Improving Steam-Assisted Gravity Drainage Using Mobility Control Foams: Foam Assisted-SAGD (FA-SAGD)
- Qing Chen | Margot Geertrui Gerritsen (Stanford University) | Anthony Robert Kovscek (Stanford University)
- Document ID
- Society of Petroleum Engineers
- SPE Improved Oil Recovery Symposium, 24-28 April, Tulsa, Oklahoma, USA
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 5.3.9 Steam Assisted Gravity Drainage, 5.1.1 Exploration, Development, Structural Geology, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.2.1 Phase Behavior and PVT Measurements, 5.4.10 Microbial Methods, 5.3.1 Flow in Porous Media, 5.6.9 Production Forecasting, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.10 Drilling Equipment, 5.5 Reservoir Simulation, 5.7.2 Recovery Factors, 2.4.3 Sand/Solids Control, 5.1 Reservoir Characterisation, 5.4.6 Thermal Methods, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.2 Reservoir Fluid Dynamics, 1.6 Drilling Operations
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Steam-assisted gravity drainage (SAGD) is a promising approach for recovering heavy and viscous oil. The success of SAGD relies on two key operations: uniform formation of the steam chamber along the full length of the injector, and effective control of steam breakthrough by sustaining a liquid level between the injector and producer (i.e. a steam trap). Intrinsic permeability heterogeneities typically lead to a partially-developed steam chamber and potentially low sweep efficiency that results in reduced oil production. The injectivity variability along the well also complicates the control of steam breakthrough. To overcome these difficulties, we propose the use of foamed steam. The feasibility of foam-assisted SAGD (FA-SAGD) is demonstrated numerically with a local-equilibrium foam simulator incorporating the physical mechanisms of foam generation, destruction, and transport. The model was validated previously. Simulation results show that strong foam is generated and accumulates in the interwell region. The presence of foamed steam helps to control steam breakthrough and yields better recovery performance per barrel of steam injected than conventional SAGD. Live steam production in simulations is reduced by a factor of 5. Consequently, cumulative oil production is increased by about 30% in comparison to cases without foam. Sensitivity analysis of the parameters describing foam indicate that the process is robust.
Vast quantities of heavy and extra-heavy oil (bitumen) resources have been found worldwide. For example, an estimated original heavy oil in place of more than 1.8 trillion barrels is present in Venezuela, 1.7 trillion barrels in Alberta, Canada, and 20-25 billion barrels on the North Slope of Alaska, USA (Burton et al., 2005). Due to large crude oil viscosity, the efficient and economic recovery of these heavy-oil and bitumen resources presents a significant challenge. At reservoir conditions, heavy oil normally has viscosity much greater than 100 cp, and bitumen exhibits even greater viscosity. With such large viscosity, crude oil flows extremely slowly, if at all, at initial formation temperatures. Thus, the recovery of the unconventional heavy oil requires efficient in-situ viscosity reduction.
Thermal methods have been developed extensively over the past several decades for heavy-oil recovery. To date, more than 4 billion bbl of oil have been recovered in the USA alone as a result of steam injection (Moritis 2002). The essential idea of thermal recovery is to heat reservoir fluids thereby reducing oil viscosity according to the strong temperature dependency of oil viscosity (Bradley, 1987). Conventional thermal methods include cyclic steam injection, steam flooding, and in-situ combustion. To some extent, these methods all use gravity gravity drainage to recover oil (e.g. Aziz and Gontijo, 1984; Closmann, 1995). With recent advances in drilling horizontal wells and the understanding of the importance of gravity drainage to heavy-oil recovery, so-called steam-assisted gravity drainage (SAGD) has emerged as a promising heavy-oil recovery technique, especially for bitumen in Western Canada (Butler, 2001).
The concept of SAGD, initially proposed by Butler and his colleagues (Butler et al.,1981; Butler and Stephens, 1981), places two horizontal wells close to the bottom of a formation. The injection well is above the producer a short vertical distance (4-10 m). Steam is injected continuously into the upper well, and rises in the formation, forming a steam chamber. Cold oil surrounding the steam chamber is heated by thermal conduction and by mixing with warm oil. As oil temperature increases, it becomes mobile and flows together with condensate toward the producer (Butler, 1998b). The SAGD technique enjoys advantages over other thermal methods including shortcomings of steam override by employing only gravity as the driving mechanism. This leads to a more stable displacement, good drainage efficiency, and a high oil recovery. SAGD also benefits from the substantial contact of the horizontal well with the formation. Moreover, in the SAGD process, the heated oil remains hot and movable as it flows toward the production well.
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