Analytical Treatment of Steam-Assisted Gravity Drainage: Old and New
- Zeinab Zargar (University of Calgary) | S. M. Farouq Ali (University of Calgary)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- February 2018
- Document Type
- Journal Paper
- 117 - 127
- 2018.Society of Petroleum Engineers
- Analytical Modelling, SAGD, Moving boundary problem, Sideways expansion, Rise velocity
- 1 in the last 30 days
- 392 since 2007
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Steam-assisted gravity drainage (SAGD) is a widely tested method for producing bitumen from oil sands (tar sands). Several analytical treatments of the basic process have been reported. In a typical model, the focus is on bitumen drainage ahead of an advancing heat front. In a few cases, a steady expression for bitumen-drainage rate is obtained. This has been modified by several investigators to include other effects. In all cases, the bitumen rate is obtained with no recourse to the steam-injection rate, which is worked out after the fact. The treatment of time dependence, in a few models, is tenuous, building it in partly by use of experimental data.
In this work, the SAGD process is considered to develop during two stages: steam-chamber rise (or unsteady stage) and sideways-expansion (or steady stage). The sideways-expansion phase is modeled by two different approaches: constant volumetric displacement (CVD) and constant heat injection (CHI).
In the transient-steam-chamber-rise stage of SAGD, initially there is no heat ahead of the rising front, but as the front rises with time, heat accumulates ahead of the front. In the sideways-spreading stage, there is a dynamic equilibrium situation. The accumulated heat ahead of the front plays a crucial role in this phase of SAGD modeling to find the advancing-front velocity. There is a reciprocal relation between the advancing-front velocity and the amount of stored heat ahead of the front. Higher front velocity leads to lower heat accumulation ahead of the front for mobilizing oil ahead and making it drain. By considering the equilibrium situation for thermal-recovery methods with a dominant-gravity-drainage driving force, the advancing-front velocity is responsible for heat accumulation ahead of the front, and, in turn, this heated oil drains away and is responsible for advancing the front. Therefore, the key point in the modeling is to determine the advancing-front movement that satisfies heat and mass balances over the system under equilibrium.
In the CVD model, we postulate that the front movement is such that the steam-chamber growth is constant; that is, the oil-production rate is constant over time. In this work, it is shown that to obtain a constant oil-production rate from a mass balance, the injected heat has to be increased to compensate for the heat loss to the overburden and the growing accumulated heat ahead of the front caused by interface extension and decreasing front velocity.
In the CHI model, heat is injected at a constant rate into the system, which provides heat for the growing steam-chamber size, increasing heat loss to the overburden, and heat flow by conduction ahead of the front. In this model, we are computing the front velocity that satisfies heat balance and mass balance for a constant heat-injection rate. Decreasing steam-chamber velocity with time from this model leads to decreasing oil-production rate.
The modeling of the SAGD process in this work is different from that in previous works because it is believed that the steam-chamber velocity is the key point in SAGD modeling. In the CVD model, a constant maximum steam-chamber velocity is derived that gives a constant oil-production rate with a better agreement with field data. In the CHI approach, steam-chamber velocity, and hence the oil-production rate, is decreasing with time (strongly affected by increasing heat loss to the overburden).
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Azom, P. N., Kamp, A. M., and Srinivasan, S. 2013. Characterizing the Effect of Heat Transfer on Multiphase Flow during the Steam-Assisted Gravity Drainage (SAGD) Process. Presented at the SPE Heavy Oil Conference Canada, Calgary, 11–13 June. SPE-165494-MS. https://doi.org/10.2118/165494-MS.
Butler, R. M. 1985. A New Approach to the Modelling of Steam-Assisted Gravity Drainage. J Pet Can Technol 24 (3): 42–51. PETSOC-85-03-01. https://doi.org/10.2118/85-03-01.
Butler, R. M. 1987. Rise of Interfering Steam Chambers. J Can Pet Technol 26 (3): 70–75. PETSOC-87-03-07. https://doi.org/10.2118/87-03-07.
Butler, R. M. 1994. Horizontal Wells for the Recovery of Oil, Gas, and Bitumen. Calgary: Petroleum Society, Canadian Institute of Mining, Metallurgy and Petroleum.
Butler, R. M. 1997. Thermal Recovery of Oil and Bitumen. Calgary: Grav-Drain, Inc.
Butler, R. M. and Stephens, D. J. 1981. The Gravity Drainage of Steamheated Heavy Oil to Parallel Horizontal Wells. J Can Pet Technol 20 (2): 90–96. PETSOC-81-02-07. https://doi.org/10.2118/81-02-07.
Butler, R. M., McNab, G. S., and Lo, H. Y. 1981. Theoretical Studies on the Gravity Drainage of Heavy Oil during Steam Heating. Can. J. Chem. Eng. 59 (4): 455–460. https://doi.org/10.1002/cjce.5450590407.
Cenovus Energy. 2015. Cenovus Christina Lake In-situ Oil Sands Scheme 8591 Technical Report, Christina Lake Project. Calgary: Cenovus Energy.
Closmann, P. J. and Smith, R. A. 1983. Temperature Observations and Steam-Zone Rise in the Vicinity of a Steam-Heated Fracture. SPE J. 23 (4): 575–586. SPE-9898-PA. https://doi.org/10.2118/9898-PA.
Heidari, M., Pooladi-Darvish, M., Azaiez, J. et al. 2009. Effect of Drainage Height and Permeability on SAGD Performance. J. Pet. Sci. Eng. 68 (1–2): 99–106. https://doi.org/10.1016/j.petrol.2009.06.020.
Ito, Y., Suzuki, S., and Yamada, H. 1998. Effect of Reservoir Parameter on Oil Rates and Steam Oil Ratios in SAGD Projects. Oral presentation given at the 7th UNITAR International Conference on Heavy Crude and Tar Sands, Beijing, 27–30 October.
Murtaza, M. and Dehghanpour, H. 2012. Three-Phase Flow During Steam Chamber Presented at the SPE Improved Oil Recovery Symposium, Tulsa, 14–18 April. SPE-154287-MS. https://doi.org/10.2118/154287-MS.
Pooladi-Darvish, M., Tortike, W. S., and Farouq Ali, S. M. 1995. A New Semi-Analytical Model for Thermal Recovery Processes. Presented at the SPE Western Regional Meeting, Bakersfield, California, 8–10 March. SPE-29660-MS. https://doi.org/10.2118/29660-MS.
Reis, J. C. 1992. A Steam-Assisted Gravity Drainage Model for Tar Sands: Linear Geometry. J Can Pet Technol 31 (10): 14–20. PETSOC-92-10-01. https://doi.org/10.2118/92-10-01.
Sharma, J. and Gates, I. D. 2010. Multiphase Flow at the Edge of a Steam Chamber. Can. J. Chem. Eng. 88 (3): 312–324. https://doi.org/10.1002/cjce.20280.
Vogel, J. V. 1984. Simplified Heat Calculations for Steamfloods. J Pet Technol 36 (7): 1127–1136. SPE-11219-PA. https://doi.org/10.2118/11219-PA.