Solvent-aided Thermal Recovery Research Articles

Vapor-liquid-liquid equilibrium (VLLE), density, and viscosity of the ternary mixtures of normal hexane, water and bitumen at T=185–210°C and at P= 2.5 MPa

This paper presents a study on the vapor-liquid-liquid equilibrium (VLLE) of a ternary system consisting of normal-hexane (n-C6) as a solvent, water (H2O), and Mackay River bitumen. The study was conducted at temperatures ranging from 185 to 210 °C and a pressure of 2.5 MPa. The solvent/steam and solvent/bitumen ratios were varied to understand the effect of solvent (n-C6) on the phase behavior and the thermophysical properties of the associated phases. The co-injected solvent with steam is often reported as the concentration of solvent in the solvent/steam mixture. Two concentrations of n-C6 in n-C6/water mixture, including mole fractions of 0.01 and 0.05 (i.e., 6.85 and 27.70 vol.%), were considered to examine the effect of the co-injected solvent with steam. Also, two different mole fractions of n-C6 in the mixture of bitumen/n-C6 at 0.7 and 0.4 (37.45 and 14.61 vol.%), respectively, were considered to examine the effect of solvent solubility in bitumen. In addition to the VLLE study, the viscosity and density of the two distinct liquid phases, hydrocarbon-rich oleic and water-rich aqueous phases, were measured and reported. The results from the experiment infer that the concentration of n-C6 co-injected with steam does not significantly affect the equilibrium phase concentrations and thermophysical properties. However, the mixture showed liquid-liquid equilibria (LLE) instead of the vapor-liquid-liquid equilibria (VLLE) when the concentration of n-C6 in bitumen/solvent mixture was less than the equilibrium solubility of n-C6 in the hydrocarbon-rich phase at that operating condition. Furthermore, the results suggest that the presence of bitumen in equilibrium with n-C6 and H2O has no significant effect on the concentration of n-C6 in the vapor phase when compared with the n-C6/H2O binary mixture. Thermodynamic modelling of the VLLE data was performed using the cubic plus association equation of state (CPA EoS). The matching parameters were obtained by tuning the two-phase data, and those parameters were used in predicting the VLLE data. The model was also used to construct the phase regions of the solvent/bitumen/water system on the ternary diagram at different temperatures and pressures. Different phase regions were determined by phase stability analysis. The findings provide insight into steam/solvent condensation behavior with applications to the solvent-aided thermal recovery of bitumen from oil sands.

Solvent Content Measurements of the Produced Stable Water-in-Oil Emulsions During Solvent-Aided Thermal Recovery Processes

Solvent Content Measurements of the Produced Stable Water-in-Oil Emulsions During Solvent-Aided Thermal Recovery Processes

Measurements and Modeling of the Dissolution and Exsolution Kinetics of the Ethane/n-Heptane System

Solvent-aided thermal recovery processes have been suggested and implemented to reduce the environmental impact of steam-based heavy oil and bitumen production. The injected solvents often undergo dissolution (exsolution) into (from) the oil phase throughout the heavy oil and bitumen recovery processes. New experimental data at elevated pressures and temperatures are essential to better understand the dissolution and dissolution kinetics of various solvents. To eliminate this gap, a new experimental setup was developed to study the kinetics of exsolution and dissolution of gases. The developed setup was used to study the exsolution of ethane from ethane-saturated heptane and the dissolution of ethane in heptane in a temperature range of 60 to 120 °C. An analytical model was adapted to model the experiments and estimate the diffusion coefficients of exsolution and dissolution of the ethane/heptane system. The results indicate that the exsolution of ethane from heptane is much faster compared to its dissolution. The molecular diffusion coefficients for exsolution and dissolution were found to be in the range of (2.02–5.44) × 10–6 and (1.76–11.80) × 10–8 m2/s, respectively. The measured experimental data were modeled using the Arrhenius-type kinetics. The results revealed lower activation energy for the exsolution of ethane from ethane-saturated heptane compared to its dissolution. The reported dissolution and exsolution data sets find applications in the design, simulation, and optimization of solvent-aided thermal recovery of bitumen/heavy oil and various chemical processes.

A new chromatographic approach for bitumen characterization and solvent concentration measurement

Solvents are co-injected with steam into oil sands for dilution and mobilization of bitumen. Solvent recovery and solvent content of the produced bitumen are important economic parameters for the evaluation of the performance of solvent-aided thermal recovery processes. Measurement of solvent in the produced streams is challenging due to the component overlap between solvent and light components of bitumen. Additionally, the presence of water in the produced streams adds more complexity. This is due to the fact that the conventional solvent concentration measurement approaches rely on dewatering procedures that lead to significant solvent loss, making them incapable of accurate measurements. Currently, there is no established analytical method for the measurement of solvent fraction in bitumen-solvent blends. In this work, we have developed an analytical technique based on a combination of Gel Permeation Chromatography (GPC) and Gas Chromatography (GC) to fully characterize complex mixtures of bitumen and solvent and measure the solvent content of the production streams. The developed technique is validated using a known standard reference oil. The developed method was also applied for measuring solvent in the mixture of bitumen/solvent and bitumen/solvent/water mixtures. An average deviation of ± 0.16 was obtained for the solvent content of samples with different water content. It was shown that the proposed method is capable of measuring the solvent content of the produced bitumen in the absence and presence of water, eliminating the error in measurements due to solvent loss associated with dewatering procedures.

Subsurface Containment of Injected Chemicals during In-Situ Bitumen Recovery from Oil Sands

Reservoir containment of the injected fluids is essential in the solvent-aided thermal recovery of bitumen from oil sands from an environmental perspective. Containment is particularly important when new chemicals/solvents, known as Contaminants of Potential Concern (CoPCs), are coinjected with steam to improve the recovery process. In this work, numerical simulations are conducted to study the fate of the injected CoPCs such as propane, butane, hexane, field condensates, ammonia, dimethyl ether, and ethyl acetate. The results reveal that among the CoPCs studied, hexane, field condensates, and ethyl acetate are contained in the oil sands formations, whereas other CoPCs could potentially migrate upward. While upward migration of water-soluble CoPCs such as dimethyl ether and ammonia is limited to the top vicinity of the oil sands formation, propane could migrate upward significantly and reach shallow groundwater resources. Our findings also reveal that injection of solvents/chemicals, such as hexane, field condensates, and ethyl acetate, and to a great extent butane, eliminates migration of the in situ generated gases such as methane. In contrast, other solvents/chemicals such as propane, dimethyl ether, and ammonia allow significant upward migration of methane. These findings improve our understanding of the long-term fate of the injected CoPCs. In addition, the results find applications in the design of cleaner recovery techniques, risk assessment, and the development of regulatory frameworks for improved control on CoPCs.

Estimation of Viscosity of the N-Alkane (C1-C 4) in Bitumen System Using Adaptive Neuro-Fuzzy Interference System (ANFIS)

One of the important mechanisms in solvent-aided thermal recovery processes is viscosity reduction. Light n-alkane hydrocarbons are among the potential solvents for solvent-aided thermal recovery processes. In this study, the viscosity of C1- C4 n-alkanes in bitumen was investigated. Adaptive neuro-fuzzy interference system (ANFIS) was used for this aim. The result obtained by the ANFIS model analyzed with the statistical parameters (i.e., MSE, MEAE, MAAE, and R2) and graphical methods. Results show that the ANFIS has high capability to the prediction of solvent/bitumen mixture viscosity.

Solubility and Liquid Density of Ammonia/Athabasca Bitumen Mixtures at Temperatures up to 463 K: Measurements and Modeling

We report the experimental data of ammonia solubility in Athabasca bitumen measured at different temperatures and pressures ranging from 348 to 463 K and 1 to 4 MPa, respectively. The liquid-phase density of ammonia-saturated bitumen was measured for the samples that were taken during solubility measurements. The experimental data for ammonia solubility in bitumen were modeled using the Peng–Robinson equation of state. The volume-shift parameters of ammonia were tuned to represent the experimental density data of ammonia-saturated bitumen with an average absolute relative deviation percent (AARD%) of 0.218%. Also, tuning the binary interaction coefficient between ammonia and bitumen allowed the prediction of solubility data with an AARD of 8.537%. The data and the tuned model find applications in the reservoir modeling of solvent-aided thermal recovery of bitumen and heavy oil.

Development of Generalized Correlations for Thermophysical Properties of Light Hydrocarbon Solvents (C1–C5)/Bitumen Systems Using Genetic Programming

Accurate modeling of thermophysical properties of solvent/bitumen mixtures is critical for proper design and implementation of thermal- and solvent-based bitumen recovery processes. In this study, three generalized correlations were developed for prediction of solubility, density, and viscosity of light hydrocarbon/bitumen mixtures. The generalized correlations were developed using symbolic regression based on genetic programming and employing a 10-year set of comprehensive phase behavior experimental studies conducted under the SHARP research program on solvent-aided thermal recovery of bitumen. The data set comprised Surmont, JACOS, Mackay River, and Cold Lake bitumen samples and five light hydrocarbon solvents including methane, ethane, propane, n-butane, and n-pentane. The developed correlations are valid for gaseous solvents. Finally, the developed correlations for solubility, density, and viscosity were validated against a large data set of experimental measurements collected from the literature. The validation demonstrates that the developed correlations are able to accurately predict the available experimental data of solubility, density, and viscosity reported in the literature.

Mechanistic modelling of non-equilibrium interphase mass transfer during solvent-aided thermal recovery processes of bitumen and heavy oil

One of the important mechanisms involved in solvent-aided thermal recovery processes is interphase-mass transfer phenomenon. However, in current reservoir simulation models a local equilibrium is commonly assumed such that a simulation grid block is at instantaneous equilibrium. The assumption of local equilibrium often fails at larger scales or in situations where flow velocities are considerable compared to that of mass or heat transfer which results in significant discrepancies between reservoir simulation predictions and field scale observations. In this work, solvent-aided gravity drainage of bitumen was simulated with propane as a solvent. The effect of non-equilibrium mass transfer was included in the model to simulate the process using a kinetic approach. The results show that the assumption of the local instantaneous equilibrium results in lower oil recovery for the typical field scale simulation models. The analysis shows that this mismatch can be mitigated fairly through the inclusion of the non-equilibrium interphase mass transfer. Correlations for the non-equilibrium interphase mass transfer coefficients for propane/bitumen mixture were developed which can be used as guidelines for field scale modeling of solvent-aided thermal recovery processes.

New Solubility and Viscosity Measurements for Methane–, Ethane–, Propane–, and Butane–Athabasca Bitumen Systems at High Temperatures up to 260 °C

One of the important mechanisms in solvent-aided thermal recovery processes is viscosity reduction due to dissolution of solvent in the bitumen. This dissolution occurs either with the condensed solvent at the edge of the steam chamber or with direct contact of gaseous solvent and bitumen. Therefore, it is essential to determine the solubility and viscosity of solvent in bitumen for reservoir simulation of solvent-aided thermal recovery processes. We report new experimental viscosity and solubility data of methane–, ethane–, propane–, and butane–Athabasca bitumen systems at high temperatures (up to 260 °C). The experimental measurements have been conducted under liquid–vapor equilibrium conditions. Peng–Robinson Equation of State (PR-EoS) was employed to model the solubility data. The tuned PR-EoS represented the experimental solubility data of methane, ethane, propane, and n-butane in bitumen with absolute average relative deviations of 5.7, 4.1, 7.8, and 4.9%, respectively. The reported data find applic...

A new analytical model for estimation of the molecular diffusion coefficient of gaseous solvents in bitumen – Effect of swelling

Diffusion of gaseous solvents in bitumen is one of the imperative factors in studying solvent-aided thermal recovery processes. Experiments have shown significant swelling of bitumen upon diffusion of some gaseous solvents. Among different techniques for measurement of diffusion coefficient, Pressure Decay methods are the most popular. In one approach, liquid is placed in a cell overlaid by a gas cap. Diffusion of gas into the liquid at constant cell pressure can be achieved by continuously supplying the makeup gas into the gas cap. Different analytical and numerical models to estimate the molecular diffusion based on the mass of the injected gas have been proposed in the literature. However, there are two drawbacks associated with the previous models: 1) most of these models have been developed based on a no-swelling assumption while experiments have shown the significant swelling of bitumen upon diffusion of some solvents; 2) the models that incorporate the effect of swelling are numerical or semi-analytical and they are computationally-expensive, not straightforward, and prone to numerical error. Therefore, there is need for a simple analytical model that not only includes the swelling effect, but also is easy to implement. This study presents a novel analytical model obtained based on similarity solution along with a simple graphical method to estimate diffusion coefficients of gases in liquids. The experimental data of a moving interface as a result of swelling is used as an input to the developed model to estimate the diffusion coefficient. The developed model is applied to the available data in the literature and the predicted diffusion coefficients are compared to the previously reported ones. Moreover, the presented model is used to interpret new experimental data of nC4-nC10 system to estimate the molecular diffusion coefficient. The developed model and the experimental data find applications in design and optimization of solvent-aided thermal recovery of bitumen and heavy oils.

Experimental and modeling studies of water, light n-alkanes and MacKay River bitumen ternary systems

Water plays an important role as energy carrier in the solvent-aided thermal recovery processes of heavy oil and bitumen. The effect of water on phase behaviour of bitumen and solvent (light n-alkanes) mixtures is often ignored in thermal reservoir simulation. In this work, the effect of the presence of water on the phase behaviour of solvent in bitumen is studied. The solubility of solvents in bitumen as well as the density and viscosity of the bitumen rich phase are measured in both the presence and the absence of water. Results show a remarkable effect of water on solvent solubility in bitumen especially at high temperature conditions (T>150°C). A three-phase equilibrium calculation of the water-solvent-bitumen ternary system is carried out using a Peng-Robinson equation of state (PR-EoS) coupled with Henry’s constant. The results show that the PR-EoS regenerates the ternary system with acceptable accuracy. The density and viscosity of the bitumen rich phase in the presence of water are correlated using the experimental binary data.

Selection of efficient solvent in solvent-aided thermal recovery of bitumen

In solvent-assisted thermal recovery of bitumen, steam and solvent transfer their latent heat to the oil sands, mobilize the bitumen and co-condense on steam-bitumen interface. The mixing of heated bitumen with solvents further reduces its viscosity and the mobilized oil drains by gravity toward the production well. Co-injection of steam and solvent results in a gravitationally unstable diffusive boundary layer leading to convective dissolution of bitumen and solvent and thereby increases the oil recovery. We present a linear stability analysis to study the growth of convective instabilities and determine the onset of convective dissolution and the initial wavelength of instabilities. The scaling relations obtained from the linear stability are used to find the optimum solvent for solvent-aided thermal recovery processes by taking into account the azeotropic nature of solvent and steam co-condensation. The results show that an n-alkane carbon number range between 7 and 9 leads to earlier onset of convective dissolution, which is in agreement with the results of reservoir simulations. This study provides a fast screening method for selection of efficient solvent for the solvent-aided thermal recovery processes. In addition, the predicted initial wavelengths of instabilities facilitates selection of the proper grid size in numerical simulation of solvent and steam recovery processes.

An Optimal Operation Strategy of Injection Pressures in Solvent-aided Thermal Recovery for Viscous Oil in Sedimentary Reservoirs

Injection pressure is a key control parameter, which determines the amount of solvent and steam mixture consumed and its optimum level dominates the economic efficiency of solvent-aided thermal recovery in oil sands reservoirs. The authors determine the optimal strategy of determining operating pressures to achieve the maximum economic value; the scheme is based on an artificial neural network (ANN). The multilayer perceptron using backpropagation minimizes the objective value including bitumen production, steam injection, solvent retention, commodity price, and manufacturing cost. The numerical approach integrating with ANN results in accurate prediction similar to the time-consuming reservoir simulation. The application to the Athabasca oil sands reservoir confirms the enhanced results compared with the constant injection scenario and proposes the optimal schedule of injection pressures that repeats the increment and the decrement until reaching the same pressure level between the injection and the production well. This model maintains the consistency of the peak production rate on account of latent heat despite reducing the cycle amplitude. The developed model could be applicable to economically designed injection scenarios without any modification of production facilities.