On the Stability of the Edge of a Steam-Assisted-Gravity-Drainage Steam Chamber

SPE Journal ◽  
2013 ◽  
Vol 19 (02) ◽  
pp. 280-288 ◽  
Author(s):  
Mazda Irani ◽  
Ian Gates
Keyword(s):  
Heat Transfer ◽  
Diffusion Equation ◽  
Thermal Recovery ◽  
Gravity Drainage ◽  
Oil Sand ◽  
Steam Chamber ◽  
Steam Condensate ◽  
Steam Assisted Gravity Drainage ◽  
Pressure Diffusion ◽  
The Stability

Summary Steam-assisted gravity drainage (SAGD) is a successful thermal-recovery technique applied in oil-sand reservoirs in which the viscosity of the oil (bitumen) is typically in the hundreds of thousands to millions of centipoise. For the in-situ production from bitumen reservoirs, bitumen viscosity must be reduced to achieve the mobility required to flow toward the production well. Many factors influence the efficiency and rate at which bitumen is mobilized. The controlling feature of steam-based recovery processes is heat transfer from the steam chamber to the formation—the greater the heat flux, the larger the oil volume heated, and the higher the oil-drainage rate. Previous studies have demonstrated that instability at the steam-chamber edge can enhance heat transfer there by creating limited-amplitude steam fingers that enlarge the heat-transfer area, thus leading to greater thermal efficiency of the recovery process. This, in turn, increases oil production. At this point, stability studies have focused on the instability between steam and oil at the edge of the chamber—none has examined the case between steam condensate and oil. In the research documented here, the stability between steam condensate and bitumen at the edge of the chamber is explored. Here, a steam-pressure diffusion equation at the moving chamber interface is derived. The perturbations of the pressure and condensate velocity are substituted into the pressure diffusion equation and Darcy's law to realize a linear-stability equation governing the growth of disturbances at the interface. The results show that the stability is controlled by moving-interface velocity and reservoir water-phase hydraulic diffusivity.

Convection at the Edge of a Steam-Assisted-Gravity-Drainage Steam Chamber

SPE Journal ◽  
2011 ◽  
Vol 16 (03) ◽  
pp. 503-512 ◽  
Author(s):  
Jyotsna Sharma ◽  
Ian D. Gates
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Relative Permeability ◽  
Convective Heat ◽  
Injection Well ◽  
Gravity Drainage ◽  
Oil Sand ◽  
Production Well ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage

Summary Steam-assisted gravity drainage (SAGD) has become the preferred process to recover bitumen from Athabasca deposits in Alberta. The method consists of a lower horizontal production well, typically located approximately 2 m above the base of the oil zone, and an upper horizontal injection well located roughly 5 to 10 m above the production well. Steam flows from the injection well into a steam chamber that surrounds the wells and releases its latent heat to the cool oil sands at the edge of the chamber. This research re-examines heat transfer at the edge of the steam chamber. Specifically, a new theory is derived to account for convection of warm condensate into the oil sand at the edge of the chamber. The results show that, if the injection pressure is higher than the initial reservoir pressure, convective heat transfer can be larger than conductive heat transfer into the oil sand at the edge of the chamber. However, enhancement of the heat-transfer rate by convection may not necessarily imply higher oil rates; this can be explained by relative permeability effects at the chamber edge. As the condensate invades the oil sand, the oil saturation drops and, consequently, the oil relative permeability falls. This, in turn, results in the reduction of the oil mobility, despite the lowered oil viscosity because of higher temperature arising from convective heat transfer.

Understanding the Convection Heat-Transfer Mechanism in the Steam-Assisted-Gravity-Drainage Process

SPE Journal ◽  
2013 ◽  
Vol 18 (06) ◽  
pp. 1202-1216 ◽  
Author(s):  
Mazda Irani ◽  
Ian Gates
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat ◽  
Gravity Drainage ◽  
Heat Transfer Mechanism ◽  
Oil Sand ◽  
Convective Flux ◽  
Convective Heat Flux ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage

Summary Steam-assisted gravity drainage (SAGD) is the preferred method to extract bitumen from Athabasca oil-sand reservoirs in western Canada. In SAGD, steam, injected outward from a horizontal injection well, loses its latent heat when it contacts the cold bitumen at the edge of a steam chamber. Consequently, the viscosity of the bitumen falls several orders of magnitude, enabling it to flow under gravity toward a horizontal production well directly below to the injection well. It is commonly believed that conduction is the dominant heat-transfer mechanism at the edge of the chamber. Heat transfer by convection is not considered in classic SAGD mathematical models such as the one derived by Butler. Researchers such as Butler and Stephens (1981), Reis (1992), Akin (2005), Liang (2005), Nukhaev et al. (2006), and Azad and Chalaturnyk (2010) considered the conduction from steam to cold reservoir to be the only heat-transfer component. Farouq-Ali (1997), Edmunds (1999a, b), Ito and Suzuki (1996, 1999), Ito et al. (1998), Sharma and Gates (2011), and Irani and Ghannadi (2013) questioned the assumption that thermal conduction dominates heat transfer at the edge of a SAGD chamber. Sharma and Gates (2011) and Irani and Ghannadi (2013) studied convective flux from condensate flow at the edge of an SAGD steam chamber. Irani and Ghannadi (2013) derived a new formulation that solves the energy balance and pressure-driven condensate flow normal to the steam-chamber interface into the cold bitumen reservoir and concluded that the assumption of conduction-dominated heat transfer is valid; however, all previous analyses do not include convective heat transfer arising from draining bitumen and condensate. Although a few researchers have studied convective flux from condensate flow at the edge of an SAGD steam chamber (e.g., Sharma and Gates 2011; Irani and Ghannadi 2013), there is a lack of understanding of bitumen and condensate drainage parallel to the edge of the chamber and of its effect on transverse heat transfer into the oil sand beyond the chamber. In this study, the relative roles of convective heat flux both parallel and normal to the edge of a steam chamber are examined. The results suggest that the convective heat flux associated with flow parallel to the chamber edge is minor compared with that normal to the edge.

Approximate Physics-Discrete Simulation of the Steam-Chamber Evolution in Steam-Assisted Gravity Drainage

SPE Journal ◽  
2018 ◽  
Vol 24 (02) ◽  
pp. 477-491 ◽  
Author(s):  
Enrique Gallardo ◽  
Clayton V. Deutsch
Keyword(s):  
Oil Sands ◽  
Recovery Process ◽  
Thermal Recovery ◽  
Porous Media Flow ◽  
Gravity Drainage ◽  
Discrete Simulation ◽  
Flow Equations ◽  
Integrity Assessment ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage

Summary Steam-assisted gravity drainage (SAGD) is a thermal-recovery process to produce bitumen from oil sands. In this technology, steam injected in the reservoir creates a constantly evolving steam chamber while heated bitumen drains to a production well. Understanding the geometry and the rate of growth of the steam chamber is necessary to manage an economically successful SAGD project. This work introduces an approximate physics-discrete simulator (APDS) to model the steam-chamber evolution. The algorithm is formulated and implemented using graph theory, simplified porous-media flow equations, heat-transfer concepts, and ideas from discrete simulation. The APDS predicts the steam-chamber evolution in heterogeneous reservoirs and is computationally efficient enough to be applied over multiple geostatistical realizations to support decisions in the presence of geological uncertainty. The APDS is expected to be useful for selecting well-pair locations and operational strategies, 4D-seismic integration in SAGD-reservoir characterization, and caprock-integrity assessment.

Understanding the Thermo-Hydromechanical Pressurization in Two-Phase (Steam/Water) Flow and Its Application in Low-Permeability Caprock Formations in Steam-Assisted-Gravity-Drainage Projects

SPE Journal ◽  
2014 ◽  
Vol 19 (06) ◽  
pp. 1126-1150 ◽  
Author(s):  
Sahar Ghannadi ◽  
Mazda Irani ◽  
Rick Chalaturnyk
Keyword(s):  
Pore Pressure ◽  
Shear Failure ◽  
Thermal Recovery ◽  
Subcritical State ◽  
Gravity Drainage ◽  
Low Permeability ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage ◽  
Caprock Integrity ◽  
Casing Failure

Summary Steam-assisted gravity drainage (SAGD) is one successful thermal-recovery technique applied in Alberta oil-sand reservoirs. When considering in-situ production from bitumen reservoirs, one must reduce viscosity for the bitumen to flow toward the production well. Steam injection is currently the most promising thermal-recovery method. Although steamflooding has proved to be a commercially viable way to extract bitumen from bitumen reservoirs, caprock integrity and the risk of losing steam containment can be challenging operational problems. Because permeability is low in Albertan thermal-project caprock formations, heating greatly increases the pressure on any water trapped in pores as a result of water thermal expansion. This water also sees a great increase in volume as it flashes to steam, causing a large effective-stress reduction. After this condition is established, pore-pressure increases can lead to caprock shear failure or tensile fracturing, and to subsequent caprock-integrity failure or potential casing failure. It is typically believed that low-permeability caprocks impede the transmission of pore pressure from reservoirs, making them more resistant to shear failure (Collins 2005, 2007). In considering the “thermo-hydromechanical pressurization” physics, low-permeability caprocks are not always more resistant. As the steam chamber rises into the caprock, the heated pore fluids may flash to steam. Consequently, there is a vapor region between the steam-chamber interface penetrated into the caprock and the water region within the caprock which is still at a subcritical state. This study develops equations for fluid-mass and thermal-energy conservation, evaluating the thermo-hydromechanical pressurization in low-permeability caprocks and the flow of steam and water after steam starts to be injected as part of the SAGD process. Calculations are made for both short-term and long-term responses, and evaluated thermal pressurization is compared for caprocks with different stiffness states and with different permeabilities. One can conclude that the stiffer and less permeable the caprock, the greater the thermo-hydromechanical pressurization; and that the application of SAGD can lead to high pore pressure and potentially to caprock shear, and to subsequent steam release to the surface or potential casing failure.

scholarly journals Expansion Velocity Model of Steam-Assisted Gravity Drainage considering Thermal Convection

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Dian-Fa Du ◽  
Yao-Zu Zhang ◽  
Li-Na Zhang ◽  
Meng-Ran Xu ◽  
Xin Liu
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Heavy Oil ◽  
Heat Convection ◽  
Gravity Drainage ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage ◽  
Expansion Speed ◽  
Actual Field ◽  
Horizontal Expansion

Steam-assisted gravity drainage (SAGD) is an important method used in the development of heavy oil. A heat transfer model in the SAGD production process is established based on the heat transfer effect caused by the temperature difference at the front edge of the steam chamber and the heat convection effect caused by the pressure difference. The observation well temperature method is used in this model to calculate the horizontal expansion speed of the steam chamber. In this manner, an expansion speed model considering heat convection and heat conduction is established for a steam chamber with a steam-assisted gravity drainage system. By comparing this with the production data extracted from the Fengcheng Oilfield target block, it is verified that the model can be effectively applied for actual field development. Simultaneously, by using the derived model, the temperature distribution at the edge of the steam chamber and production forecast can be predicted. Sensitivity analysis of the expansion rate of the steam chamber demonstrates that the larger the thermal conductivity, the faster is the steam chamber horizontal expansion speed, and the two are positively correlated; the larger the reservoir heat capacity, the slower is the steam chamber horizontal expansion speed. A larger heat capacity of the convective liquid indicates that there are more water components in the convective liquid, the viscosity of the convective liquid is low, and the expansion speed of the steam chamber increases accordingly. This research closely integrates theory with actual field production and provides theoretical support for the development of heavy oil reservoirs.

A New Mathematical Model to Understand the Convective Heat Transfer Mechanism in Steam-Assisted Gravity Drainage Process

2017 ◽  
Vol 10 (1) ◽  
Author(s):  
Zhaoxiang Zhang ◽  
Huiqing Liu ◽  
Xiaohu Dong ◽  
Huanli Jiang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Analytical Model ◽  
Convective Heat ◽  
Transfer Mechanism ◽  
Gravity Drainage ◽  
Heat Transfer Mechanism ◽  
Oil Viscosity ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage

Steam-assisted gravity drainage (SAGD) process has been an optimized method to explore heavy oil reservoirs in the world. The oil viscosity reduction and gravity force near the interface of steam–chamber are the main development mechanisms. In classical models, conductive heat transfer plays the only or dominant role in the heat transmission from high-temperature steam to low-temperature oil sands. Although some mathematical studies have paid attention to the convective heat transfer, the role of heat transfer by flowable oil normal to the steam–chamber interface has been given little attention. In SAGD, the viscosity of bitumen can be reduced by several orders of magnitude by the release of latent heat from injected steam. In this study, an analytical model is developed for the heat transfer process induced by flowable oil. Also, in order to accurately simulate the oil viscosity characteristics in steam–chamber, a correlation between oil viscosity and pressure is proposed. Results indicate that the oil mobility plays an important role on the flow normal to interface when the distance is smaller than 6 m. Even under the most extreme circumstances (μw = 0.1127 cp), the flowing of oil normal to steam–chamber interface also cannot be ignored. Comparing to Irani and Ghannadi model, it can be easy to draw the conclusion that the new model consists with the underground test facility (UTF) field data much better. This new analytical model will benefit to understanding the convective heat transfer mechanism in SAGD process.

scholarly journals Monitoring of steam chamber in steam-assisted gravity drainage based on the temperature sensitivity of oil sand

2021 ◽  
Vol 48 (6) ◽  
pp. 1411-1419
Author(s):  
Yunfeng GAO ◽  
Ting'en FAN ◽  
Jinghuai GAO ◽  
Hui LI ◽  
Hongchao DONG ◽  
...  
Keyword(s):  
Temperature Sensitivity ◽  
Gravity Drainage ◽  
Oil Sand ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage

Discussion on the Effects of Temperature on Thermal Properties in the Steam-Assisted-Gravity-Drainage (SAGD) Process. Part 1: Thermal Conductivity

SPE Journal ◽  
2013 ◽  
Vol 21 (02) ◽  
pp. 334-352 ◽  
Author(s):  
Mazda Irani ◽  
Marya Cokar
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Temperature Profile ◽  
Conductive Heat Transfer ◽  
Gravity Drainage ◽  
Conductive Heat ◽  
Temperature Dependent ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage ◽  
Temperature Dependent Thermal Conductivity

Summary Steam-assisted gravity drainage (SAGD) is the preferred thermal-recovery method used to produce bitumen from Athabasca deposits in Alberta, Canada. In SAGD, steam injected into a horizontal injection well is forced into the reservoir, losing its latent heat when it comes into contact with cold bitumen at the edge of a depletion chamber. Heat energy is transferred from steam to reservoir, resulting in reduced bitumen viscosity that enables the bitumen to flow toward the horizontal production well under gravity forces. Conduction is the main heat-transfer mechanism at the edge of the steam chamber in SAGD, and reservoir thermal conductivity is a key parameter in conductive-heat transfer. Conductive-heat transfer occurs at higher rates across reservoirs with higher thermal conductivity, which in turn affects the temperature profile ahead of the steam interface. Consequently, a reservoir with higher thermal conductivity will result in higher reservoir-heating rates, which lead to higher oil rates. However, when oil-sand reservoirs are heated from reservoir temperature to steam-chamber temperature, the thermal conductivity can decrease up to 25%, which affects the temperature profile and conductive heating at the edge of the steam-saturated zone known as the steam chamber. This study provides an analytical model that includes a temperature-dependent thermal-conductivity value. This novel approach is the first of its kind to incorporate a temperature-dependent thermal-conductivity value within an analytical SAGD model to predict temperature front, oil production, and steam/oil ratio (SOR). Furthermore, if Butler's (1985) model is used, the results reveal that the arithmetic average thermal-conductivity values at reservoir and steam temperatures could be used for temperature-profile prediction, which would result in an error of less than 1% for the range of SAGD applications. The results of this study suggest that the minimum error for oil rates depends on the viscosity/temperature correlation. The optimum thermal conductivity should be calculated at the temperature that gives dimensionless temperatures [i.e., (T−Tr)/(Tst−Tr)] varying between 0.75 to 0.85 for m-values [Butler-suggested power constants (Butler 1985, 1991; Butler and Stephens 1981)] between 3 and 5.6. This study also investigates the effect of including temperature-dependent thermal conductivity on SOR variation and suggests that for both laterally expanding and angularly expanding reservoirs the SOR is independent of the thermal conductivity.

Predicting Geomechanical Dynamics of Steam-Assisted Gravity-Drainage Process. Part II: Modified Cam-Clay Model

SPE Journal ◽  
2020 ◽  
Vol 25 (06) ◽  
pp. 3366-3385
Author(s):  
Mazda Irani
Keyword(s):  
Monitoring Program ◽  
Test Facility ◽  
Elastic Behavior ◽  
Gravity Drainage ◽  
Oil Sand ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage ◽  
Heated Zone ◽  
Modified Cam Clay ◽  
Cam Clay

Summary In Part I of this study (Irani 2018), the geomechanical effects in the reservoir associated with steam-assisted gravity drainage (SAGD) steam chamber growth was evaluated on the basis of two core assumptions: reservoir yield behavior follows that of the Mohr-Coulomb (MC) dilative behavior, and the reservoir stress response follows that of a drained sand. In Part I, it was shown that although the dilative model nicely described the shearing and the sheared zone thickness at the front of the SAGD steam chamber, it could not predict the displacements associated with cold dilation in SAGD reservoirs, in which cold dilation refers to vertical displacement created in the zone ahead of the heated zone caused by isotropic unloading generated by the pore pressure increase and the increase in far-field horizontal stress. In cold dilation, the stresses do not reach the critical state line (CSL), which defines the yield surface and should, therefore, be analyzed considering elastic behavior. A modified Cam-Clay (MCC) model, however, can be used to describe the behavior of the oil sand in the cold dilation zone before reaching the CSL. In this study and as an extension to the results presented in Part I, strains developed in the reservoir during SAGD operation are calculated using an MCC model, and the associated oil rate enhancement and displacements are evaluated. The vertical strains and displacements are compared with measured values from the extensive monitoring program conducted at the Underground Test Facility (UTF) in the late 1980s. Two aspects of geomechanical effects are compared between the cap models (Part II) and dilative models (Part I): first, prediction of the sheared zone thickness and its effect on SAGD production enhancement, and second, prediction of vertical and horizontal displacements. It is shown that consideration of the material model effects on production rates are negligible for both models and that the MCC model can predict displacements in both the heated and cold zones of the reservoir reasonably accurately. Although dilative constitutive models can be used to predict horizontal and vertical displacements in the heated zone quite accurately, they lack the ability to predict the response in the “cold dilation zone.” Another main advantage of using an MCC model is that the MCC model provides a better description of a stress path and how the reservoir mobility can affect reservoir dilation, especially in the cold dilation zone.

A New Approach to the Analytical Treatment of Steam-Assisted Gravity Drainage: A Prescribed Interface Model

SPE Journal ◽  
2019 ◽  
Vol 24 (02) ◽  
pp. 492-510 ◽  
Author(s):  
Mohsen Keshavarz ◽  
Thomas G. Harding ◽  
Zhangxin Chen
Keyword(s):  
Heat Transfer ◽  
Production Rate ◽  
Material Balance ◽  
Oil Production ◽  
Gravity Drainage ◽  
Conductive Heat ◽  
Analytical Treatment ◽  
New Approach ◽  
Steam Chamber ◽  
Steam Assisted Gravity Drainage

Summary The majority of the models in the literature for the steam-assisted-gravity-drainage (SAGD) process solve the problem of conductive heat transfer ahead of a moving hot interface using a quasisteady-state assumption and extend the solution to the base of the steam chamber where the interface is not moving. This approach, as discussed by Butler (1985) and Reis (1992), results in inaccurate or sometimes infeasible estimations of the oil-production rate, steam/oil ratio (SOR), and steam-chamber shape. In this work, a new approach for the analytical treatment of SAGD is proposed in which the problem of heat transfer is directly solved for a stationary source of heat at the base of the steam chamber, where the oil production occurs. The distribution of heat along the interface is then estimated depending on the geometry of the steam chamber. This methodology is more representative of the heat-transfer characteristics of SAGD and resolves the challenges of those earlier models. In addition, it allows for the extension of the formulations to the early stages of the process when the side interfaces of the chamber are almost stationary, without loss of the solution continuity. The model requires the overall shape of the steam chamber as an input. It then estimates the movement of chamber interfaces using the movement of the uppermost interface point and by satisfying the global material-balance requirements. Oil-production rate and steam demand are estimated by Darcy's law and energy-balance calculations, respectively. The result is a model that is applicable to the entire lifetime of a typical SAGD project and provides more-representative estimations of in-situ heat distribution, bitumen-production rate, and SOR. With the improved knowledge obtained on the fundamentals of heat transfer in SAGD, the reason for the discrepancies between the various earlier models will be clarified. Results of the analytical models developed in this work show reasonable agreement with fine-scale numerical simulation, which indicates that the primary physics are properly captured. In the final section of the paper, the application of the developed models to two field case studies will be demonstrated.

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