Steam Assisted Gravity Drainage Operations Research Articles

Analytical prediction model for edge water invasion flow rate in SAGD heavy oil reservoirs

SAGD (Steam Assisted Gravity Drainage) technology is a highly developed method for the extracting heavy oil. In the Liaohe Oilfield in China, there are 72 SAGD well groups within a massive heavy oil reservoir containing edge water and the risk associated with edge water invasion is substantial. Currently, the injected steam is less than 50 m away from the edge water, which increases the urgency to address the potential invasion of edge water. If the edge water flows into the reservoir, it will impact nearly 8.0 × 105 tons of crude oil production. Recognizing the importance of mitigating the edge water invasion, this paper proposes a prediction model for the edge water invasion flow rate in SAGD reservoirs. The model integrates mass and heat transfer dynamics between the steam chamber and edge water, the relative permeabilities of oil and water phases, and the viscosity-temperature relationship of water. The model is validated through numerical simulations and field data. The findings indicate that for SAGD reservoirs with a permeability greater than 1 D, maintaining a minimum distance of 25 m between the edge water and the steam chamber is advisable, especially when the pressure differential is 0.5 MPa. Furthermore, the prediction model is used to forecast the edge water breakthrough time and evaluate water invasion risk. A prediction chart for the edge water invasion flow rate is developed, providing a practical tool for estimating invasion flow rate curves. Also, a method of edge water invasion warning is established, with a corresponding chart that offers a quick assessment of water invasion risks in heavy oil reservoirs. Overall, this research lays a foundational framework for understanding and managing the edge water invasion in SAGD operations, offering critical insights for the future study aimed at addressing the challenge posed by edge water in heavy oil reservoirs.

Demulsification of steam-assisted gravity drainage (SAGD) emulsions under high temperature and high pressure: Effects of emulsion breaker and reverse emulsion breaker dosages

Effective treatment of complex emulsions formed during steam-assisted gravity drainage (SAGD) production is crucial for oil/water separation and subsequent processing. However, it remains challenging due to the complexity of SAGD emulsions, and there are only very limited studies on demulsification under simulated SAGD conditions. This study systematically characterized the comprehensive properties of a fresh field SAGD emulsion with about 84.6 % water and 15.4 % bitumen, and then achieved effective demulsification under a simulated SAGD condition at 135 °C and 60 psi via adding a poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) copolymer (as a model emulsion breaker or EB) combined with a branched polyethylenimine (PEI, as a model reverse emulsion breaker or REB) in a bench-scale bottle test setup. The effects of EB and REB dosages on the demulsification of the SAGD emulsion were evaluated based on the properties of the separated phases. Dynamic interfacial tension, zeta potential, and coalescence time were measured to reveal the demulsification mechanisms of EB and REB. The highly interface-active EB facilitated oil dehydration by displacing the natural interface-active species at the interfaces, disrupting the rigid interfacial films and promoting water droplet coalescence, while the cationic REB aided water de-oiling by neutralizing oil droplet surface charges, disrupting the rigid interfacial films and promoting the approach and coalescence of oil droplets in aqueous media. This work has improved the understanding of SAGD emulsion characteristics, the effects of EB and REB dosages on the demulsification performance, and the underlying demulsification mechanisms in SAGD operations. The results provide useful insights for developing effective and cost-efficient chemical approaches to address challenging emulsion issues in oil production.

Small modular nuclear reactors: A pathway to cost savings and environmental progress in SAGD operations

Small Modular Nuclear Reactors (SMRs) offer a promising option for environmentally friendly bitumen recovery operations. The extraction of oil sands in Western Canada is vital for the economy, but traditional methods like Steam-Assisted Gravity Drainage (SAGD) contribute significantly to greenhouse gas (GHG) emissions. In SAGD, steam generation, primarily fueled by natural gas combustion, is the main source of emissions. Given the imperative to reduce carbon intensity, less emissive recovery methods are needed to sustain production and economic viability in Canadian oil sands. Currently, there are limited non-carbon alternatives for steam generation in oil sands applications. The utilization of SMRs for steam generation presents a clean alternative. In this study, we examine the feasibility of employing SMRs in in-situ oil sands recovery operations. Through standardized economic metrics and sensitivity analysis, we demonstrate that integrating SMRs into SAGD operations eliminates GHG emissions significantly and can potentially outperform conventional natural gas-based steam generation in terms of net present value, under certain operational scenarios. Hence, our findings indicate that SMRs hold promise for decarbonizing oil sands recovery processes.

Study on Characteristics of Steam Chamber and Factors Influencing Nitrogen-Assisted Vertical–Horizontal Steam Drainage Development

With the notable achievements attained through the implementation of steam-assisted gravity drainage (SAGD), the vertical–horizontal steam drive (VHSD) emerges as a pivotal technological advancement aimed at significantly enhancing the efficiency of thin reservoir heavy oil recovery subsequent to steam cyclic stimulation. The inclusion of nitrogen assistance has proven effective in enhancing the efficacy of gravity drainage techniques in reservoir development. However, it is noteworthy that this method has only led to improvements in approximately 50% of the well groups within the observed field. The comprehensive evaluation index of VHSD was proposed, and as the objective function, it was determined that the greatest contribution to the VHSD technique lies in oil saturation, accounting for 40% of the overall evaluations. This differs from conventional SAGD operations, where reservoir thickness serves as the primary determinant. Building upon an enhanced physical simulation similarity criterion, two comparative injection scheme experiments were conducted to explore the impact of nitrogen injection on the performance of VHSD and the characteristics of the steam chamber. Nitrogen is distributed in the vicinity of the steam chamber, leading to the formation of a dual mechanism characterized by ‘top heat insulation and lateral traction’ on the steam chamber. The lateral traction accounts for approximately 25% of the team chamber volume. Additionally, the inducement of nitrogen causes a downward displacement of crude oil, resulting in its accumulation within the high-temperature region of the steam chamber. This, in turn, enhances the contact area between the high-temperature steam and the crude oil, ultimately leading to improvement in production efficiency. Further validation of the impact of nitrogen on steam lateral traction and interlayer steam drainage within the reservoir was confirmed using Xinjiang oilfield testing. The well temperature increased from 75 °C to 130 °C.

Characterization and acid treatment of silica and organics in evaporator blowdown wastewater arising from SAGD operations

The evaporator blowdown (EBD) wastewater from high-pressure steam generation for the steam-assisted gravity drainage (SAGD) bitumen extraction process contains elevated concentrations of dissolved inorganic and organic compounds, of which silica and organics pose challenges in its treatment and disposal. This study investigated treatment options for EBD before its disposal. Following detailed physical and chemical characterization of the EBD, we examined its acid treatment with HCl and H2SO4 at pHs ranging from 12 to 2. The acid treatment performance was evaluated in terms of silica and organic removal efficiencies along with the filtration rate and filtrate recovery. Both acids gave similar silica and organic removal efficiencies; however, the filtration performance following the HCl-treatment was better than the H2SO4-treatment. In practice, the acids would likely perform comparably with regard to silica removal and the final process selection would more likely be influenced by other factors such as storage, material compatibility, cost, and downstream or subsurface compatibility. The HCl-treatment was investigated further with both the EBD and prepared silica solutions for the silica removal efficiency and filtration performance. The experiments conducted at ∼20 °C demonstrated higher silica removal efficiencies at pHs 10 and 8, whereas higher organic removal efficiencies were obtained at pHs 4 and 2. The experiments conducted at ∼80 °C showed enhanced silica removal at pH = 8 and higher organic removal at pH = 2. The precipitated solids were characterized using XRD and ATR-FTIR spectroscopy to identify the minerals and functional groups. The XRD patterns demonstrated that the solids generated were amorphous. The ATR-FTIR spectra revealed the predominance of siloxane, silanol, carboxylate and carbonyl compounds. These results confirmed a substantial removal of silica and organic constituents from the EBD through the acid treatment process.

Impact of Inflow and Outflow Rate Control to Minimize Freshwater Usage: Historical Canadian Steam-Assisted Gravity Drainage Operations versus Numerical Simulations

Impact of Inflow and Outflow Rate Control to Minimize Freshwater Usage: Historical Canadian Steam-Assisted Gravity Drainage Operations versus Numerical Simulations

A Simple Normalized Analytical Model for Oil Production of SAGD Process and Its Applications in Athabasca Oil Sands

Summary Since the late 1980s, when the Alberta Oil Sands Technology and Research Authority Underground Test Facility project first demonstrated the feasibility of the steam-assisted gravity drainage (SAGD) technology, many commercial SAGD projects were brought online in Western Canada. Now, many of these projects have late-life SAGD wells approaching their ultimate SAGD recovery factors. Although these projects have demonstrated highly variable production performance, there is an opportunity to use the industry production data to find what they have in common and develop a normalized SAGD model. For this paper, we collected oil production history from several leading SAGD projects with late-life production in the Athabasca oil sands area and confirmed the three stages in an SAGD project lifespan: chamber rising, chamber spreading, and chamber falling stages. By normalizing the field data, all SAGD projects converged to one type curve, regardless of reservoir quality and operating conditions. Based on this observation, a new simple normalized model is derived to model the bitumen production in a typical SAGD process for Athabasca oil sands. The new model bridges the gap between the existing SAGD analytical model and conventional decline analysis and provides oil production forecasts based on the inputs for the five-component recovery factor method defined in the Canadian Oil and Gas Evaluation Handbook(Society of Petroleum Evaluation Engineers 2018). The model has been applied to one of the thermal projects to history match the field production. By running a Monte Carlo simulation, this model further demonstrates its capability to capture the uncertainty of the production forecast for the project at different stages of SAGD operation. In addition, by properly modifying the type curve of the analytical model, a similar workflow can be used to model cases with special reservoir quality or different operational limitations.

Sequentially Coupled Thermal-Hydraulic-Mechanical Simulation for Geomechanical Assessments of Caprock Integrity in SAGD

Oil sand reservoirs and caprock undergo deformations triggered by pore pressure increases and thermal induced stresses during the steam-assisted-gravity-drainage (SAGD) processes. Geomechanical assessments are mandated by energy regulators to evaluate the caprock integrity and ensure the safe SAGD operations. Commercial reservoir simulation packages started to incorporate geomechanical effects when predicting flow response; however, these geomechanical modules are not able to correctly model the plastic deformations caused by thermal-hydraulic-mechanical (THM) interactions, which has a first order effect on predicting steam chamber propagation and evaluating caprock integrity.
 An integrated coupled THM modeling methodology is proposed here to improve the modeling of reservoir deformations and caprock integrity in a heterogeneous oil sand reservoir with interbedded shale barriers. The pressure and temperature front are found to propagate at different speed and that dominate the elastic and plastic deformations caused by changes of shear and mean effective stress. Therefore, four stages are divided in the SAGD process that can be interpretations of changes in stress paths including buildup of pore pressure, generation and dissipation of thermal induced stresses. The response surfaces of minimum factor of safety (FOS) are introduced and computed to provide a conservative estimate for caprock integrity during SAGD of a heterogeneous reservoir with multiple layers of caprocks in Athabasca oil sands. 

On geothermal energy recovery from post-SAGD reservoirs

In the steam-assisted gravity drainage (SAGD) process, large amounts of steam are injected into the reservoir to mobilize bitumen for its production to surface. The amount of thermal energy injected into the reservoir creates a man-made geothermal system that could be used to yield heat after the SAGD operation is complete. In the research documented here, for the first time, the amount of energy stored in the reservoir is evaluated and potential processes for recovery of the thermal energy are explored. The results reveal that after 10 years of SAGD, about 35% of the total injected energy in the steam remains in the reservoir rock from which the bitumen was extracted. After a 1 year blowdown stage at the end of the SAGD operation, ∼32% of the total injected energy remains in the reservoir rock. Three cases are used to explore the potential for recovering the thermal energy in the reservoir rock. The results show that the best case is one where a new horizontal well is added at the top of the reservoir above the SAGD well pair. In this case, >100 °C water was recovered at high rate for over 1,400 days realizing about 34% recovery of the thermal energy contained in the reservoir rock after the SAGD blowdown stage. The results demonstrate that there is potential for recovering the thermal energy. This recovered energy offers means to make the SAGD process more thermally efficient over its entire energy production life.

A New Analytical Model for Predicting Steam-Assisted Gravity-Drainage Performance in the Plateau and Decline Stages

Summary Analytical models have been widely used to study the steam-assisted gravity-drainage (SAGD) process. Existing analytical models for this process either underperform or are limited in their applicability. In this paper, a new analytical model is developed to address these shortcomings. The new model consists of three major components. First, an equation for predicting oil production rate during the plateau stage was developed. This equation allows for permeability anisotropy in the reservoir, which is neglected in the majority of existing analytical models. Second, a novel and concise equation for calculating oil production rate during the decline stage was derived. This equation for the first time provides a general relationship between oil production rate during the decline stage and the properties of the reservoir together with key operating conditions and simultaneously mitigates the shortcomings of the majority of existing models (e.g., inapplicable in the decline stage of the SAGD process). Third, new correlations representing heat loss from the steam chamber to the overburden and heat transfer to oil-undepleted zone ahead of the chamber interface were derived; new predictive equations for estimating steam/oil ratio (SOR) in the plateau and decline stages of SAGD were obtained. The new model has been validated against a 2D scaled laboratory experiment and a set of field data. The results of this validation show that the new model predicts the oil production rate and SOR over the lifetime of an SAGD operation (excluding the short steam rise period) reasonably well. Predictions from the new model were also compared with several existing analytical models: The new model provided a closer match to actual measurements than other models. This robust model is grounded in more physics and incorporates reservoir geology and well operating conditions. It enables better understanding of the SAGD process and significantly improves the prediction of SAGD performance. Hence, it can be used to design new SAGD projects, predict existing projects, and optimize existing projects.

Subsurface waste heat recovery from the abandoned steam assisted gravity drainage (SAGD) operations

A considerable fraction of the energy injected during the thermal recovery of oil remains in the subsurface and wasted in the surrounding geological formations after the profitable life of oil wells is over. This work studied the concept of thermal energy extraction from the abandoned SAGD operations in oil sands reservoirs for generating electric power. The cold water is injected as a working fluid to extract heat after the oil production is ceased, and the produced hot water is fed to a surface binary cycle to generate electric power. The results show that an oil sands reservoir after SAGD operations could be regarded as an artificial geothermal system suitable for thermal energy extraction. It is demonstrated that a total net electric energy output of 57 GWh could be achieved based on a single SAGD well pair during a ten-year heat-extraction time, indicating the huge heat extraction potential at full field scale. The results show that the thermal energy conversion efficiency to electricity for the abandoned SAGD wells can reach as high as 12%. The demonstrated subsurface waste heat recovery from the abandoned SAGD sites revealed that between 15 and 36% reduction in CO2 emission could be achieved.

In situ stress field in the Athabasca oil sands deposits: Field measurement, stress-field modeling, and engineering implications

In situ stress is one of the key engineering parameters that ensures caprock integrity in steam-assisted gravity drainage (SAGD) operations. Massive steam injections during an SAGD operation leads to significant changes in the pore pressure, temperature, stress, and volumetric strain in the rock formations. These changes trigger deformation and stress redistribution in the overburdened strata, which could lead to a containment breach of the caprock through shear or tensile failure. To ensure subsurface steam containment, both to satisfy public safety considerations and instill confidence that the steam containment will continue over the necessary timescales, the Alberta government requires every SAGD operator to measure the in situ stress conditions in the oil sands reservoir and its caprock. Minifrac test is a suggested method that can measure the minimum principal stress with high confidence. A safety factor (SF) of 80% is used to determine the maximum operation pressure (MOP) for safe SAGD operations; in other words, MOP = 80%*σmin, where σmin is the minimum principal stress at the base of the caprock. In most cases, this 80% SF safeguards the SAGD injection pressure to always remain lower than the σmin at the base of the caprock, ensuring that no tensile fractures are initiated at the caprock.In this study, we compiled a database containing in excess of 100 minifrac datasets across the Athabasca oil sands region and constructed an in situ stress map. Based on our in situ stress dataset, we developed a quantitative risk model to analyze the effects of uncertainties on the probability of exceedance (i.e., the probability that the MOP exceeds the fracture pressure at the base of the caprock). The risk model involves defining probability distributions to quantify the uncertainties at the shallowest depth and minimum stress gradient. The output of the risk model was a set of predictions of exceedance probabilities, which were computed using Monte Carlo simulations. Through a statistical analysis of this in situ database and risk-based simulation analysis, this study demonstrates the reliability of a SF of 80%.

Numerical Modeling of the Steam Chamber Ramp-Up Phase in Steam-Assisted Gravity Drainage

Due to the critical nature of the ramp-up phase of an efficient steam-assisted gravity drainage (SAGD) process, it is important to understand the physics of the steam chamber ramp-up phase in order to improve SAGD production performance. In conventional numerical simulation models, the dynamics of the steam chamber ramp-up phase are not fully resolved because of unclear steam–oil–water interactions during the vertical growth of the steam chamber and how its state changes as the reservoir parameters vary. This work provides an efficient approach for the numerical modeling of the steam chamber ramp-up phase in an SAGD operation. The steam chamber ramp-up phase was fully examined through the consideration of the effects of the temperature-dependent oil–water–gas multiphase flow system and the vertical countercurrent flow. The simulation results revealed that for the large temperature gradient of the mobile oil zone at the edge of the steam chamber, a delicate temperature-dependent multiphase flow system was essential for the reliable estimation of the SAGD ramp-up phase. The vertical countercurrent flows of oil–gas and oil–condensate were the dominant mechanisms over cocurrent flow, which significantly impacted the steam chamber ramp-up rate. The numerical model physically predicted the steam chamber ramp-up phase and could be used to efficiently compute a field-scale simulation using a dynamic gridding function that was based on a fine grid model.

Treatment Technologies for Organics and Silica Removal in Steam-Assisted Gravity Drainage Produced Water: A Comprehensive Review

Produced water from steam-assisted gravity drainage (SAGD) operations is a complex mixture of inorganic and organic constituents. Silica, carbonate and bicarbonate, and hardness are three inorganic constituents of interest, whereas the organic contaminants are composed of free and emulsified oil (F&EO) and water-soluble organic (WSO) fractions. Although the current warm lime softening (WLS) and hot lime softening (HLS) in SAGD operations are able to remove particles, silica, and organics, improving the removal efficiency of organics and silica still faces technical and operational challenges given their complex chemistry in produced water. Much effort has been put toward developing effective and cost-efficient treatment processes to handle organics and silica. In this work, we have systematically reviewed the properties of silica and the characteristics of dissolved organics in SAGD produced water, as well as the working principle and removal mechanisms of several techniques, including membrane technology, adsorption, coagulation–flocculation, and hybrid processes. Different analytical techniques for characterizing dissolved organics have been assessed, and the dominant and representative organic species in produced water have been identified. The advantages and limitations, impact factors, application performance, and effectiveness of each technology have been discussed in terms of the removal efficiency for silica and organics. Some remaining challenges and perspectives for future research are also presented. This work provides an improved understanding of the characteristics of silica and organics in SAGD produced water, as well as different treatment technologies, with useful implications for developing effective, feasible, and cost-efficient treatment processes with the objective of enhancing the removal of silica and organics from produced water, thereby leading to economic and environmental performance improvements.

Policy Insights to Accelerate Cleaner Steam-Assisted Gravity Drainage Operations

The literature is replete with concerns on the environmental impact of steam-assisted gravity drainage (SAGD), but rigorous analysis of its improved environmental performance over the past 20 years remains unresolved, as well as the underlying technological reasons for this improvement. Here, we present an analysis of historical and future greenhouse gas (GHG) performance of SAGD operations in Alberta, Canada, considering for the first-time factors that affected technology deployment. Depending on the case, the results show a reduction of 1.4–24% of SAGD GHG intensity over the past 12 years. Improvements mainly arise from incremental changes adopted based on technical, environmental, socio-economic, and policy drivers. Considering these factors, we propose policy interventions to accelerate further reductions of GHG emissions. However, if similar behaviour from industry continues, anticipated GHG intensity reduction will range between 6.5–40% by 2030, leading to an intensity between 58 and 68 kgCO2e/bbl. It still remains unclear if in situ oil sands bitumen extraction will reach current conventional oil emission intensities. Thus, we suggest that the SAGD industry drastically accelerate its deployment of cleaner oil sands extraction technologies considering the policy insights proposed.

Bench-scale oil fouling/antifouling tests under high temperature and high pressure conditions and the underlying interfacial interaction mechanisms

Oil fouling is commonly encountered in many environmental and engineering fields and remains a challenging issue. The fouling issue in steam-assisted gravity drainage (SAGD) process for extracting bitumen from oil sands deposits has received much attention from oil industry. In view of low capital investment and exceptional antifouling performance, adding antifoulants has emerged as a promising strategy for addressing fouling issues. Developing an efficient method to evaluate their antifouling performance under production conditions is urgently needed. In this work, we report a novel bench-scale test method for quantitatively evaluating the antifouling performance of antifoulants under high temperature and high pressure (HTHP), close to SAGD operation conditions. The effects of antifoulant dosage and stirring rate on the antifouling performance are systematically investigated. The underlying fouling and antifouling mechanisms are characterized through direct molecular and surface force measurements. It is found that the commercial antifoulant exhibits exceptional antifouling performance at the dosage range of 20–35 ppm, and increasing stirring rate enhances the antifouling behavior. The force measurement results indicate that the antifoulant can adsorb to organics and target substrate surfaces, performing the antifouling function by lowering the hydrophobic interaction between organics and target substrates. This work provides a novel and feasible method for characterizing fouling phenomena and evaluating antifoulants under HTHP conditions and improves the understanding of fundamental interaction mechanisms underlying the fouling and antifouling phenomena.

Convection beyond the Steam Chamber Interface in the Steam-Assisted-Gravity-Drainage Process.

In the steam-assisted-gravity-drainage (SAGD) process, heat energy is transferred from the steam chamber to the farther cold reservoir by conduction and convection mechanisms, so as to reduce the oil viscosity. In previous research works, although it was proved that convection is an indispensable part of the heat-transfer process, there is still a controversy about the formation mechanism of heat convection. In this study, an analytical mathematic model was proposed to explore the convective heat transfer in SAGD operation. Typically, this model integrates three heat convection forms that are generated by pressure difference, gravity, and thermal expansion of connate water,. Subsequently, the simulation results are compared with field data to evaluate the accuracy of the new model, and they are reasonably consistent with UTF field data. The results indicate that convective heat transfer plays a predominant role in the immediate vicinity of the steam chamber interface. Furthermore, this paper derives a mathematic model of oil production to explore the effect of heat convection on oil production under different operation conditions. The results demonstrate that heat convection has an adverse impact on oil production, but it is inevitable. This study also displays that some parameters, such as the lateral spreading rate, the thermal diffusivity, the viscosity coefficient, and the curvature of oil relative permeability curve, can significantly affect the oil production rate. Based on this study, the effect of convection mechanism on the heat-transfer process and oil production will be further clarified, and the parameters in the SAGD process can be optimized, so as to effectively enhance and predict oil production.

An Improved Set of Design Criteria for Slotted Liners in Steam Assisted Gravity Drainage Operation

Slotted liners are widely used in steam-assisted gravity drainage (SAGD) wells to control sand production and sustain wellbore productivity. The slotted liner can provide desirable performance when appropriately designed. A literature review indicates a limited number of studies that offer design criteria specifically for SAGD wells. Moreover, past criteria seem to neglect some key factors, which may lead to inadequate slot design. This paper proposes a set of graphical design criteria for slotted liners in SAGD production wells, using prepacked sand retention testing (SRT) data. The SRT is designed to incorporate several essential factors that are not present in the past design criteria, such as slot density, steam breakthrough, and particle size distribution (PSD). The proposed design criteria are presented graphically for normal and aggressive conditions, where the aggressive condition accounts for the potential occurrence of the steam breakthrough. It is found that the upper bound of the design window is substantially lower for the aggressive condition due to the higher sand production after the steam breakthrough. The design criteria also indicate that the slotted liner is suitable only for the formations with low fines content.

Effect of Charge Density of Reverse Emulsion Breaker on Demulsification Performance for Steam-Assisted Gravity Drainage (SAGD) Emulsions under High Temperature and High Pressure

Reverse emulsion breakers (REBs) play a crucial role in the demulsification of complex water-in-oil-in-water (W/O/W) emulsions in steam-assisted gravity drainage (SAGD) production of oil sands. Developing effective REBs remains challenging due to the poor understanding of influencing factors and demulsification mechanisms. In particular, despite the recognition of the vital role of charge density of the REBs in their demulsification performance, the available literature is limited. Herein, we investigated the correlation between the charge density of commercial REBs and their demulsification performance for complex emulsions under simulated SAGD operation conditions (100–200 °C and 0.3–1.4 MPa) by employing an in-house-built bottle test system. It is demonstrated that a high charge density of the REBs not only promotes the qualities of produced water and oil but also significantly accelerates the speed of oil/water phase separation. At the microscale, the REB with a high charge density is capable of reducing the amount and size of residual oil droplets in produced water. The interactions of the species involved during the demulsification process were investigated by employing multiple techniques including optical microscopy imaging, ζ potential measurement, and dynamic light scattering. The results suggest that the cationic REBs are adsorbed at the oil/water interface, neutralize negative surface charge of oil droplets, and replace interface-active species originally present at the oil/water interface. Multilayer adsorption of REBs may be generated after demulsification, and the adsorbed REBs could partially desorb from the surface of oil droplets with increasing temperature. This work has delineated the influence of the charge density of REBs on their demulsification performance and improved the fundamental understanding of the interactions of the constituent species in SAGD emulsions and REBs, which provides useful information on the development and applications of efficient and cost-effective chemicals in oil sands exploitation and emulsion treatment.

A Numerical Model for Investigating the Steam Conformance along the Dual-String Horizontal Wells in SAGD Operations

Non-uniformity of the steam-assisted gravity drainage (SAGD) steam chamber significantly decreases the development of heavy oil reservoirs. In this study, to investigate the steam conformance in SAGD operations, a wellbore model is developed for fluid flow in dual-string horizontal wells. Then, a three-dimensional, three-phase reservoir model is presented. Next, the coupled wellbore and reservoir model is solved with a fully implicit finite difference method. Finally, the effects of the injector wellbore configuration, steam injection ratio and injection time on the steam conformance are investigated. The results indicate that under different injector wellbore configurations, the closer the differences between the pressure drop from the landing position of the short string to the heel of the wellbore and the pressure drop from the landing position of the short string to the toe of the wellbore, the better is the steam conformance. The smaller the difference in the steam injection rate between the long and short injection strings, the higher is the uniformity of the steam chamber. The injector annular pressure profile uniformity is consistent with the steam conformance. Creating a more uniform steam pressure in the annulus of the injector improves the uniformity of the steam chamber. The steam conformance decreases with increasing injection time, so the optimization method of steam chamber uniformity should be adjusted according to different injection times.