Conduction heating of hydrocarbonaceous formations

• US 4,545,435 A
• Filed: 04/29/1983
• Issued: 10/08/1985
• Est. Priority Date: 04/29/1983
• Status: Expired due to Fees

• Current Assignee: IIT Research Institute (Alion Science & Technology Corp.)
• Original Assignee: IIT Research Institute (Alion Science & Technology Corp.)
• Inventors: Bridges, Jack E., Taflove, Allen
• Primary Examiner(s): Novosad, Stephen J.
• Assistant Examiner(s): Kisliuk, Bruce M.
• Application Number:
  US06/489,849
• Time in Patent Office: 893 Days
• Field of Search: 166/248, 166/60, 166/272, 166/65 R, 166/50, 166/52, 166/245, 219/10.55 R, 219/10.65, 219/10.81
• US Class Current: 166/248
• CPC Class Codes: E21B 36/04 using electrical heaters
• CPC Class Codes: E21B 43/2401 by means of electricity
• CPC Class Codes: E21B 43/305 comprising at least one inclined or horizontal well
• CPC Class Codes: H05B 3/60 Heating arrangements wherein the heating current flows through granular powdered or fluid material, e.g. for salt-bath furnace, electrolytic heating H05B3/38 takes precedence

Abstract

A waveguide structure is emplanted in the earth to bound a particular volume of an earth formation with a waveguide structure formed of respective rows of discrete elongated electrodes wherein the spacing between rows is greater than the distance between electrodes in a respective row and in the case of vertical electrodes substantially less than the thickness of the hydrocarbonaceous earth formation. Electrical power at no more than a relatively low frequency is applied between respective rows of the electrodes to deliver power to the formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent barren regions to less than a tolerable amount. At the same time the temperature of the electrodes is controlled near the vaporization point of water thereat to maintain an electrically conductive path between the electrodes and the formation.

Claims

1. A method for the in situ heating of earth formations having substantial electrical conductivity, said method comprising

bounding a particular volume of a said earth formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein the active electrode area and the row separation are chosen in reference to the formation thickness to avoid heating barren layers, and

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to deliver power to said formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent regions to less than a predetermined amount,

the electrode spacing and diameters limiting the temperature of said electrodes to near the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation.

2. A method for the in situ heating of earth formations having substantial electrical conductivity, said method comprising

bounding a particular volume of a said earth formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein the active electrode area and the row separation are chosen in reference to the formation thickness to avoid heating barren layers,

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to deliver power to said formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent regions to less than a predetermined amount, and

at the same time controlling the temperature of said electrodes near the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation,

said power being applied to make the formation temperature profile factor c less than 30/Δ

T, where Δ

T is the increase in the temperature of the volume in degrees Celsius and

space="preserve" listing-type="equation">c=kt/(h/2).sup.2

where k is the mean thermal diffusivity of the formation, t is the heating time and h is the thickness of the formation.

3. A method for the in situ heating of earth formations having substantial electrical conductivity, said method comprising

bounding a particular volume of a said earth formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein the active electrode area and the row separation are chosen in reference to the formation thickness to avoid heating barren layers,

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to deliver power to said formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent regions to less than a predetermined amount, and

at the same time controlling the temperature of said electrodes near the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation,

said electrodes being disposed transversely of said formation and the spacing between said rows being less than 0.6 of the thickness of said formation, said power being applied between said rows with one side of the power supply grounded, the grounded said electrodes being longer than said thickness, and the other said electrodes lying wholly within said formation by a least 0.15 of said thickness.

4. A method for the in situ heating of an earth formation having substantial electrical conductivity, said method comprising:

bounding a particular volume of said formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein said electrodes are disposed parallel to and adjacent respective boundaries of said formation and the length and width of the active electrode area are large relative to the thickness of said formation to avoid heating barren layers, and said row of electrodes adjacent the upper boundary of said formation is grounded and extends over a greater area than the ungrounded electrodes to shield the region above the grounded electrodes from leakage fields,

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to substantially maximize the power delivered to said formation while producing relatively uniform heating thereof and thereby moderate the relative loss of heat to adjacent regions, and

at the same time controlling the temperature of said electrodes below the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation.

5. A method according to claim 4 further including grounded electrodes near the surface of the earth for collecting stray currents.

6. A method for the in situ heating of an earth formation having substantial electrical conductivity, said method comprising:

bounding a particular volume of said formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein said electrodes are disposed parallel to and adjacent respective boundaries of said formation and the length and width of the active electrode area are large relative to the thickness of said formation to avoid heating barren layers,

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to substantially maximize the power delivered to said formation while producing relatively uniform heating thereof and thereby moderate the relative loss of heat to adjacent regions, wherein power attenuation along the electrodes with the power applied at one end is no greater than 2 dB, and

at the same time controlling the temperature of said electrodes below the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation.

7. A method for the in situ heating of an earth formation having substantial electrical conductivity, said method comprising:

bounding a particular volume of said formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein said electrodes are disposed parallel to and adjacent respective boundaries of said formation and the length and width of the active electrode area are large relative to the thickness of said formation to avoid heating barren layers,

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to substantially maximize the power delivered to said formation while producing relatively uniform heating thereof and thereby moderate the relative loss of heat to adjacent regions, wherein power attenuation along the electrodes with the power applied substantially equally at both ends of the electrodes is less than 8 dB, and

at the same time controlling the temperature of said electrodes below the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation.

8. A method for the in situ heating of an earth formation having substantial electrical conductivity, said method comprising:

bounding a particular volume of said formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein said electrodes are disposed parallel to and adjacent respective boundaries of said formation and the length and width of the active electrode area are large relative to the thickness of said formation to avoid heating barren layers,

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to substantially maximize the power delivered to said formation while producing relatively uniform heating thereof and thereby moderate the relative loss of heat to adjacent regions, wherein the diameter of the electrodes are sufficiently large and the array of such electrodes is so dense that the I² R losses in the electrodes are small relative to the power dissipated in the formation adjacent the electrodes, and

at the same time controlling the temperature of said electrodes below the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation.

9. A method according to claim 8 wherein the density of the array is increased at the outermost electrodes.

10. A method according to claim 8 wherein the outermost electrodes are of larger diameter than the other electrodes.

11. A method for the in situ heating of earth formations having substantial electrical conductivity, said method comprising:

bounding a particular volume of a said earth formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein the active electrode area and the row separation are chosen in reference to the formation thickness to avoid heating barren layers,

applying electrical power at no more than a relatively low frequency between respective said rows of electrodes to deliver power to said formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent regions to less than a predetermined amount, and

at the same time controlling the temperature of said electrodes near the vaporization point of water thereat to maintain an electrically conductive path between said electrodes and said formation,

said temperature of said electrodes being controlled by providing a heat sink adjacent said electrodes, said heat sink being provided by creating a region of reduced electric field intensity adjacent said rows of electrodes outside said bounded volume, and said region of reduced electric field being created by providing at least two adjacent rows of electrodes at the same potential spaced from each other by a wall sufficiently thick to cool the formation in the vicinity of the respective electrodes during the application of power and sufficiently thin to permit the wall to reach a desired operating temperature via thermal diffusion after the application of power has ended.

12. A method for the in situ heating of earth formations having substantial electrical conductivity, said method comprising

bounding a particular volume of a said earth formation with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein the active electrode area and the row separation are chosen in reference to the formation thickness to avoid heating barren layers, and

applying electrical power at no more than a relatively low frequency for a limited period of time between respective said rows of electrodes to deliver power to said formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent regions to less than a predetermined amount,

at least two adjacent said rows of electrodes being at the same potential and spaced from each other by a wall sufficiently thick to provide thermal capacity for cooling the formation in the vicinity of the respective electrodes during the application of power and sufficiently thin as to be heated to a desired temperature via thermal diffusion after the application of power has ended.