90 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
injected through the upper well, creates a steam chamber along
the walls of which the heated bitumen flows and is produced in
the lower well.
Several variations of this process have been developed. One variation uses a single horizontal well, with steam injection through a
central pipe and production along the annulus. Another variation
involves steam injection through existing vertical wells and production through an underlying horizontal well. The key benefits of
the SAGD process are an improved steam-oil ratio and high ultimate recovery (on the order of 60 to 70%). The outstanding technical issues relate to low initial oil rate, artificial lifting of bitumen
to the surface, horizontal well operation and the extrapolation of
the process to reservoirs having low permeability, low pressure or
bottom water.
Heat generation is a major economic constraint on all thermal
processes. Currently, steam is generated with natural gas, and
when the cost of natural gas rises, operating costs rise considerably.
Thermally, SAGD is about twice as efficient as cyclic steam stimulation, with steam-oil ratios that are now approaching two (instead
of four for cyclic steam soak), for similar cases. Combined with the
high recovery ratios possible, SAGD will likely displace pressuredriven thermal process in all cases where the reservoir is reasonably thick.
Vapor-assisted petroleum extraction (VAPEX) is a new process
in which the physics of the process are essentially the same as for
SAGD and the configuration of wells is generally similar. The process involves the injection of vaporized solvents such as ethane or
propane to create a vapor-chamber through which the oil flows due
to gravity drainage (Butler and Mokrys, 1991; United States Patent
5,407,009; United States Patent 5,607,016. 1995; Butler and Jiang,
2000). The process can be applied in paired horizontal wells, single
horizontal wells or a combination of vertical and horizontal wells.
The key benefits are significantly lower energy costs, potential for
in situ upgrading and application to thin reservoirs, with bottom
water or reactive mineralogy.
VAPEX can be used in conjunction with SAGD methods. A key
factor is the generation of a three-phase system with a continuous
gas phase so that as much of the oil as possible can be contacted
by the gaseous phases, generating the thin oil film drainage mechanism. Vertical permeability barriers are a problem, and must be
overcome through hydraulic fracturing to create vertical permeable
injected through the upper well, creates a steam chamber along
the walls of which the heated bitumen flows and is produced in
the lower well.
Several variations of this process have been developed. One variation uses a single horizontal well, with steam injection through a
central pipe and production along the annulus. Another variation
involves steam injection through existing vertical wells and production through an underlying horizontal well. The key benefits of
the SAGD process are an improved steam-oil ratio and high ultimate recovery (on the order of 60 to 70%). The outstanding technical issues relate to low initial oil rate, artificial lifting of bitumen
to the surface, horizontal well operation and the extrapolation of
the process to reservoirs having low permeability, low pressure or
bottom water.
Heat generation is a major economic constraint on all thermal
processes. Currently, steam is generated with natural gas, and
when the cost of natural gas rises, operating costs rise considerably.
Thermally, SAGD is about twice as efficient as cyclic steam stimulation, with steam-oil ratios that are now approaching two (instead
of four for cyclic steam soak), for similar cases. Combined with the
high recovery ratios possible, SAGD will likely displace pressuredriven thermal process in all cases where the reservoir is reasonably thick.
Vapor-assisted petroleum extraction (VAPEX) is a new process
in which the physics of the process are essentially the same as for
SAGD and the configuration of wells is generally similar. The process involves the injection of vaporized solvents such as ethane or
propane to create a vapor-chamber through which the oil flows due
to gravity drainage (Butler and Mokrys, 1991; United States Patent
5,407,009; United States Patent 5,607,016. 1995; Butler and Jiang,
2000). The process can be applied in paired horizontal wells, single
horizontal wells or a combination of vertical and horizontal wells.
The key benefits are significantly lower energy costs, potential for
in situ upgrading and application to thin reservoirs, with bottom
water or reactive mineralogy.
VAPEX can be used in conjunction with SAGD methods. A key
factor is the generation of a three-phase system with a continuous
gas phase so that as much of the oil as possible can be contacted
by the gaseous phases, generating the thin oil film drainage mechanism. Vertical permeability barriers are a problem, and must be
overcome through hydraulic fracturing to create vertical permeable