Asphaltene precipitation and deposition can occur at different stages during petroleum production... more Asphaltene precipitation and deposition can occur at different stages during petroleum production, causing reservoir formation damage and plugging of pipeline and production equipment. Predicting asphaltene flow assurance issues requires the ability to model the phase behavior of asphaltenes as a function of the temperature, pressure, and composition. In this paper, we briefly review some recent approaches to model asphaltene phase behavior. We also present a method to characterize crude oil, including asphaltenes using the perturbed chain form of the statistical associating fluid theory (PC-SAFT). The theory accurately predicts the crude oil bubble point and density as well as asphaltene precipitation conditions. The theory is used to examine the effects of gas injection, oil-based mud contamination, and asphaltene polydispersity on the phase behavior of asphaltenes. The analysis produces some interesting insights into field and laboratory observations of asphaltene phase behavior.
Gas injection is one of the main types of Enhanced Oil Recovery (EOR) techniques that can recover... more Gas injection is one of the main types of Enhanced Oil Recovery (EOR) techniques that can recover significant amounts of residual oil. One of the challenges of applying EOR gas injection in reservoirs is the potential of asphaltene precipitation and subsequent deposition. The probability of asphaltene precipitation increases dramatically when light gases are considered for miscible gas injection [1]. Proper predictions of the asphaltene onsets at these conditions represent a challenge for reservoir modeling and flow assurance applications. Anadarko Petroleum Corporation, Ecopetrol S.A. and Schlumberger have jointly investigated the effects of gas addition to the phase behavior of oil, especially its effect on asphaltene precipitation. In this work, the prediction of the asphaltene phase behavior in a live fluid and dead oil from deepwater GOM is investigated in a range of pressures and temperatures in the presence of carbon dioxide, nitrogen and methane using cubic-plus-association ...
Deepwater exploration and development has become a key target for the majority of oil and gas E&P... more Deepwater exploration and development has become a key target for the majority of oil and gas E&P Companies because of the large potential reserves and increase in oil prices. Development activities in deepwater face significant challenges. Flow assurance becomes a significantly greater component in production economics due to the increase of intervention costs. Of particular concern are the effects of produced fluid hydrocarbon solids (i.e. asphaltene, wax, and hydrates) precipitation and their potential to disrupt production due to deposition in the near-wellbore regions and production tubulars. Besides hydrocarbon solids, other production hindrance elements include wellbore fluid loading, fluid slugging, inorganics, corrosion, erosion and emulsions. All these elements adversely affect production assurance in deepwater systems and are key risk factors in assessing deepwater developments. The production assurance risk factors can create game-changing impact on field development pla...
Asphaltenes are the heaviest and most polarizable components of crude oil. The phase behavior of ... more Asphaltenes are the heaviest and most polarizable components of crude oil. The phase behavior of these polydisperse components is important in both the upstream and downstream processing of crude oil because of their potential to precipitate, deposit and plug pipelines and production equipment. Predicting flow assurance issues caused by asphaltenes requires the ability to model the phase behavior of asphaltenes as a function of temperature, pressure, and composition. In this work we present a detailed procedure to characterize crude oil and plot asphaltene phase envelope, using the Perturbed Chain form of the Statistical Associating Fluid Theory (PC-SAFT). This work also demonstrates that the proposed procedure can model the asphaltene thermodynamic phase behavior better than using a cubic equation of state typically used in the industry, even with compositional data as low as C 9 +.
ABSTRACT The asphaltene content effect on crude oil properties was investigated for a series of d... more ABSTRACT The asphaltene content effect on crude oil properties was investigated for a series of deepwater Gulf of Mexico (GOM) fluids with asphaltene contents varying from 4 to 15 wt %. The objective of the study was to conduct flow assurance screening tests on GOM samples collected from different sands and determine properties of the dead oil and the asphaltene stability. Densities, refractive indices, and viscosities were measured at different temperatures in dead oils with three different asphaltene contents. The properties showed defined tendencies with the asphaltene content and with the temperature. The application of the one-third rule in the calculation of properties, such as solubility parameter and viscosity of dead oil systems, was evaluated. This approach also provides an alternative to calculate the refractive index based on densities obtained from an equation of state. The analysis also shows the important role that the asphaltene content plays in determining the viscosity of crude oil and evaluates the possibility of predicting viscosity from refractive index, as proposed by Vargas et al. Another important aspect to evaluate is the prediction of the asphaltene stability in the crude oil by measuring basic dead oil properties, such as density and refractive index. The asphaltene instability trend (ASIST) method was used to predict the asphaltene precipitation onset at reservoir conditions. In this analysis, the asphaltene stability was studied on the heaviest and lightest samples (high and low asphaltene content) by determining the minimum quantity of precipitant required to initiate asphaltene flocculation, followed by measurement of the refractive index of the mixture at the onset conditions. The asphaltene precipitation kinetic effect was also considered in this study.
Asphaltene precipitation and deposition adversely affect production assurance and are key risk fa... more Asphaltene precipitation and deposition adversely affect production assurance and are key risk factors in assessing difficult environments such as deepwater. Deposition in the near well bore regions and production tubulars implies high intervention and remediation costs. Prediction of asphaltene precipitation onset represents a challenge for the flow assurance area. The applicability of the PC-SAFT equation of state model to predict asphaltene onset of the precipitation in live oils is demonstrated by studying representative examples from field experiences with asphaltene problems during production. These examples not only validate the proposed model but also confirm the theory that asphaltene phase behavior can be explained based only on molecular size and van der Waals interactions. The PC-SAFT equation of state estimates also properties such as densities and bubble points of live oil systems using a minimum number of real components and "realistic" pseudocomponents. The amount and composition of the asphaltene precipitated phase is also determined as part of the equilibrium calculations. This paper presents experimental observations and simulation results at reservoir conditions using the PC-SAFT equation of state on the effect of compositional changes in live oils caused by two common processes in the oil industry: oil-based-mud (OBM) contamination and reinjection of associated gas. In the first case, the downhole oil samples can be contaminated with OBM, causing laboratory measurements of the bubble point and asphaltene precipitation to be different from the reservoir fluid. In the second case, the reinjection of gas into the field increases the gas-oil-ratio (GOR) of the oil. The addition of gas into the oil can cause asphaltene precipitation and deposition due to the increase of light components that reduces asphaltene solubility. Asphaltenes in this example are treated as both monodisperse and polydisperse pseudocomponents. From the obtained results, it can be concluded that the live oil modeled using the PC-SAFT equation of state properly predicts the asphaltene phase behavior under these compositional changes. The PC-SAFT equation of state model is a commercially available, proven tool.
The insolubility of asphaltenes in light paraffin liquids and other incompatible fluids, such as ... more The insolubility of asphaltenes in light paraffin liquids and other incompatible fluids, such as carbon dioxide (CO 2 ), is a source of problems during crude oil production operations. Asphaltene precipitation can cause formation damage and wellbore plugging, requiring expensive treatment and cleanup procedures. In the presence of light gases, such methane, ethane, propane, and nitrogen (N 2 ), asphaltenes are usually more stable as pressure and temperature increase; however, experimental measurements indicate that, in the presence of CO 2 , asphaltenes become more stable as the temperature decreases. In this work, the asphaltene phase behavior in a live reservoir fluid and a dead oil from South America is investigated in a range of pressures and temperatures in the presence of CO 2 using the perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state (EoS). This thermodynamic model has been applied to asphaltene precipitation with different crude oil systems, such as those that involve methane, ethane, or N 2 . Simulation results using the PC-SAFT EoS model are in good agreement with experimental measurements. A thermodynamic analysis using a model live oil confirms and explains a crossover behavior observed in the simulation of the precipitation onset with CO 2 . Simulations show that CO 2 can act as an inhibitor or a promoter of asphaltene precipitation depending upon the range of temperature, pressure, and composition studied. At fixed pressure and live oil composition, CO 2 addition increases the asphaltene stability below the crossover temperature, whereas above this point, the asphaltene becomes less stable when the CO 2 concentration is increased.
Proper prediction of the potential for asphaltene precipitation in deepwater reservoirs represent... more Proper prediction of the potential for asphaltene precipitation in deepwater reservoirs represents a challenge for the flow assurance area due to both high intervention costs in case of asphaltene problems and extreme conditions of pressure, temperature, and composition. The probability of asphaltene precipitation increases when light-oil gases are considered for miscible gas injection processes. In this work, the applicability of simple and recombined live oil models using the PC-SAFT equation of state to predict the onset of asphaltene precipitation is demonstrated by studying pressure depletion and gas injection (carbon dioxide (CO 2 ), nitrogen (N 2 ), methane, and ethane) in oil reservoirs. The recombined model input includes the SARA characterization, the oil compositional analysis, and the gas-oil ratio. The pure component PC-SAFT parameters are fitted to the saturated liquid density and vapor pressure data, and the oil/gas pseudocomponent parameters are estimated from molecular-weight-based correlations. The EOS asphaltene parameters are fitted to precipitation data from oil titration with n-alkanes at ambient conditions. When asphaltene experimental data are not available, the asphaltene parameters are tuned to data at reservoir conditions, and then the model is run in a predictive mode. The PC-SAFT model was found to be in qualitative agreement with experimental data for the precipitant/crude oil systems in this study. In the prediction of the asphaltene onset using the model live oil, the results indicate that the ethane and CO 2 mass fraction concentrations required to produce asphaltene precipitation is greater than for methane at the same pressure. Simulation results using the recombined model show that N 2 addition produces a high asphaltene precipitation effect even at low concentrations. The simulated phase envelope for liquid-liquid asphaltene phase separation shows asphaltene stability bounded by an upper critical solution temperature and a lower critical solution temperature. The approach demonstrates that only molecular size and van der Waals interactions can explain laboratory and field observations of asphaltene phase behavior.
Asphaltene precipitation and deposition can occur at different stages during petroleum production... more Asphaltene precipitation and deposition can occur at different stages during petroleum production, causing reservoir formation damage and plugging of pipeline and production equipment. Predicting asphaltene flow assurance issues requires the ability to model the phase behavior of asphaltenes as a function of the temperature, pressure, and composition. In this paper, we briefly review some recent approaches to model asphaltene phase behavior. We also present a method to characterize crude oil, including asphaltenes using the perturbed chain form of the statistical associating fluid theory (PC-SAFT). The theory accurately predicts the crude oil bubble point and density as well as asphaltene precipitation conditions. The theory is used to examine the effects of gas injection, oil-based mud contamination, and asphaltene polydispersity on the phase behavior of asphaltenes. The analysis produces some interesting insights into field and laboratory observations of asphaltene phase behavior.
Asphaltene precipitation and deposition can occur at different stages during petroleum production... more Asphaltene precipitation and deposition can occur at different stages during petroleum production, causing reservoir formation damage and plugging of pipeline and production equipment. Predicting asphaltene flow assurance issues requires the ability to model the phase behavior of asphaltenes as a function of the temperature, pressure, and composition. In this paper, we briefly review some recent approaches to model asphaltene phase behavior. We also present a method to characterize crude oil, including asphaltenes using the perturbed chain form of the statistical associating fluid theory (PC-SAFT). The theory accurately predicts the crude oil bubble point and density as well as asphaltene precipitation conditions. The theory is used to examine the effects of gas injection, oil-based mud contamination, and asphaltene polydispersity on the phase behavior of asphaltenes. The analysis produces some interesting insights into field and laboratory observations of asphaltene phase behavior.
Gas injection is one of the main types of Enhanced Oil Recovery (EOR) techniques that can recover... more Gas injection is one of the main types of Enhanced Oil Recovery (EOR) techniques that can recover significant amounts of residual oil. One of the challenges of applying EOR gas injection in reservoirs is the potential of asphaltene precipitation and subsequent deposition. The probability of asphaltene precipitation increases dramatically when light gases are considered for miscible gas injection [1]. Proper predictions of the asphaltene onsets at these conditions represent a challenge for reservoir modeling and flow assurance applications. Anadarko Petroleum Corporation, Ecopetrol S.A. and Schlumberger have jointly investigated the effects of gas addition to the phase behavior of oil, especially its effect on asphaltene precipitation. In this work, the prediction of the asphaltene phase behavior in a live fluid and dead oil from deepwater GOM is investigated in a range of pressures and temperatures in the presence of carbon dioxide, nitrogen and methane using cubic-plus-association ...
Deepwater exploration and development has become a key target for the majority of oil and gas E&P... more Deepwater exploration and development has become a key target for the majority of oil and gas E&P Companies because of the large potential reserves and increase in oil prices. Development activities in deepwater face significant challenges. Flow assurance becomes a significantly greater component in production economics due to the increase of intervention costs. Of particular concern are the effects of produced fluid hydrocarbon solids (i.e. asphaltene, wax, and hydrates) precipitation and their potential to disrupt production due to deposition in the near-wellbore regions and production tubulars. Besides hydrocarbon solids, other production hindrance elements include wellbore fluid loading, fluid slugging, inorganics, corrosion, erosion and emulsions. All these elements adversely affect production assurance in deepwater systems and are key risk factors in assessing deepwater developments. The production assurance risk factors can create game-changing impact on field development pla...
Asphaltenes are the heaviest and most polarizable components of crude oil. The phase behavior of ... more Asphaltenes are the heaviest and most polarizable components of crude oil. The phase behavior of these polydisperse components is important in both the upstream and downstream processing of crude oil because of their potential to precipitate, deposit and plug pipelines and production equipment. Predicting flow assurance issues caused by asphaltenes requires the ability to model the phase behavior of asphaltenes as a function of temperature, pressure, and composition. In this work we present a detailed procedure to characterize crude oil and plot asphaltene phase envelope, using the Perturbed Chain form of the Statistical Associating Fluid Theory (PC-SAFT). This work also demonstrates that the proposed procedure can model the asphaltene thermodynamic phase behavior better than using a cubic equation of state typically used in the industry, even with compositional data as low as C 9 +.
ABSTRACT The asphaltene content effect on crude oil properties was investigated for a series of d... more ABSTRACT The asphaltene content effect on crude oil properties was investigated for a series of deepwater Gulf of Mexico (GOM) fluids with asphaltene contents varying from 4 to 15 wt %. The objective of the study was to conduct flow assurance screening tests on GOM samples collected from different sands and determine properties of the dead oil and the asphaltene stability. Densities, refractive indices, and viscosities were measured at different temperatures in dead oils with three different asphaltene contents. The properties showed defined tendencies with the asphaltene content and with the temperature. The application of the one-third rule in the calculation of properties, such as solubility parameter and viscosity of dead oil systems, was evaluated. This approach also provides an alternative to calculate the refractive index based on densities obtained from an equation of state. The analysis also shows the important role that the asphaltene content plays in determining the viscosity of crude oil and evaluates the possibility of predicting viscosity from refractive index, as proposed by Vargas et al. Another important aspect to evaluate is the prediction of the asphaltene stability in the crude oil by measuring basic dead oil properties, such as density and refractive index. The asphaltene instability trend (ASIST) method was used to predict the asphaltene precipitation onset at reservoir conditions. In this analysis, the asphaltene stability was studied on the heaviest and lightest samples (high and low asphaltene content) by determining the minimum quantity of precipitant required to initiate asphaltene flocculation, followed by measurement of the refractive index of the mixture at the onset conditions. The asphaltene precipitation kinetic effect was also considered in this study.
Asphaltene precipitation and deposition adversely affect production assurance and are key risk fa... more Asphaltene precipitation and deposition adversely affect production assurance and are key risk factors in assessing difficult environments such as deepwater. Deposition in the near well bore regions and production tubulars implies high intervention and remediation costs. Prediction of asphaltene precipitation onset represents a challenge for the flow assurance area. The applicability of the PC-SAFT equation of state model to predict asphaltene onset of the precipitation in live oils is demonstrated by studying representative examples from field experiences with asphaltene problems during production. These examples not only validate the proposed model but also confirm the theory that asphaltene phase behavior can be explained based only on molecular size and van der Waals interactions. The PC-SAFT equation of state estimates also properties such as densities and bubble points of live oil systems using a minimum number of real components and "realistic" pseudocomponents. The amount and composition of the asphaltene precipitated phase is also determined as part of the equilibrium calculations. This paper presents experimental observations and simulation results at reservoir conditions using the PC-SAFT equation of state on the effect of compositional changes in live oils caused by two common processes in the oil industry: oil-based-mud (OBM) contamination and reinjection of associated gas. In the first case, the downhole oil samples can be contaminated with OBM, causing laboratory measurements of the bubble point and asphaltene precipitation to be different from the reservoir fluid. In the second case, the reinjection of gas into the field increases the gas-oil-ratio (GOR) of the oil. The addition of gas into the oil can cause asphaltene precipitation and deposition due to the increase of light components that reduces asphaltene solubility. Asphaltenes in this example are treated as both monodisperse and polydisperse pseudocomponents. From the obtained results, it can be concluded that the live oil modeled using the PC-SAFT equation of state properly predicts the asphaltene phase behavior under these compositional changes. The PC-SAFT equation of state model is a commercially available, proven tool.
The insolubility of asphaltenes in light paraffin liquids and other incompatible fluids, such as ... more The insolubility of asphaltenes in light paraffin liquids and other incompatible fluids, such as carbon dioxide (CO 2 ), is a source of problems during crude oil production operations. Asphaltene precipitation can cause formation damage and wellbore plugging, requiring expensive treatment and cleanup procedures. In the presence of light gases, such methane, ethane, propane, and nitrogen (N 2 ), asphaltenes are usually more stable as pressure and temperature increase; however, experimental measurements indicate that, in the presence of CO 2 , asphaltenes become more stable as the temperature decreases. In this work, the asphaltene phase behavior in a live reservoir fluid and a dead oil from South America is investigated in a range of pressures and temperatures in the presence of CO 2 using the perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state (EoS). This thermodynamic model has been applied to asphaltene precipitation with different crude oil systems, such as those that involve methane, ethane, or N 2 . Simulation results using the PC-SAFT EoS model are in good agreement with experimental measurements. A thermodynamic analysis using a model live oil confirms and explains a crossover behavior observed in the simulation of the precipitation onset with CO 2 . Simulations show that CO 2 can act as an inhibitor or a promoter of asphaltene precipitation depending upon the range of temperature, pressure, and composition studied. At fixed pressure and live oil composition, CO 2 addition increases the asphaltene stability below the crossover temperature, whereas above this point, the asphaltene becomes less stable when the CO 2 concentration is increased.
Proper prediction of the potential for asphaltene precipitation in deepwater reservoirs represent... more Proper prediction of the potential for asphaltene precipitation in deepwater reservoirs represents a challenge for the flow assurance area due to both high intervention costs in case of asphaltene problems and extreme conditions of pressure, temperature, and composition. The probability of asphaltene precipitation increases when light-oil gases are considered for miscible gas injection processes. In this work, the applicability of simple and recombined live oil models using the PC-SAFT equation of state to predict the onset of asphaltene precipitation is demonstrated by studying pressure depletion and gas injection (carbon dioxide (CO 2 ), nitrogen (N 2 ), methane, and ethane) in oil reservoirs. The recombined model input includes the SARA characterization, the oil compositional analysis, and the gas-oil ratio. The pure component PC-SAFT parameters are fitted to the saturated liquid density and vapor pressure data, and the oil/gas pseudocomponent parameters are estimated from molecular-weight-based correlations. The EOS asphaltene parameters are fitted to precipitation data from oil titration with n-alkanes at ambient conditions. When asphaltene experimental data are not available, the asphaltene parameters are tuned to data at reservoir conditions, and then the model is run in a predictive mode. The PC-SAFT model was found to be in qualitative agreement with experimental data for the precipitant/crude oil systems in this study. In the prediction of the asphaltene onset using the model live oil, the results indicate that the ethane and CO 2 mass fraction concentrations required to produce asphaltene precipitation is greater than for methane at the same pressure. Simulation results using the recombined model show that N 2 addition produces a high asphaltene precipitation effect even at low concentrations. The simulated phase envelope for liquid-liquid asphaltene phase separation shows asphaltene stability bounded by an upper critical solution temperature and a lower critical solution temperature. The approach demonstrates that only molecular size and van der Waals interactions can explain laboratory and field observations of asphaltene phase behavior.
Asphaltene precipitation and deposition can occur at different stages during petroleum production... more Asphaltene precipitation and deposition can occur at different stages during petroleum production, causing reservoir formation damage and plugging of pipeline and production equipment. Predicting asphaltene flow assurance issues requires the ability to model the phase behavior of asphaltenes as a function of the temperature, pressure, and composition. In this paper, we briefly review some recent approaches to model asphaltene phase behavior. We also present a method to characterize crude oil, including asphaltenes using the perturbed chain form of the statistical associating fluid theory (PC-SAFT). The theory accurately predicts the crude oil bubble point and density as well as asphaltene precipitation conditions. The theory is used to examine the effects of gas injection, oil-based mud contamination, and asphaltene polydispersity on the phase behavior of asphaltenes. The analysis produces some interesting insights into field and laboratory observations of asphaltene phase behavior.
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Papers by Doris Gonzalez