WO2007147050A2

WO2007147050A2 - Combined electromagnetic thermal system for natural gas and oil recovery and environmental applications

Info

Publication number: WO2007147050A2
Application number: PCT/US2007/071210
Authority: WO
Inventors: Raymond S. Kasevich
Original assignee: Kasevich Raymond S
Priority date: 2006-06-14
Filing date: 2007-06-14
Publication date: 2007-12-21
Also published as: WO2007147050A3

Abstract

The present invention combines low frequency rotating electromagnetic energy field with subsurface radiofrequency heating to achieve the ability to provide thermal energy under a wide range of temperatures to oil and gas deposits for economic energy recovery and other materials such as toxic wastes for environmental remediation. The combination of the two technologies allows for more cost effective and practical means of thermal energy transfer to selective earth materials.

Description

COMBINED ELECTROMAGNETIC THERMAL SYSTEM FOR NATURAL GAS AND OIL RECOVERY AND ENVIRONMENTAL APPLICATIONS

FIELD OF THE INVENTION

[001] The present invention relates generally to the use of a combination of low frequency rotating electromagnetic energy and radiofrequency energy to heat subsurface oil and gas deposits in situ, thereby enhancing the recovery of such oil and gas. The present invention may also be used to heat subsurface environmental contaminants to facilitate remediation of contaminated soil.

BACKGROUND OF THE INVENTION

[002] There is a growing need for the efficient and cost-effective recovery of oil and natural gas from the earth. Similarly, the rise of the chemical and petrochemical industries has resulted in some case in the introduction of toxic chemicals into the soil, requiring remediation of such contaminated sites by removal of the chemicals before they can damage local flora and fauna or enter the water supply.

[003] A known method of both recovering oil and gas and remediating environmental contamination heating the soil in which they are contained. Heating oil and gas fields facilitates recovery of the oil and gas by steam driving the oil and gas away from the source of the heat (and to a recovery apparatus), while at the same time resulting in a reduction in formation water. Similarly, heating contaminated soil above the boiling point of the toxic chemicals therein causes the chemicals to vaporize, which facilitates collection and condensation for proper disposal.

[004] One current method of heating soil is to bore pairs of holes into the soil and to insert electrodes into those holes. When a voltage is applied between the electrodes, current flows from one electrode, through the soil, and into the other electrode. As the current passes through the soil, it encounters resistance. This resistance results in the generation of heat.

[005] A disadvantage of the foregoing soil heating method is that the soil is heated only along the current path between a pair of electrodes. As a result, the temperature distribution in the soil is uneven. It is true that, given enough time, heat will flow from hot portions of the soil to cooler portions of the soil, thereby equalizing the temperature distribution within the soil. However, the use of such a method is comparatively inefficient and expensive. Further, in some cases, such as when toxic chemicals are migrating, time is of the essence.

[006] The problem of uneven heat distribution in the soil has been addressed by inserting many more pairs of electrodes into the soil. This results in many more subsurface current paths along which soil can be heated. However, this solution results in the need to bore many more holes in the soil. Again, this method is comparatively inefficient and expensive. Further, the mechanical disturbances associated with boring many holes can affect the sub-surface properties of the soil in a way that accelerates the dispersal of toxic chemicals.

[007] The use of a low frequency rotating electromagnetic field such as that described in U.S. Patent No. 6,413,399 to Kasevich to heat the soil represents an improvement over the soil heating systems and methods described above. Such a system evenly heats the soil while minimizing the number of electrodes inserted into the soil. That system is limited, however, in the heat in can generate, hi standard conditions, a low frequency rotating electromagnetic field typically is capable of generating temperatures only as high as 100 degrees Centigrade. Certain applications require higher temperatures to operate effectively. For example, the recovery of heavy crude oil requires temperatures exceeding 100 degrees Centigrade. Furthermore, the remediation of certain toxic chemicals, such as pcb's, requires higher temperatures. [008] Thus, there is a need for an apparatus and method to enhance the recovery of natural gas and oil, as well as remediate contaminated soil, that does not suffer from the drawbacks of the current methods, hi particular, there is a need for a method that is capable of evenly heating soil while minimizing the number of electrodes inserted into the soil, while at the same time being capable of generating greater temperatures where such temperatures are called for.

BRIEF SUMMARY OF THE INVENTION

[009] The present invention combines low frequency rotating electromagnetic energy field with subsurface radiofrequency heating to achieve the ability to provide thermal energy under a wide range of temperatures to oil and gas deposits for economic energy recovery and other materials such as toxic wastes for environmental remediation. The combination of the two technologies allows for more cost effective and practical means of thermal energy transfer to selective earth materials. The low frequency rotating electromagnetic field creates uniform resistive or conductive heating of solids and liquids at temperatures as high as 100 degrees Centigrade within a circular pattern of heat. Higher temperatures (above 100 C) required for oil and gas recovery as well as environmental toxins such as pcb's can be achieved by switching over to the radiofrequency equipment designed to radiate energy into the formation. Conductivity is not required for antenna radiation of thermal energy as it is required for rotating field resistive heating.

[010] The subsurface equipment for both the rotating field resistive heating system and radiofrequency radiation system is configured from vertical, horizontal, or slanted boreholes containing the same electrode design. In other words, a minimum number of small diameter drilled holes only is required with the same borehole electrode utilized for either antenna radiation or conductive or resistive heating of materials outside the borehole. A typical borehole system module would consist of four drilled holes in a pattern where each electrode/antenna containing borehole is at the vertex of an equilateral triangle with different choices on the selection of the area required for heating; the fourth hole being a ground reference electrode located in the center of the triangle. For an area of approximately 50 feet by 50 feet, the total power requirement may be several hundred kVA for the three phase revolving field at 60 Hertz and 25 to 50 kilowatts per borehole for the radiation systems.

[011] Combining the capability of applying a low frequency electromagnetic field and radiofrequency energy results in several advantages. For example, the rotating field of thermal energy may be applied initially to begin the recovery of liquids and gas through steam drive away from the electrode array and thereby provide initial recovery of oil/gas with attendant reduction in formation water. If temperatures above 100 degrees Centigrade are required, than radiofrequency energy may be applied and radiation with much less attenuation will occur giving rise to an expanded zone of heat beyond that established by the revolving field and considerably greater than if the revolving field was not used. Further, by applying the low frequency electromagnetic field first, coking at the antenna boreholes will be prevented with very stable operation of the impedance for oil recovery applications. This insures high radiation efficiency of the antennas. Finally, the employment of the revolving field can help to enhance permeability for more efficient recovery by using the thermal energy to fracture rock in formations such as oil shale. After fracturing, the radiofrequency energy will be employed for more efficient recovery. For remediation sites that have both fractured bedrock and soils, the combination technologies allow for complete remediation without having to employ additional boreholes and additional equipment. [012] In one embodiment of the invention, a system for heating earthen material with a sub-surface rotating field and radiofrequency energy is provided. The system may comprise a first antenna in electrical communication with said earthen material, said first antenna coupled to a first AC voltage source and a radiofrequency generator and being disposed on a circumference of a circle; a second antenna in electrical communication with said earthen material, said second antenna being coupled to a second AC voltage source having a 120 degree phase difference relative to said first AC voltage source and said radiofrequency generator, said second antenna being disposed on said circumference 120 degrees from said first antenna; and a third antenna in electrical communication with said earthen material, said third antenna being coupled to a third AC voltage source having a 120 degree phase difference relative to said second AC voltage source and said radiofrequency generator, said third antenna being disposed on said circumference 120 degrees from said second antenna. [013] In another embodiment of the invention, a method for heating earthen material with a sub-surface rotating field and radiofrequency energy is provided. The method comprises the steps of: inserting first, second, and third antennas along the circumference of a circle, and applying first, second, and third voltages to said first, second, and third antennas respectively, thereby generating a sub-surface rotating electromagnetic field and applying radiofrequency to said first, second, and third antennas, thereby generating radiofrequency energy in said earthen material. [014] While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[015] Fig. 1 is a plan view of the system according to the invention.

[016] Fig. 2 shows the system of the invention from a sub-surface perspective.

[017] Fig. 3 is a perspective view of an electrode antenna for use in the present invention.

DETAILED DESCRIPTION

[018] The oil/gas recovery and environmental remediation system of the present invention generates a sub-surface rotating field that drives currents within a recovery or remediation zone, hi this operation, because the magnitudes of these currents are responsive to the sub-surface field distribution, and because the sub-surface field is a rotating field, the current density within the recovery or remediation zone, when integrated over time, is relatively uniform, and therefore uniformly heats the soil. The system also transfers radiofrequency energy to the recovery/remediation zone to heat the soil to higher temperatures.

[019] FIG. 1 shows a plan view of the recovery or remediation system 10 according to the invention. The illustrated system 10 includes three electrodes/antennas (hereinafter referred to as antennas) 12, 14, and 16 inserted into the earth. These antennas may be, for example, monopole antennas as described in more detail below. Those skilled in the art will understand that any antenna capable of carrying both low frequency currents as well as radiofrequency energy may be used in the invention. Antennas 12, 14, and 16 are typically placed at the vertices of an equilateral triangle 20, and are therefore positioned approximately 120 degrees apart on the circumference of recovery circle 22, which represents the area to which the low frequency electromagnetic energy and radiofrequency energy are applied. To enhance safety, the system can further include a neutral electrode 30 inserted into the earth. This neutral electrode is typically disposed at the center of the recovery circle 22. [020] Antennas 12, 14, and 16 are each coupled to a separate AC voltage source 13, 15, or 17 for the creation of the rotating field resistive heating system. For this purpose, a portion of antennas 12, 14, and 16 are in electrical communication with the soil. First AC voltage source 13 provides a sinusoidal voltage between first antenna 12 and neutral electrode 30, which is in electrical communication with each of antennas 12, 14, and 16. The distance between first antenna 12 and neutral electrode 30 defines the radius of recovery circle 22. Second AC voltage source 15 similarly provides a sinusoidal voltage between second antenna 14 and neutral electrode 30, and third AC voltage source 17 provides a sinusoidal voltage between third antenna 16 and neutral electrode 30. The voltage applied by second voltage source 15 is a sinusoidal voltage having an amplitude equal to that supplied by first voltage source 13 but retarded in phase by 120 degrees. The voltage provided by third voltage source 17 is a sinusoidal voltage identical to that provided by second voltage source 15, but delayed in phase by 120 degrees. Thus, the second and third antennas differ in phase from the first antenna by 120 and 240 degrees, respectively. In a preferred embodiment, the AC voltage sources 13, 15, and 17 operate at 60 Hz for compatibility with supplied line power. [021] As noted, the rotating field resistive heating system typically generates temperatures as high as 100 degrees Centigrade. For higher temperatures, radiofrequency energy is supplied to antennas 12, 14, and 16 by radiofrequency generator 40, which is connected to each antenna by, for example, coaxial cable. [022] FIG. 2 shows the system 10 of FIG. 1 from a sub-surface perspective.

The antennas 12, 14, and 16 and neutral electrode 30 (not shown) are deployed so that they extend into the oil or gas deposit or contaminated soil 50. AC voltage sources 13 and 15 are shown coupled to the electrodes. Oil or gas deposit or contaminated soil 50 overlaps with recovery or remediation zone 52.

[023] In operation, the system first generates a rotating field resistive heating system to heat the soil to temperatures up to 100 degrees Centigrade. First antenna 12 generates a sub-surface electric field having a field distribution given by E₁= E₀ cos(θ) where theta is a radial angle associated with recovery circle 22. Similarly, second and third antennas 14 and 16 generate sub-surface electric fields identical to that generated by the first antenna 12 but retarded in phase by 120 degrees and 240 degrees respectively. These sub-surface fields can be represented as: E₂= E₀ cos(θ-120) and E₃= Eo cos(θ-240) respectively.

[024] The total sub-surface electric field is the superposition of the sub-surface fields generated by the three antennas 12, 14, and 16. This sub-surface field is therefore a rotating field given by: E_tot= 3/2E₀ cos(θ-t) where is the frequency of the voltage waveform applied by the three phase-shifted voltage sources 13, 15, and 17. [025] The three antennas thus cooperate to generate a sub-surface traveling wave propagating in a circumferential direction along recovery circle 22. Because the sub-surface wave traveling wave propagates along in the circumferential direction, it is often referred to as a "rotating field." This sub-surface rotating field drives sub-surface currents in the recovery or remediation zone 52. These currents pass through the oil or gas deposit or contaminated soil 50 between the antennas 12, 14, and 16. As this current traverses oil or gas deposit or contaminated soil 50 having finite conductivity, a portion of the energy carried by the current is transformed into heat. The heat thus generated raises the temperature of the oil or gas or any volatile contaminants present in the soil and thereby reduces their viscosity or hastens their evaporation.

[026] Because the combined field generated by contributions of the three antennas is a rotating field, the current driven by the electric field is more evenly distributed throughout the recovery or remediation zone 52. As a result, the temperature distribution within the zone 52 remains relatively constant during the process, hi addition, because only four antennas are required, there is little likelihood that the boring of holes in the earth will disturb the sub-surface structures so as to disperse the contaminants over a wider region.

[027] The system 10 according to the invention does not need a neutral electrode 30 in order to generate a rotating field for evenly heating zone 52. However, the presence of a neutral electrode 30 is preferable to provide a known destination for currents traversing zone 52. Without a neutral electrode 30, currents flowing within zone 52 may flow outward to nearby structures, thereby posing a threat of personal injury to occupants of those structures. This is of particular importance when the loads on the three underground circuits are unbalanced.

[028] The foregoing embodiment, in which three antennas are excited with voltages phased 120 degrees apart, is advantageous because it reduces the number of holes that must be drilled in the desired region. However, a rotating sub-surface field can be generated using different numbers of antennas having different sub-surface configurations. This can be achieved by exciting the electrodes with voltages having appropriate amplitudes and phases. The derivation of appropriate complex voltages is a mathematical exercise which is essentially the inverse of obtaining the electromagnetic field distribution from known sources.

[029] When temperatures exceeding 100 degrees Centigrade are required due to the nature of the oil, gas, or chemicals in recovery or remediation zone 52, antennas 12, 14, and 16 can be switched to distribute radiofrequency energy. Radiofrequency generator 40 supplies radiofrequency to each of the antennas 12, 14, and 16. The antennas then generate radiofrequency energy in the surrounding soil, thereby heating it beyond 100 degrees Centigrade.

[030] Fig. 3 is a perspective view of an antenna 60 for use in system 10.

Antenna 60 is a monopole antenna adapted to carry both low frequency currents for resistive heating and radiofrequency for hearing by radiofrequency energy. Antenna 60 is adapted to carry low frequency currents by insulating a portion of the antenna with movable insulator 70. Portion 62 of antenna 60 (that with the largest diameter) remains uninsulated, and thereby transmits low frequency currents to the surrounding soil. Portion 62 also acts as the principal radiator for radiofrequency energy. At 60 Hz, portion 62 must be conductively coupled to the earth to insure the flow of currents into the formation. Saline water may be added for this purpose. As an antenna, water is not required nor is it required to be conductively coupled (intimate contact with the borehole wall) since displacement currents operate with antennas. They do not need conductivity to transfer power to the earth materials.

[031] During operation in low frequency mode, current can only flow from the electrically exposed surfaces of the uninsulated portions of antenna 60. Thus, the geometry of the recovery or remediation zone 52 can be readily adjusted by moving insulator 70 and changing the position and the surface area of the electrically exposed surfaces on the uninsulated sections of antenna 60.

Claims

CLAIMS What is claimed is:

1. A system for heating earthen material with a sub-surface rotating field and radiofrequency energy, said system comprising: a first antenna in electrical communication with said earthen material, said first antenna coupled to a first AC voltage source and a radiofrequency generator and being disposed on a circumference of a circle;

a second antenna in electrical communication with said earthen material, said second antenna being coupled to a second AC voltage source having a 120 degree phase difference relative to said first AC voltage source and said radiofrequency generator, said second antenna being disposed on said circumference 120 degrees from said first antenna; and

a third antenna in electrical communication with said earthen material, said third antenna being coupled to a third AC voltage source having a 120 degree phase difference relative to said second AC voltage source and said radiofrequency generator, said third antenna being disposed on said circumference 120 degrees from said second antenna.

2. The system of claim 1 further comprising a neutral electrode in electrical communication with said first, second, and third antennas.

3. The system of claim 2 wherein said neutral electrode is disposed at the center of said circle.

4. The system of claim 1 wherein said first antenna comprises an insulated section and an uninsulated section in electrical communication with said insulated section.

5. The system of claim 4 wherein said first antenna comprises an insulating jacket movable along a longitudinal axis.

6. A method for heating earthen material with a sub-surface rotating field and radiofrequency energy, the method comprising the steps of: inserting first, second, and third antennas along the circumference of a circle; and

applying first, second, and third voltages to said first, second, and third antennas respectively, thereby generating a sub-surface rotating electromagnetic field.; and

applying radiofrequency to said first, second, and third antennas, thereby generating radiofrequency energy in said earthen material.

7. The method of claim 6 wherein said inserting step comprises the step of inserting said first, second, and third antennas 120 degrees apart along said circle.

8. The method of claim 6 wherein said step of applying first, second, and third voltages comprises the steps of applying a phase difference of 120 degrees between said first voltage and said second voltage, and applying a phase difference of 240 degrees between said first voltage and said third voltage.

9. The method of claim 6 further comprising the step of positioning said first, second, and third antennas to generate a heated zone having a specified geometry.

10. The method of claim 6 further comprising the step of providing said first antenna with an insulated section having an insulated surface area and an uninsulated section having an uninsulated surface area, said uninsulated section being in electrical communication with said insulated section.

11. The method of claim 10 further comprising the step of adjusting said insulated surface area and said uninsulated surface area to form a heated zone having a prescribed geometry.

12. The method of claim 11 wherein said step of adjusting said insulated area and said uninsulated area comprises the step of adjusting an uninsulated length associated with said uninsulated section and adjusting an insulated length associated with said insulated section.

13. The method of claim 12 wherein said step of adjusting an uninsulated length comprises the step of translating an insulating jacket along a longitudinal axis of said first electrode.