Method for high temperature steam

Abstract

A method for the recovery of upgraded oil from an oil-bearing formation is provided wherein a hot gas phase fluid comprising steam is brought into contact with a heavy oil reservoir, such as by injection, and the hot fluid heats at least a portion of the reservoir to a temperature high enough for steam cracking, and subsequently the steam is reacted with the heavy oil to produce steam cracked lighter oil.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. Provisional Application No. 60 / 606,755 filed Sep. 1, 2004, and U.S. Provisional Application No. 60 / 606,756 filed Sep. 1, 2004.BACKGROUND [0002] 1. Field of the Invention [0003] This invention provides a novel concept for the mobility enhancement of heavy crude oil, thus making possible more efficient and effective recovery of oils including oils that are presently accessible using existing techniques. Such oils include not only the balance of the oil left after primary and secondary recovery operations, but heavy oils and bitumen such as found in Athabaskan oil sands. More particularly, the present invention provides a downhole crude oil processing method that improves reservoir sweep efficiency and enhances quality of the crude oil delivered to the surface. In addition, coke formed may be recovered in the form of natural gas. Cost per barrel is consequently reduced. The method of the present i...

AI Technical Summary

Benefits of technology

[0010] In one embodiment of the present invention, steam from a conventional surface boiler is mixed with sufficient oxygen wherein the oxygen is combusted with carbon to form CO2. The fluid temperature would be high enough to heat the oil to a temperature sufficient to induce cracking of the oil. In this embodiment, all the heat of combustion released is delivered to the reservoir to enhance steam cracking. The steam and oxygen present react with carbon thus maintaining reservoir porosity. The optional injection of catalyst into the steam combustion product stream further promotes cracking of the heavy oil and allows control of pH.

[0013] Free hydrogen is produced from carbon even at temperatures as low as 700 degrees Fahrenheit. Thus, hydrogen is available for in situ desulfurization of reservoir oil. Both cracking and desulfurization lower oil viscosity thereby upgrading the oil. Sweep efficiency is improved via enhancement of mobility and control of reservoir permeability as a result of the reduction of intrinsic oil viscosity. Thus effective recovery of the oil in place can exceed ninety percent.

[0014] In another embodiment of the present invention, steam at a temperature high enough for steam cracking may be produced by downhole combustion of a fuel supplied from the surface together with water. The water is converted to steam of a desired temperature downhole thereby eliminating the need for a surface steam boiler. In this embodiment all combustion products are delivered downhole and boiler heat losses are avoided. Any known combustor system may be used.

[0015] Preferably, a catalytic combustion system is provided downhole. Catalytic combustors have two interrelated features that allow downhole combustion of hydrocarbon fuels for generation of a higher temperature steam: combustion stability and soot free operation. Operation within normal flame stability limits is not required allowing use of low BTU fuels. This approach retains all the benefits of downhole steam generation while adding the benefits of in-situ oil upgrading and thereby significantly reducing costs and improving sweep efficiency.

Problems solved by technology

However, it has been increasingly clear that production cannot keep up with the rapidly growing need, particularly in view of the growing demand from countries such as China and India.

Moreover, the bulk of new production must come from the politically unstable Middle East.

However, by far the bulk of such heavy oil reserves occur at depths greater than that from which it can be recovered by surfaces mining.

The oil removed tends to be the more mobile fraction of the reservoir, and the combustion emissions of the steam generator can be limiting (as in California).

Such steam flooding faces limiting technical and economic obstacles relating to conductive heat losses through the wellbore and incomplete reservoir sweep efficiency, especially in heterogeneous reservoirs.

With a large fraction of heavy oils there is a further problem: even if the heavy oil is heated sufficiently to promote flow to a wellhead, heat loss in flowing to the surface from typical reservoir depths will result in some loss of fluidity of the heavy oil before reaching the surface.

In addition, the oil produced cannot be transported by pipeline without dilution with a lighter oil.

Further, although surface mining can recover close to 100 percent of the oil in place, steam flooding typically can recover as little as fifty percent of the oil in place.

Capital costs are high and the availability of natural gas to produce the needed hydrogen can be an issue.

Unfortunately, fire flooding is difficult to control and the in-situ coking can plug the deposit.

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