Expanding Solvent Steam Assisted Gravity Drainage Research Articles

Measurements and PR EoS Modeling of Thermophysical Properties at Vapor-Liquid Equilibrium Conditions for Natural Gas Condensate/Live Bitumen Mixtures.

In response to the need for less energy-intensive and greener bitumen recovery techniques, the use of multicomponent diluents through the expanding solvent steam-assisted gravity drainage (ES-SAGD) technique has garnered significant interest in recent years. In this work, we report new comprehensive measurements and Peng-Robinson equation of state (PR EoS) modeling of thermophysical properties (saturation pressure, density, viscosity, and K-values) of multicomponent mixtures of methane-bitumen-solvent. The multicomponent solvent is a natural gas condensate comprised of C3, i-C4, n-C4, i-C5, n-C5, C6, and C7+. Density, viscosity, solubility, and K-values of live bitumen (bitumen with dissolved methane) and various multicomponent mixtures are measured in the pressure range of 1-4 MPa and the temperature range of 313.41-459.10 K. A systematic approach is utilized to model the measured data. The experimental data show that the saturation pressure of the live bitumen can be controlled by selecting an appropriate solvent (condensate) composition. Condensate also has a significant effect on reducing the density and viscosity of the system. The results also show that the K-values of the components are almost independent of the composition of the solvent. The new comprehensive data set and the EoS model parameters reported in this work find applications in reservoir simulation as well as the design and optimization of the ES-SAGD process.

In-situ solvents generation enhanced steam assisted gravity drainage (ISSG-SAGD): A low carbon and high-efficiency approach for heavy oil recovery

The primary bottleneck in heavy oil production lies in the significant energy consumption and CO2 emissions associated with steam injection for recovery. To address this challenge, we propose the ISSG-SAGD (in-situ solvent generation enhanced steam assisted gravity drainage) technique. The recovery mechanisms and operational strategies are investigated using a numerical simulation with an Athabasca bitumen reservoir model, affirming the considerable environmental and economic potential of ISSG-SAGD. The results demonstrate that ISSG-SAGD integrates the recovery mechanisms of both SAGP (steam and gas push) and ES-SAGD (expanding solvent SAGD). Moreover, employing cyclic steam injection, maintaining low operating pressure, and initiating ISSG-SAGD at an early stage enable a 33.79 % reduction in steam consumption, a 39 % decrease in average carbon intensity, a 5.40 % increase in oil production, and a 61.28 % rise in net present value compared to conventional SAGD. This study proves that the ISSG-SAGD approach offers a sustainable and efficient alternative for future heavy oil recovery endeavors, addresses the challenges of high energy consumption and carbon emissions, and paves the way towards a green and economically viable future for the heavy oil development.

Introduce dimethyl ether (DME) as a solvent for steam-assisted gravity drainage (SAGD) co-injection: An effective and environmental application

Conventional heavy oil and bitumen thermal recovery is currently facing increasing energy demands and climate-related challenges. Dimethyl ether (DME) as a renewable and sustainable solvent was recently proposed as a possible solution for a carbon transition to hydrogen economics. However, only limited studies with unclear mass transfer mechanisms have been conducted on DME and its co-injected on steam-assisted gravity drainage (SAGD) optimization. In this study, a numerical model was developed to investigate the DME-based expanding-solvent SAGD (ES-SAGD) process to capture the complex mechanisms involved. The impact of temperature on relative permeability curves and coupled heat/mass transfer were further discussed in detail. The results of DME-based ES-SAGD and conventional SAGD were compared in terms of process performance and energy efficiency as well as carbon intensity. The optimal range of DME concentration was investigated to achieve the highest recovery factor, and with the assistance of DME carbon intensity can be reduced to one quarter to half of that in conventional SAGD. The study confirmed DME is a novel solvent that leads to the viable performance of ES-SAGD to meet carbon emission reduction objectives.

Bitumen Recovery Performance of SAGD and Butane- and Hexane-Aided SAGD in the Presence of Shale Barriers.

Oil and gas formations are commonly found to be heterogeneous, and one of the most common occurrences of reservoir heterogeneity is the presence of shale barriers. Shale barriers typically have very low permeability and high initial water saturation. Due to low permeability, these barriers obstruct the oil drainage path, specifically in thermal recovery methods such as steam-assisted gravity drainage (SAGD). In addition to flow assistance, they also lead to heat losses due to absorption by the high initial water saturation. Expanding solvent steam-assisted gravity drainage (ES-SAGD) is a hybrid technique comprising solvent co-injection along with steam. Solvent being in the vapor phase can potentially overcome the restricted path due to the presence of shale barriers. This paper presents a numerical simulation study on comparison between SAGD and ES-SAGD in the presence of shale barriers. SAGD and ES-SAGD with hexane and butane are numerically simulated for 240 lognormally generated shale realizations. First, both recovery processes are analyzed over the whole simulation period. Additionally, they have also been evaluated at multiple cumulative steam oil ratio cut-offs at 2, 2.5, 3, and 3.5. Transition points are defined and explained to cluster the shale density/fractions based on similar behaviors. It was shown that the oil that cannot be mobilized and produced by SAGD because shale barriers can be reached by the vaporized solvent through tortuous paths and recovered. Also, thermal losses are reduced because of lower steam chamber temperature. This led to efficient results for ES-SAGD over SAGD in heterogeneous formations.

Rich solvent - Steam assisted gravity drainage (RS-SAGD): An option for clean oil sands recovery processes

The impact of steam generation on Steam-Assisted Gravity Drainage (SAGD) process economics and environmental impacts have led to various modifications of SAGD including solvent co-injection with steam. One example is the Expanding Solvent Steam-Assisted Gravity Drainage (ES-SAGD) process where 1–5 vol% solvent is injected with the steam into the reservoir. The solvent travels with the steam to the edge of depletion chamber dissolving into the oil thereby mobilizing the oil more than would have been achieved with heating alone. This means lower steam-to-oil ratio and thus, greater thermal efficiency, lower emissions intensity, and water consumption intensity. However, processes where the majority of the fluid injected is steam are still overly emissive and expensive to operate. There is a need to develop carbon-neutral bitumen production processes. Rich Solvent-SAGD (RS-SAGD) aims at injecting mostly solvent into the reservoir with small amounts of steam to achieve radically lower emissions and water consumption intensities than that of SAGD. Here, a RS-SAGD process is investigated where the solvent content is >60 vol% by using detailed thermal-solvent reservoir simulation in an Athabasca oil sands reservoir. The results reveal that RS-SAGD yields higher oil rate than that of SAGD and the process has significantly higher energy efficiency, up to 96% lower emissions and water consumption intensities than that of SAGD. Given the performance of RS-SAGD processes, oil sands operators should consider such processes for future operations.

Rising-phase performance evaluation of Expanding-Solvent SAGD: Considering the horizontal-wellbore effect

Expanding-Solvent Steam-Assisted Gravity Drainage (ES-SAGD) is proposed to develop the oil sands more efficiently than conventional SAGD. Even in the rising phase when the steam hasn't reached the overburden, the heat-mass transfer in the wellbore can be one of the reasons for the non-uniform chamber growth of ES-SAGD along the horizontal well. Furthermore, the time and oil production during the rising phase greatly determine the final benefits of the ES-SAGD. In this study, a mathematical method is established to evaluate the performance of ES-SAGD in the rising phase. The calculated results show that: pentane can help increase the oil rate in the rising phase significantly, while the effect of heptane is not quite obvious. Although propane is also a widely used solvent, the oil rate with it is even lower than that of conventional SAGD. The differentials between the cases, which consider the wellbore or not, is different for different solvent-steam co-injections. Specifically, the oil rate differential between the situations considering the wellbore effect or not for propane-SAGD is the highest and is almost twice that of conventional SAGD which has the least differential. Pentane-SAGD has the second-largest differential which is followed by heptane-SAGD. Therefore, for the sake of a more accurate evaluation of ES-SAGD performance in the chamber rising phase, the effects of solvent diffusion into the bitumen and the heat-mass transfer in the wellbore should be comprehensively considered.

Quantification of Phase Behavior for Solvent/Heavy-Oil/Water Systems at High Pressures and Elevated Temperatures with Dynamic Volume Analysis

SummaryAccurate quantification of phase behavior of solvent/heavy-oil/bitumen/water systems at high pressures and elevated temperatures is of high significance for the design of vapor extraction, cyclic solvent injection, expanding-solvent steam-assisted gravity drainage (ES-SAGD), and hot-solvent injection processes. The relevant experimental data and theoretical analyses are still insufficient for achieving a reliable model. This is especially true when the system temperatures approach or exceed the critical temperatures of the solvents used (i.e., when the solvent density is large enough).This study provides new experimental measurements of the phase behavior of propane (C3H8)/carbon dioxide (CO2)/heavy-oil/water systems at pressures up to 20 MPa and temperatures up to 432.3 K. More specifically, four feeds of C3H8/CO2/heavy-oil/water systems are used to conduct constant composition expansion (CCE) tests, during which the heights of the entire fluid system (i.e., total volume) and each phase are recorded at each pressure and temperature, respectively. Theoretically, a dynamic volume analysis (DVA) of the measured data is proposed for the first time to quantify each phase, provided that the assumption for vapor phase is valid and that the vapor and oleic phase densities can be accurately calculated. By tuning the binary interaction parameter (BIP) for solvent/heavy-oil pairs (denoted as BIPS−HO) to match the total volume, the height of the vapor/oleic (V/L) interface can be matched as well. By using the tuned BIPS−HO, the total volume and height of the V/L interface of C3H8/CO2/heavy-oil/water systems can be accurately predicted, no matter whether the solvent solubility in water is low (i.e., C3H8) or high (i.e., CO2). This DVA can be used to determine/evaluate the solvent solubility, saturation pressure/phase boundary, and phase volume/density accurately in a large temperature and pressure range. The newly proposed DVA method is also used to reproduce the experimental measurements collected from the literature, including phase-volume fractions, solvent solubility, and saturation pressure. In addition, the DVA method can serve as a tool to check whether the experimental measurements are reliable or not.

Data-Driven Models to Predict Hydrocarbon Production From Unconventional Reservoirs by Thermal Recovery

AbstractIn the numerical simulations of thermal recovery for unconventional resources, reservoir models involve complex multicomponent-multiphase flow in non-isothermal conditions, where spatial heterogeneity necessitates the huge number of discretized elements. Proxy modeling approaches have been applied to efficiently approximate solutions of reservoir simulations in such complex problems. In this study, we apply machine learning technologies to the thermal recovery of unconventional resources, for the efficient computation and prediction of hydrocarbon production. We develop data-driven models applying artificial neural network (ANN) to predict hydrocarbon productions under heterogeneous and unknown properties of unconventional reservoirs. We study two different thermal recovery methods—expanding solvent steam-assisted gravity drainage for bitumen and in-situ upgrading of oil shale. We obtain training datasets by running high-fidelity simulation models for these two problems. As training datasets of ANN models, diverse input and output data of phase and component productions are generated, by considering heterogeneity and uncertainty. In the bitumen reservoirs, diverse permeability anisotropies are considered as unknown properties. Similarly, in the oil shale reservoirs, diverse kerogen decomposition kinetics are considered. The performance of data-driven models is evaluated with respect to the position of the test dataset. When the test data is inside of the boundary of training datasets, the developed data-driven models based on ANN reliably predict the cumulative productions at the end of the recovery processes. However, when the test data is at the boundary of training datasets, physical insight plays a significant role to provide a reliable performance of data-driven models.

Steam-Oil Ratio in Steam-Solvent Coinjection Simulation for Homogeneous and Heterogeneous Bitumen Reservoirs

This research presents a mechanistic analysis of expanding-solvent steam-assisted gravity drainage (ES-SAGD) for heterogeneous reservoirs in terms of cumulative steam-oil ratio (SOR) as a function of cumulative bitumen production. Simulation case studies for SAGD and ES-SAGD with normal hexane at 35 bars are conducted for geostatistical realizations of two types of heterogeneous Athabasca-bitumen reservoirs. For the first type, low-permeability mudstone barriers are oriented horizontally. For the second type, they are inclined and more representative of the middle McMurray member. The solubility of water in the oleic phase at elevated temperatures is properly modeled to ensure reliable comparison between steam-assisted gravity drainage (SAGD) and ES-SAGD. Simulation results show that ES-SAGD is less sensitive to heterogeneity than SAGD in terms of cumulative SOR. On average, the reduction in SOR due to steam-solvent coinjection is simulated to be greater under heterogeneity. The reduction in SOR is greater for reservoir models with inclined mudstone barriers than in those with horizontal mudstone barriers. Analysis of simulation results indicates that the injected solvent tends to accumulate more significantly under heterogeneity, which enhances the mechanisms of ES-SAGD, such as dilution of bitumen by solvent and reduced thermal losses to the overburden. Tortuous hydraulic paths and slower gravity drainage under heterogeneity enhance the mixing between solvent and bitumen in the transverse direction along the edge of a steam chamber. Then, a larger amount of the accumulated solvent tends to facilitate lower temperatures near the chamber edge.

Mechanistic simulation study of expanding-solvent steam-assisted gravity drainage under reservoir heterogeneity

Expanding-solvent steam-assisted gravity drainage (ES-SAGD) is a potential method to reduce steam-oil ratio (SOR) of SAGD, which is a critical concern especially for highly-heterogeneous reservoirs. The main objective of this research is to investigate the flow characteristics of heterogeneous reservoirs in which solvent is more likely to lower SOR of SAGD.SAGD and ES-SAGD with normal hexane are simulated for fifty geostatistical realizations consisting of clean sand and shale, qualitatively representative of the middle member of the McMurray formation. Thermodynamic models are calibrated with experimental phase behavior data for reliable comparison between SAGD and ES-SAGD, including the water solubility in oil at elevated temperatures.Results show that the SOR reduction by steam-solvent coinjection is positively correlated with the increase in SAGD's SOR due to heterogeneity. Enhancement of bitumen flow by dilution is more important for lowering SOR for those reservoirs in which the permeability variation makes slow-flow regions during SAGD.Simulation results show that a larger amount of bitumen tends to be diluted by solvent in those reservoirs for which SAGD exhibits slow production of bitumen. Then, the observed results are analyzed by use of SAGD analytical equations that clarify several influential factors for bitumen flow beyond the edge of a steam chamber. It is shown that dilution of bitumen by solvent in steam-solvent coinjection becomes more significant where flow barriers limit the local bitumen flow under SAGD even at high temperatures. In such slow-flow regions, the bitumen flow rate can be substantially increased by accumulation of solvent in ES-SAGD, which reduces the oleic-phase viscosity and increases the oleic-phase saturation and, therefore, relative permeability. Solvent accumulation within a steam chamber can also reduce thermal losses because of lower operating-chamber temperatures.

A thermodynamic model to predict propane solubility in bitumen and heavy oil based on experimental fractionation and characterization

Propane has been suggested as suitable solvent for solvent-aided bitumen recovery methods such as Vapour Extraction (VAPEX), N-Solv (hot solvent injection), and Expanding Solvent-Steam Assisted Gravity Drainage (ES-SAGD). Characterization of bitumen and phase behaviour study of solvent/bitumen systems are the initial steps towards an optimized and successful solvent-aided bitumen recovery process. In this study, Athabasca bitumen is experimentally fractionated to four cuts using modified vacuum distillation and then each cut is characterized. The phase behaviour data including solubility, density, and viscosity of propane/bitumen cuts are measured in wide ranges of temperature and pressure. Using the measured solubility data of propane/bitumen cuts, the PR-EoS is tuned and a binary interaction parameter correlation between propane and bitumen components is developed. The bitumen is then characterized using the boiling point or carbon number distribution obtained by Simulated Distillation test (ASTM D7169). The generalized model is then implemented to calculate the propane solubility in two bitumen samples from different reservoirs (Athabasca and Cold Lake). Our proposed model in this paper, predicted the propane solubility in Athabasca bitumen sample with an average deviation of 1.8 mol.% without using any experimental data of propane/bitumen system or tuning parameter. The proposed model was also evaluated by predicting the propane solubility in Cold Lake bitumen. The propane solubility in Cold Lake bitumen was calculated with an average deviation of 3.0 mol.%, which shows the generality of the proposed model.

Technology Focus: EOR Performance and Modeling (January 2018)

Technology Focus Efforts for increasing recovery factors in all reservoir types continued with increasing momentum during the past year. Maturing fields combined with limited exploration forced operators to focus on recovering more from existing fields. Implementing enhanced oil recovery (EOR) in a depressed-oil-price environment is accepted as a challenge by our resilient industry, and, therefore, all aspects of EOR, including EOR agents, EOR physics, and EOR modeling and monitoring, improved further. We saw progress in all EOR schemes in the past year, from expanding-solvent steam-assisted gravity drainage (SAGD) to increasing recovery factors in unconventional fields in the US. While carbon-dioxide EOR continues to be used in conventional reservoirs, it is also becoming a desired EOR agent for unconventionals. EOR implementations in high-viscosity-oil reservoirs continued to see improvements with more chemistry, with heat, with improved reservoir characterization, and with advancements in SAGD implementation. Progress in chemical EOR, from polymer to alkaline/surfactant/polymer, has been significant. Not only are there new chemicals with improved recovery capabilities, but also the cost of the chemicals is being reduced continuously. All those factors led to more operators using chemical EOR. It is worth reiterating that increasing recovery factors in unconventionals will remain the top priority for many years to come. The next chapter of the exciting unconventionals journey will be more about EOR. EOR momentum on all fronts is reflected in the technical papers reviewed this year. This is the first time I have seen that all EOR schemes were covered. Half the technical papers were about fundamentals, and the other half were about field implementation. I found that to be the best indicator that EOR is becoming an integral part of managing oil fields. The selected papers provide a summary of some of the noteworthy advancements in EOR performance and modeling. Recommended additional reading at OnePetro: www.onepetro.org. SPE 187032 Nanoscale-Flow-Chip Platform for Laboratory Evaluation of Enhanced-Oil-Recovery Materials by Michael Engel, IBM Research, et al. SPE 185526 Surveillance and Initial Results of an Existing Polymer Flood: A Case History From the Rayoso Formation by L.A. Martino, YPF, et al. SPE 183165 Borehole Controlled-Source Electromagnetics for Hydrocarbon-Saturation Monitoring in the Bockstedt Oil Field, Onshore Northwest Germany by K. Tietze, GFZ Potsdam, et al. SPE 182669 Uncertainty Quantification for Foam Flooding in Fractured Carbonate Reservoirs by A. Almaqbali, Heriot-Watt University, et al. SPE 185002 ES-SAGD Relative Permeability as a Function of Temperature and Solvent Concentrations by M. Zeidani, University of Calgary, et al.

The effect of different solvents on the density of undersaturated athabasca bitumen: Application in VAPEX and ES-SAGD

ABSTRACTPredicting the density of bitumen after solvent injection is highly required in solvent-based recovery techniques like expanding solvent-steam assisted gravity drainage (ES-SAGD) and vapor extraction (VAPEX) in order to estimate the cumulative oil recovery by these processes. Using experimental procedures for this purpose is so expensive and time-consuming; therefore, it is crucial to propose a rapid and accurate model for predicting the effect of various solvents on the dilution of bitumen. In this study, an adaptive neuro-fuzzy interference system is introduced to estimate the effect of methane, ethane, propane, butane, carbon dioxide, and n-hexane on the density of undersaturated Athabasca bitumen in wide ranges of operating conditions. The obtained results were in an excellent agreement with experimental data with coefficients of determination (R2) of 0.99997 and 0.99948 for training and testing datasets, respectively. Statistical analyses illustrate the superiority of the proposed model in predicting the bitumen density at different conditions.

Experimental and numerical study of the convective mass transfer of solvent in the Expanding-Solvent SAGD process

In the Expanding-Solvent Steam-Assisted Gravity Drainage (ES-SAGD) process, the mass transfer of the dissolved solvent in the steam chamber boundary is critical to the oil production performance. In this study, experimental and numerical simulation approaches are used to investigate the gravity-driven convective movement of solvent in the steam chamber boundary in ES-SAGD. The experiments are conducted in a two-dimensional (2-D) sandpack model, in which a sloping gas-liquid interface in a closed system is developed as an analog of the steam chamber boundary in ES-SAGD. Thus, the flow along the sloping gas-liquid interface is used to represent the flow in the steam chamber boundary in ES-SAGD. Solvent mass transfer is observed by its concentration variation in the direction perpendicular to the flow surface. Later, CMG STARS is used as the simulator to execute the numerical simulations, and the simulation successfully captured the experimental results. In this study, the findings demonstrate the existence of convective solvent movement along the sloping gas-liquid interface. Furthermore, the results show that there is accelerated solvent movement along the interface under high permeability, and slow movement along the interface under high flow rate and high fluid viscosity. Diffusion and dispersion are tested by varying the corresponding coefficients in the physical and numerical models, and results show that these phenomena have negligible effect on the transverse solvent mass transfer process. This study found that gravity-driven convection is the dominant mechanism of solvent mass transfer in the steam chamber boundary in ES-SAGD.

Quick Screening of Pareto-Optimal Operating Conditions for Expanding Solvent–Steam Assisted Gravity Drainage Using Hybrid Multi-Objective Optimization Approach

Solvent–steam mixture is a key factor in controlling the economic efficiency of the solvent-aided thermal injection process for producing bitumen in a highly viscous oil sands reservoir. This paper depicts a strategy to quickly provide trade-off operating conditions of the Expanding Solvent–Steam Assisted Gravity Drainage (ES-SAGD) process based on Pareto-optimality. Response surface models are employed to evaluate multiple ES-SAGD scenarios at low computational costs. The surrogate models play a role of objective-estimators in the multi-objective optimization that provides qualified ES-SAGD scenarios regarding bitumen recovery, steam–energy efficiency, and solvent-energy efficiency. The developed hybrid approach detects positive or negative correlations among the performance indicators of the ES-SAGD process. The derived Pareto-optimal operating conditions give flexibility in field development planning and thereby help decision makers determine the operating parameters of the ES-SAGD process based on their preferences.

Analysis of adaptive grid refinement technique for simulations of ES-SAGD in heavy oil reservoirs

The intrinsic advantages of hybrid steam-solvent or solvent-based thermal recovery methods for heavy oil include faster oil production, higher ultimate recovery factor, reduction of energy, and water treatment expenses, better control of GHG emission. Light hydrocarbon injection implies improved heavy oil mobilization, steam and solvent condensation, solvent to oil mixing, and oil viscosity effect at moderate temperature. Typically, field-scale reservoir simulation models are built on numerical grids with cell sizes making practically difficult accurate description of heat and mass transport at the edge of the gas chamber. Outside this zone, this typical grid can be acceptable. The adaptive grid refinement may offer a compromise solution if the numerical model accepts the necessary degree of refinement. In our current work, we present a methodology of large-scale numerical simulations for so-called expanding solvent SAGD (ES-SAGD) processes using adaptive dynamic gridding at different degrees of the refinement. The adaptive grid refinement is a Cartesian grid amalgamation process based on threshold values of predefined trigger variables. Comparison is performed between oil production mechanism interactions for typical Athabasca bitumen and illustrated with temperature and solvent concentration fields for different discretization sizes. Good adaptive grid refinement results have been obtained for the models based on adaptive implicit approach with high refinement degree, in heterogeneous reservoir (at relatively small correlation length) in vertical 2D cross-section. The numerical performance aspects including the CPU time analysis with and without the use of dynamic gridding are presented in some detail.

Solubility and thermo-physical properties measurement of CO2- and N2-Athabasca bitumen systems

The production of heavy oil and bitumen is more complex and expensive than conventional oils. One of the main reasons is that heavy oils and bitumen have high viscosity and are usually immobile at the reservoir conditions. The viscosity of heavy oil or bitumen must be lowered in order to be recoverable by an oil recovery method such as solvent injection, steam-assisted gravity drainage (SAGD), and expanding solvent SAGD (ES-SAGD). In this study we report thermo-physical properties of CO2 and N2/bitumen mixtures. Solubility of non-condensable gaseous solvents, i.e. carbon dioxide and nitrogen, in Athabasca bitumen, as well as the liquid phase density and viscosity of solvent saturated bitumen are measured at temperatures up to 190°C and pressures up to 8MPa. Moreover, Peng-Robinson equation of state (PR-EoS) is applied to represent the experimental solubility which shows the absolute average relative deviation (AARD) of 4.3% and 7.6% for CO2 and N2, respectively. These findings will find many applications in the design and simulation of heavy oil and bitumen recovery processes.

An Experimental Study of Multiphase Behavior for n-Butane/Bitumen/Water Mixtures

Summary Steam/solvent coinjection has been studied and pilot tested as a potential method to improve steam-assisted gravity drainage (SAGD) for bitumen recovery. Reliable design of coinjection requires reliable pressure/volume/temperature (PVT) data for bitumen/solvent/water mixtures, which are scarce and fragmentary in the literature. The main objective of this research was to present a new set of PVT and multiphase data for n-butane/Athabasca-bitumen/water mixtures at pressures up to 10 MPa and temperatures up to 160°C. Experiments were conducted with a conventional PVT apparatus. The data presented include multiphase equilibria up to four coexisting phases and liquid densities for 100% bitumen, two mixtures of n-butane/bitumen, and one mixture of n-butane/bitumen/water. Liquid/liquid separation of hydrocarbons was experimentally observed at the n-butane concentration of 97 mol% in the n-butane/bitumen system with/without water, for a wide range of temperatures at operating pressures for expanding-solvent SAGD (ES-SAGD). This may indicate the limited solubility of n-butane in bitumen even when a high level of accumulation of n-butane takes place near a chamber edge in ES-SAGD for Athabasca bitumen. The multiphase transition that involves appearance/disappearance of the vapor phase was observed to occur near the vapor pressure of n-butane or its extension. Such phase transition occurs at a higher pressure in the presence of water, because of its vapor pressure, than in the absence of water at a given temperature. This is the first time four coexisting phases are reported for n-butane/Athabasca-bitumen/water mixtures at temperature/pressure conditions relevant to ES-SAGD.

Compositional Mechanisms in Steam-Assisted Gravity Drainage and Expanding-Solvent Steam-Assisted Gravity Drainage With Consideration of Water Solubility in Oil

Summary Experimental data have shown that the solubility of water in the oleic (L) phase (xwL) can be significant at elevated temperatures. However, xwL was not properly considered in prior studies of steam-assisted gravity drainage (SAGD) and expanding-solvent (ES)-SAGD. The main objective of this research is to present a detailed study of compositional mechanisms in SAGD and ES-SAGD simulation by considering xwL. The phase-behavior models used in this research are carefully created on the basis of experimental studies presented in the literature. Mechanistic simulation studies are then conducted for SAGD and ES-SAGD. Coinjectants used in ES-SAGD simulations range from propane through n-decane. Results show that xwL enhances bitumen production in both SAGD and ES-SAGD, mainly because xwL results in reduction of L-phase viscosity. The enhancement is more significant when the chamber-edge temperature is higher, because xwL increases with temperature. The enhancement of bitumen production observed in the case studies is 7.66% for SAGD, 4.08% for n-C6-SAGD, and 4.85% for n-C8-SAGD for a fixed period of operation at 35 bar. It is important to consider xwL in SAGD and ES-SAGD simulations, because the performance of ES-SAGD relative to SAGD tends to be overestimated without considering xwL. A guideline is presented to leverage xwL to improve bitumen production in ES-SAGD. As discussed in our prior research, solvent becomes effective in diluting bitumen and reducing the steam requirement only when it sufficiently accumulates near the chamber edge. New results show that water can act as a diluting agent until solvent sufficiently accumulates near the chamber edge.

Cracked Naphtha Coinjection in Steam-Assisted Gravity Drainage

Steam-assisted gravity drainage (SAGD) is a thermal in situ recovery method for heavy oil and oil sands that has been employed to exploit the vast petroleum deposits in the Athabasca region of northern Alberta that are not amenable to surface mining. Nevertheless, in spite of its success in recovering highly viscous bitumen, SAGD remains a costly technology that requires large energy input in the form of steam for each barrel of produced oil. This requires large quantities of water and natural gas, resulting in sizable greenhouse gas (GHG) emissions and extensive postproduction water treatment. There are ongoing efforts to make SAGD more energy-efficient and environmentally sustainable by reducing steam consumption while maintaining favorable oil production rates and ultimate oil recovery. Such efforts include the coinjection of steam and solvent in a process called expanding solvent SAGD (ES-SAGD) wherein bitumen that is essentially immobile at initial reservoir conditions is made mobile by heating and m...