Coinjection of dimethyl ether and steam for bitumen and heavy-oil recovery

Physical Sciences : Petroleum

Available for licensing

Inventor

  • Ryosuke Okuno, Ph.D. , Petroleum and Geosystems Engineering

Background/unmet need

Steam injection is the most widely used method for in-situ recovery of bitumen and heavy oil. Important applications of steam injection include steam-assisted gravity drainage and cyclic steam stimulation. These conventional methods require a large amount of steam to increase the mobility of viscous oil in the reservoir. For example, a typical project of steam-only injection requires five barrels of water in the form of steam to recover one barrel of oil. It is important to improve the efficiency of steam-injection processes by reducing the steam requirement.

A potential way is to coinject solvent with steam, in which oil viscosity is reduced by dilution with the solvent condensed in situ and by the heat released from the injected steam. Hydrocarbon solvents have been studied as potential additives to steam for this purpose. The hydrocarbon solvents that are reported to be suitable have vapor pressures that are close to that of water. However, such hydrocarbon solvents are so expensive that in-situ retention of the coinjected solvent can substantially affect project economics. Less volatile solvents, such as propane and butane, are less expensive, but they are often too volatile for coinjection with steam. Coinjection of these highly-volatile solvents with steam has been reported to not be beneficial in many studies, and it can be even less profitable than the conventional steam-only injection.

Invention Description

This invention is concerned with dimethyl ether (DME) as a novel additive to steam for bitumen and heavy-oil recovery. DME is coinjected with steam into a viscous-oil reservoir in a similar way to steam-assisted gravity drainage and cyclic steam stimulation. DME and steam propagate in the reservoir in the form of vapor. They condense near thermal fronts, at which oil viscosity is reduced by the latent heat released and by the dilution of oil by the condensed DME.

Coinjection of a solvent with steam significantly reduces the amount of steam required for gravity drainage in comparison to traditional steam-assisted drainage. The reduced amount of steam does not hinder the rate of oil production. Improved efficiency of oil recovery by coinjection is significant to new oil fields in which conventional steam-only injection is ineffective for drainage.

Benefits/Advantages

  • Reduced amount of steam needed (e.g., 60%) compared to what is needed for steam-only injections, while maintaining the same rate of oil production
  • Reduced in-situ retention of DME
  • DME costs less than liquid hydrocarbon solvents, resulting in more opportunities to apply this technique to a wide variety of reservoir conditions 
  • DME recovery is less challenging than that of hydrocarbon solvents, because it can be recovered by the oleic and aqueous phases that flow into the producing well, while hydrocarbon solvents can be recovered only through the oleic phase

Features

  • The volatility of DME results in a lower operating temperature than steam-only injection, reducing the amount of heat lost to surroundings.
  • Though DME is similar to propane in terms of volatility, the operating temperature of DME is much higher due to solubility of DME in water, resulting in a lower steam requirement while keeping the same level of oil production.
  • Coinjection of DME with steam can be followed by steam-only injection to wash out the DME remaining in the reservoir.

Market potential/applications

There are approximately five trillion barrels of bitumen/heavy-oil resources in the world, approximately 50% of which are in Canada. Every one percent of incremental bitumen/heavy-oil recovery yields 50 billion barrels of oil production, equivalent to trillions of dollars in the marketplace.

The improved efficiency by this invention will increase the amount of bitumen/heavy-oil resources that can be economically recoverable. The reduced hurdle for development of new oil fields will result in additional job creation, improved energy security, and additional investments to various countries.

IP Status

  • 1 PCT patent application filed
  • 1 U.S. patent issued: 10,125,591