfactants. Through measurements of phase behavior, dynamic interfacial properties, adsorption, spontaneous imbibition, thin sections analysis, and high resolution transmission electron microscopy, we showed that microemulsions formed by these surfactants are able to mobilize LNAPLs, especially in the presence of branched-chain alkyl groups in the hydrophobic segments (such as those in Triton X-100), which promoted higher reduction in the interfacial tension between NAPL and brine. Micellar solubilization, on the other hand, was favored by the hydroxyl groups in hydrophilic segments (such as those in n-dodecyl β-D-maltoside), which were able to form strong hydrogen bonds at interfaces and favor the desorption of DNAPL from mineral surfaces. Following a different trend from the other surfactants, saponin with a higher solubility in brine showed a tendency to self-aggregate and form micron-size clusters of microemulsions, which slowed down the NAPL remediation.
The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oi... more The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oilfields. The prediction of adsorption thickness using conventional techniques, such as quartz crystal microbalance (QCM), is usually costly and time-consuming. Alternatively, the adsorption can be related to asphaltene characteristics in the bulk phase that are easier to determine. This study investigates the relationship between the adsorption thickness of asphaltenes on hydrophilic surfaces, such as gold, and their electrical conductivity in toluene within a range of concentrations where adsorption is diffusion-controlled. The method is based on the measurement of direct-current (DC) conductivity of petroleum fluids in toluene using the impedance spectroscopy (IS) method. An inverse relationship is established between the thickness of adsorbed rigid monolayer films on gold and the conductivity of particles in the bulk fluid. However, the relation does not hold for small asphaltene particles (d < 3 nm) because they tend to form non-uniform multilayers with possible viscoelastic characteristics.
ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to bet... more ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to better understand the mechanisms of emulsion stabilization and electrically induced separations. A quartz crystal microbalance (QCM) with nanogram sensitivity is used to determine the electrodeposited mass in toluene-based systems. The use of low voltages for the first time allows a small amount of deposited material to be determined accurately. The method consists of applying a DC voltage between two gold-coated QCM crystals immersed in toluene solutions of asphaltenes, maltenes, or solid-free bitumen. Application of a 250 V/cm electric field strength produces an electrocollection of cationic and anionic species at the negatively and positively charged QCM crystals, respectively. A small fraction of the electrocollected material eventually electrodeposits and forms a transparent colorless film at the electrode surfaces. The specific mass (i.e., mass over charge) is found to be higher for the positive species than it is for the negative species. With this method, the characteristic time of relaxation of the bituminous solutions is estimated during the early stage of voltage application. This time could be used to establish a minimum frequency criterion for the critical field methods of water electrocoalescence in oil. Solids separated from bitumen are mainly negatively charged, and their specific mass is relatively high. This study shows that electrodeposition can efficiently separate solids and solid-stabilized water droplets from bitumen. Thus, an electrostatic treatment processes could be successful in removing solids and water from diluted bitumen systems.
The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oi... more The adsorption of asphaltenes on solid surfaces can be the precursor of deposition problems in oilfields. The prediction of adsorption thickness using conventional techniques, such as quartz crystal microbalance (QCM), is usually costly and time-consuming. Alternatively, the adsorption can be related to asphaltene characteristics in the bulk phase that are easier to determine. This study investigates the relationship between the adsorption thickness of asphaltenes on hydrophilic surfaces, such as gold, and their electrical conductivity in toluene within a range of concentrations where adsorption is diffusion-controlled. The method is based on the measurement of direct-current (DC) conductivity of petroleum fluids in toluene using the impedance spectroscopy (IS) method. An inverse relationship is established between the thickness of adsorbed rigid monolayer films on gold and the conductivity of particles in the bulk fluid. However, the relation does not hold for small asphaltene particles (d < 3 nm) because they tend to form non-uniform multilayers with possible viscoelastic characteristics.
ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to bet... more ABSTRACT This work aims to identify the nature of the charge carriers in Athabasca bitumen to better understand the mechanisms of emulsion stabilization and electrically induced separations. A quartz crystal microbalance (QCM) with nanogram sensitivity is used to determine the electrodeposited mass in toluene-based systems. The use of low voltages for the first time allows a small amount of deposited material to be determined accurately. The method consists of applying a DC voltage between two gold-coated QCM crystals immersed in toluene solutions of asphaltenes, maltenes, or solid-free bitumen. Application of a 250 V/cm electric field strength produces an electrocollection of cationic and anionic species at the negatively and positively charged QCM crystals, respectively. A small fraction of the electrocollected material eventually electrodeposits and forms a transparent colorless film at the electrode surfaces. The specific mass (i.e., mass over charge) is found to be higher for the positive species than it is for the negative species. With this method, the characteristic time of relaxation of the bituminous solutions is estimated during the early stage of voltage application. This time could be used to establish a minimum frequency criterion for the critical field methods of water electrocoalescence in oil. Solids separated from bitumen are mainly negatively charged, and their specific mass is relatively high. This study shows that electrodeposition can efficiently separate solids and solid-stabilized water droplets from bitumen. Thus, an electrostatic treatment processes could be successful in removing solids and water from diluted bitumen systems.
International Journal of Greenhouse Gas Control, 2014
The successful implementation of geologic CO 2 sequestration schemes in deep saline aquifers requ... more The successful implementation of geologic CO 2 sequestration schemes in deep saline aquifers requires storage sites with minimum risk of CO 2 leakage through the caprock and maximum storage capacity in the reservoir rock. Some of the essential parameters that affect the effectiveness of a storage scheme are the density of CO 2 , the interfacial tension between CO 2 -rich and aqueous phases, and the wettability of reservoir rock and caprock in contact with these fluids at reservoir conditions . In this study, densities, interfacial tensions, and dynamic contact angles of CO 2 /brine/quartz systems at high temperatures and pressures were simultaneously measured using the Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method. Measurements were performed at pressures (2000-4000 psig), temperatures (50-100 • C), and brine salinities (0.2-5 M) relevant to carbon sequestration in deep saline aquifers. These experimental conditions had not been investigated in the past. Additionally, the effect of SO 2 as a co-contaminant (0-6 wt%) was investigated on these parameters for the first time. Contact angle hysteresis was also examined and the possible implications of the results on different CO 2 trapping mechanisms were discussed.
A model of the dominant molecular and stable colloidal structures of asphaltenes has been propose... more A model of the dominant molecular and stable colloidal structures of asphaltenes has been proposed, the Yen− 10 Mullins model. The formation of clusters of asphaltene nanoaggregates in toluene was reported elsewhere to occur at a 11 concentration of a few grams per liter with a cluster aggregation number of approximately 8. 1 Here, we measure the DC-12 conductivity signal of toluene as a function of asphaltene concentration obtaining support for the critical clustering concentration 13 (CCC) of a roughly 1.7 g/L in toluene. In addition, the small change in the Stokes drag at the CCC indicates that the cluster 14 aggregation number is small, less than 10. The temperature variation of the CCC is measured to be small and within error, 15 suggesting that cluster formation is entropically driven. Centrifugation experiments were also performed on asphaltene−toluene 16 solutions at different concentrations. These experiments confirmed that a significant change in asphaltene aggregation occurs in 17 the concentration range of the CCC. The CCC values from centrifugation and DC-conductivity measurements are roughly the 18 same. The centrifugation experiments confirm a cluster size of ∼5 nm corroborating the small aggregation number found in the 19 DC-conductivity experiments. These results add to the growing body of literature validating the Yen−Mullins model. 20 ■ INTRODUCTION 21
The dispersion of asphaltenes by dodecylbenzenesulfonic acid (DBSA) has been the subject of sever... more The dispersion of asphaltenes by dodecylbenzenesulfonic acid (DBSA) has been the subject of several studies in the past. However, it is unclear how these interactions affect the structure of asphaltenes and why asphaltene aggregates are larger in the presence of ionic DBSA. The main goal of this study was to address these points using a combination of high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) simulations. Another objective was to compare ionic DBSA (i.e., dodecylbenzenesulfonate or DBS À ) to nonionic amphiphiles such as alkylphenols. A striking similarity between dodecylbenzenesulfonate and alkylphenols was that both favored the formation of filamentary rather than globular asphaltene flocculates. However the mechanism by which those filaments formed was very different. Two strong electrostatic interactions between DBSA and asphaltenes were found: (i) those between protonated asphaltenes (i.e., AH + ) and DBS À molecules, which were fifteen times stronger than asphaltene-alkylphenol interactions, and (ii) those between two asphaltene-dispersant pairs (i.e., AH + -DBS À ion pairs), which did not exist with alkylphenols. These interactions promoted the formation of large and compact asphaltene flocculates, as compared to small and loose ones formed without DBSA. Flocculates with DBSA could further bind to each other through ion-pair interactions. The binding occurred in series (generating long filaments) or in parallel (generating lateral ramifications). However the series configuration was energetically favored due to less steric effects generated by the side aliphatic chains of asphaltenes and DBSA.
IFT/CA measurements were performed on shale systems at reservoir conditions. A framework is estab... more IFT/CA measurements were performed on shale systems at reservoir conditions. A framework is established to study surfactant concentration/brine chemistry on shales. Increase in salinity and anionic surfactant concentration resulted in higher CA. Shale remained water-wet due to low adsorption of nonionic surfactant. Use of tap water versus reservoir brine resulted in lower IFT and work of adhesion.
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Papers by Lamia Goual