Wells – Processes – Electric current or electrical wave energy through earth for...
Reexamination Certificate
2002-01-15
2004-02-03
Bagnell, David (Department: 3672)
Wells
Processes
Electric current or electrical wave energy through earth for...
C166S058000, C166S060000, C166S302000
Reexamination Certificate
active
06684948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to the field of devices for heating a subterranean formation.
2. Background Information
The utility and desirability of applying heat to subterranean formations are well known. There are numerous applications, including oil production and remediation of contaminated soils. In many instances it is desirable to heat thick underground sections as uniformly, efficiently, and economically as possible. There are vast deposits of hydrocarbons all over the world, including oil shales, tar sands, and oil-bearing diatomites that will yield combustible gases and oil when heated. There are thousands of sites that have been contaminated by pollutants that can be driven out of the soil or decomposed in place by the application of heat. There may be numerous other uses for the application of subterranean heat as well, including, but not limited to: the accelerated digestion of landfills, thawing of permafrost, gasification of coal, production of methane hydrates, and others.
A means for heating subterranean formations was invented by Ljungstrom in 1940, U.S. Pat. No. 2,732,195. Ljungstrom's invention pertained to formations of oil shale and used electrical resistance heaters installed in a pattern of vertical bore holes to heat the formation through thermal conduction. When heat was applied to the oil shale formation the waxy hydrocarbon “kerogen” began to break down to yield fuel gases and shale oil. Heat induced pressures in the formation drove these products into collection wells, where they were recovered. The so-called “Ljungstrom Method” was successfully deployed in Sweden during World War II to help alleviate a critical shortage of liquid fuels in that country. Details regarding the Ljungstrom Method have been widely published in journal articles like “Underground Shale Oil Pyrolysis According to the Ljungstrom Method, ” by G. Salomonsson, Swedish Shale Oil Corp.,
IVA
, vol. 24, (1953), No. 3, pp. 118-123. “Production of Shale Oil in Sweden,” by H. E. Linden,
Producer's Monthly
, July, 1948, pp. 29-34. And others.
Since Ljungstrom, there have been numerous inventions for other types of apparatus and methods to heat subterranean formations. These include: gas fired burners—U.S. Pat. No. 2,902,270; elongated porous combustion tubes—U.S. Pat. No. 3,113,623; catalytic heaters—U.S. Pat. No. 3,804,163; electro-heating with electrodes—U.S. Pat. No. 4,412,585; heating with radio frequency electromagnetic radiation (microwaves)—U.S. Pat. No. 4,320,801; flameless combustors—U.S. Pat. No. 5,255,742; circulation of hot combustion gases—U.S. Pat. No. 6,056,057; and nuclear reactor cooling fluids—U.S. Pat. No. 3,237,689.
Many of the above inventions apply to oil shales, oil sands, coal seams or other hydrocarbon formations. Heating has numerous effects which aid in the recovery of a variety of fossil resources: Heat reduces the viscosity of heavy oils, produces fuel gases through distillation, pressurizes underground formations, and forms fractures due to gas and steam pressure and thermal expansion. According to U.S. Pat. No. 5,297,626: “Production of oil in a thermal conduction process is by pressure drive, vaporization and thermal expansion of oil and water trapped within the pores of the formation rock. Oil migrates through small fractures created by the expansion and vaporization of the oil and water.”
One of the great advantages of heating the ground to facilitate resource extraction is the fact that it is a so-called “in-situ” process. In-situ means that the resource ore body is left in place in the ground while the oil, gas, or other desirable products are removed. This has great advantages over mining or other “ex-situ” techniques, which require physical removal of the ore bodies, and extensive processing to separate the desired products from their mineral matrix. Insitu processes minimize capital expenditures and are generally less environmentally disruptive. In-situ processes also tend to be scalable, allowing projects to start small and grow incrementally.
The opposite is frequently true of mining ventures, which can require a minimum size for economical operation. This has especially been the case with hydrocarbon resources like oil shale, where immense mining operations would be required in order to achieve economies of scale that would allow shale oil to be produced at competitive costs. It has been estimated that production of one million barrels of shale oil per day would require mining activity equivalent to all other U.S. mines put together. Building such enormous facilities means taking huge financial risks before the first dollar of revenue can be realized. This fact, together with the environmental complications of such projects, has prevented their being brought to fruition in the past.
In-situ heating of underground formations can also be used to decontaminate polluted soils. U.S. Pat. Nos. 5,318,116 and 5,244,310, for example, disclose methods for decontaminating soils by injecting heat below the surface in order to break down, vaporize, and mobilize pollutants.
All of the previously proposed in-situ methods for applying subterranean heat have suffered from serious disadvantages. For example, those that require inputs of electrical energy, like electrical resistance heaters and microwave electrodes, face serious thermodynamic and economic inefficiencies. According to U.S. Pat. No. 5,297,626: “The high cost of electrical energy is also an impediment to commercial projects using these prior art methods. Conversion of hydrocarbons to electrical energy is typically accomplished at only about 35 percent efficiency and requires a considerable capital investment.”
Essentially, electrically powered heaters trade electricity for heat. The electricity, however, must first be produced, usually through combustion of some fuel. Since typical central power plant efficiencies are only 30-35%, this means that every BTU of heat put in the ground by these methods may require 3 BTU of fuel consumed in power plants. The Ljungstrom Method, for example, requires 24 kilowatt hours (kWh) of power for every gallon of oil produced. Producing 24 kWh of electricity in a central power plant might require 254,000 BTU worth of fuel. Since a gallon of oil typically contains 140,000 BTU, it can be seen that the Ljungstrom Method operated at a loss.
The Ljungstrom Method was used briefly in Sweden only because that country had an abundance of cheap hydropower and an acute shortage of liquid transportation fuels. Other electrically powered systems for ground heating are reportedly less demanding of electricity than the Ljungstrom Method, but are still uneconomic. For example, heating of an oil shale formation by microwaves is reported to yield one gallon of oil for every 9.3 kWh of electricity expended. (R. Mallon,
Economics of Shale Oil Production by Radio Frequency Heating
, Report No. UCRL-52942, Lawrence Livermore Laboratory, May 1980, p. 134.) At prevailing rates of $0.05/kwh, this would translate into a cost of $19.50 per barrel for electricity alone. (These calculations do not take into account the production of noncondensable gases, or other co-products that may or may not have economic value.)
Other subterranean heaters in the prior art attempt to address the inefficiencies inherent in electrically driven systems by burning fuels to produce heat directly. Generally heat from combustion is cheaper than heat from electricity. These systems avoid the intermediate step of producing electricity and therefore are thermodynamically superior, but still suffer from economic shortcomings that have thus far prevented their widespread adoption. Inventions of this type include gas-fired heaters, catalytic heaters, and flameless combustors among others.
Numerous inventions for combustion heaters propose to heat formations by circulating hot gases or other fluids from surface heaters. For example, U.S. Pat. No. 6,056,057 proposes to produce a stream of hot gases in a surface burner and to then circulate those gases in
Bagnell David
Martin Rick
Patent Law Offices of Rick Martin P.C.
Walker Zakiya
LandOfFree
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