Temperature limited heaters for heating subsurface formations or wellbores

• US 8,200,072 B2
• Filed: 10/24/2003
• Issued: 06/12/2012
• Est. Priority Date: 10/24/2002
• Status: Expired due to Fees

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Vinegar, Harold J., Sandberg, Chester Ledlie, Harris, Christopher Kelvin, Son, Jaime Santos, Menotti, James Louis, Carl, Fredrick Gordon Jr.
• Primary Examiner(s): CAMPBELL, THOR S
• Application Number:
  US10/693,816
• Publication Number:
  US 20040146288A1
• Time in Patent Office: 3,154 Days
• Field of Search: 392301-306, 392/469, 166 60- 61, 166/302, 219/553
• US Class Current: 392/301
• CPC Class Codes: E21B 36/008 using chemical heat generating means
• CPC Class Codes: E21B 36/02 using burners
• CPC Class Codes: E21B 36/04 using electrical heaters
• CPC Class Codes: E21B 43/24 using heat, e.g. steam injection
• CPC Class Codes: E21B 43/2401 by means of electricity
• CPC Class Codes: H05B 2214/03 Heating of hydrocarbons

Abstract

Systems and methods are described for heating a subsurface formation. Alternating electrical current may be applied to one or more electrical conductors. The electrical conductors may be located in a subsurface formation. The electrical conductors may provide an electrically resistive heat output upon application of the alternating electrical current. At least one of the electrical conductors may include an electrically resistive ferromagnetic material. The electrical conductor may provide a reduced amount of heat above or near a selected temperature. Heat may be allowed to transfer from the electrical conductor to a part of the subsurface formation.

Claims

1. A system configured to heat at least a part of a hydrocarbon containing formation, comprising:

an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation;

an AC power supply;

one or more electrical conductors configured to be electrically coupled to the AC power supply and located in the opening and extending from the surface into the hydrocarbon containing layer, wherein at least one of the electrical conductors comprises a heater section at least partially in the hydrocarbon containing layer, the heater section comprising an electrically resistive ferromagnetic material configured to provide an electrically resistive heat output when AC is applied to the ferromagnetic material, and wherein the heater section is configured to provide a reduced amount of heat near or above a selected temperature during use due to the decreasing AC resistance of the heater section when the temperature of the ferromagnetic material is near or above the selected temperature; and

wherein the system is configured to allow heat to transfer from the heater section such that heat transfers from the heater section to hydrocarbons in the hydrocarbon containing layer to at least mobilize some hydrocarbons in the layer.

2. The system of claim 1, wherein the heater section automatically provides a reduced amount of heat above or near the selected temperature.

3. The system of claim 1, wherein at least a portion of the heater section is positionable adjacent to an overburden of the formation to heat at least a part of the overburden to inhibit condensation of vapors in a wellbore passing through the overburden.

4. The system of claim 1, wherein at least a portion of the heater section is positionable adjacent to hydrocarbon material in the formation to raise a temperature of at least some of the hydrocarbon material to or above a pyrolysis temperature.

5. The system of claim 1, wherein the system is configured to allow heat to transfer to the hydrocarbon layer to pyrolyze at least some hydrocarbons in the formation.

6. The system of claim 1, wherein the subsurface formation comprises contaminated soil, and wherein the system is configured to decontaminate at least a portion of the contaminated soil.

7. The system of claim 1, wherein the system comprises three or more electrical conductors, and wherein at least three of the electrical conductors are configured to be electrically connected in a three-phase configuration.

8. The system of claim 1, wherein the heater section is configured to provide the reduced amount of heat without controlled adjustment of the AC.

9. The system of claim 1, wherein the heater section is configured to exhibit an increase in operating temperature of less than about 1.5°

C. above or near a selected operating temperature when a thermal load proximate the heater section decreases by about 1 watt per meter.

10. The system of claim 1, further comprising an oxidation heater placed in the opening in the formation.

11. The system of claim 10, wherein the oxidation heater comprises a natural distributed combustor.

12. The system of claim 10, wherein the oxidation heater comprises a flameless distributed combustor.

13. The system of claim 10, wherein at least one of the electrical conductors is configured to provide heat to initiate an oxidation reaction in the oxidation heater during use.

14. The system of claim 10, wherein the selected temperature is above an initiation temperature for an oxidation reaction to commence in the oxidation heater, and wherein the selected temperature is below an operating temperature of the oxidation heater during use.

15. The system of claim 1, further comprising a highly electrically conductive material coupled to at least a portion of the ferromagnetic material of an electrical conductor, wherein AC applied to the electrical conductor substantially flows through the ferromagnetic conductor when a temperature of the ferromagnetic conductor is below the selected temperature, and wherein the AC applied to the conductor is configured to flow through the highly electrically conductive material when the temperature of the ferromagnetic conductor is near or above the selected temperature.

16. The system of claim 1, wherein the ferromagnetic material comprises an elongated material, wherein the system further comprises an elongated highly electrically conductive material, and wherein at least about 50% of the elongated material is electrically coupled to the elongated highly electrically conductive material.

17. The system of claim 1, wherein at least one of the electrical conductors is configured to provide a reduced amount of heat above or near the selected temperature that is about 20% or less of the heat output at about 50°

C. below the selected temperature.

18. The system of claim 1, wherein the heater section is configured such that the decreased AC resistance through the heater section above or near the selected temperature is about 20% or less than the AC resistance at about 50°

C. below the selected temperature.

19. The system of claim 1, wherein the AC resistance of the heater section above or near the selected temperature is about 80% or less of the AC resistance at about 50°

C. below the selected temperature.

20. The system of claim 1, wherein the AC resistance of the heater section decreases above the selected temperature to provide the reduced amount of heat.

21. The system of claim 1, wherein the heater section is configured to automatically exhibit the decreased AC resistance above or near a selected temperature.

22. The system of claim 1, further comprising a non-ferromagnetic material coupled to the ferromagnetic material, wherein the non-ferromagnetic material has a higher electrical conductivity than the ferromagnetic material.

23. The system of claim 1, further comprising a second ferromagnetic material coupled to the ferromagnetic material.

24. The system of claim 1, wherein the selected temperature is approximately the Curie temperature of the ferromagnetic material.

25. The system of claim 1, wherein at least one of the electrical conductors is electrically coupled to the earth, and wherein electrical current is propagated from the electrical conductor to the earth.

26. The system of claim 1, wherein the heater section is elongated, and wherein the reduced amount of heat is less than about 400 watts per meter of length of the heater section.

27. The system of claim 1, wherein the heater section is elongated, and wherein the heat output from the ferromagnetic material is greater than about 400 watts per meter of length of the heater section when the temperature of the ferromagnetic material is below the selected temperature during use.

28. The system of claim 1, wherein the ferromagnetic material has a turndown ratio of at least about 2 to 1.

29. The system of claim 1, further comprising a deformation resistant container configured to contain at least one electrical conductor, and wherein the selected temperature is chosen such that the deformation resistant container has a creep-rupture strength of at least about 3000 psi at 100,000 hours at the selected temperature.

30. The system of claim 1, wherein one or more electrical conductors comprise two or more electrical conductors and an electrically insulating material placed between at least two of the electrical conductors.

31. The system of claim 1, wherein the ferromagnetic material comprises iron, nickel, chromium, cobalt, tungsten, or a mixture thereof.

32. The system of claim 1, wherein the ferromagnetic material comprises a mixture of iron and nickel.

33. The system of claim 1, wherein the ferromagnetic material comprises a mixture of iron and cobalt.

34. The system of claim 1, wherein the system is configured such that the ferromagnetic material has a thickness of at least about ¾

of a skin depth of the AC at the Curie temperature of the ferromagnetic material.

35. The system of claim 1, wherein the system is configured such that the ferromagnetic material has a thickness of at least about ¾

of a skin depth of the AC at the Curie temperature of the ferromagnetic material, and wherein the ferromagnetic material is coupled to a material that is more conductive that the ferromagnetic material such that the coupled materials exhibit a greater conductivity at the Curie temperature of the ferromagnetic material than the ferromagnetic material with the same thickness as the coupled materials.

36. The system of claim 1, wherein the system is configured such that the ferromagnetic material has a thickness of at least about a skin depth of the AC at the Curie temperature of the ferromagnetic material.

37. The system of claim 1, wherein the ferromagnetic material comprises two or more ferromagnetic materials with different Curie temperatures.

38. The system of claim 1, wherein at least one of the electrical conductors comprises ferromagnetic material and non-ferromagnetic electrically conductive material.

39. The system of claim 1, wherein at least a portion of the electrically resistive ferromagnetic material is located proximate a relatively rich hydrocarbon containing layer of the formation.

40. The system of claim 1, wherein the ferromagnetic material is coupled to a corrosion resistant material.

41. The system of claim 1, wherein at least one of the electrical conductors is part of an insulated conductor heater.

42. The system of claim 1, wherein at least one of the electrical conductors is part of a conductor-in-conduit heater.

43. The system of claim 1, wherein the ferromagnetic material is coupled to a material that is more conductive than the ferromagnetic material, and wherein thicknesses of both materials and skin depth characteristics of the ferromagnetic material are configured to provide a selected resistance profile as a function of temperature.

44. The system of claim 1, wherein at least a portion of at least one of the electrical conductors comprises a relatively flat AC resistance profile in a temperature range between about 100°

C. and 750°

C.

45. The system of claim 1, wherein at least a portion of at least one of the electrical conductors comprises a relatively flat AC resistance profile in a temperature range between about 100°

C. and 700°

C. and a relatively sharp resistance profile at a temperature above about 700°

C. and less than about 850°

C.

46. The system of claim 1, wherein at least a portion of at least one of the electrical conductors comprises a relatively flat AC resistance profile in a temperature range between about 300°

C. and 600°

C.

47. The system of claim 1, wherein at least a portion of at least one electrically resistive ferromagnetic material is longer than about 10 m.

48. The system of claim 1, wherein the system is configured to sharply reduce the heat output at or near the selected temperature.

49. The system of claim 1, wherein at least one of the electrical conductors comprises an electrically resistive ferromagnetic material drawn together with or against a material with a higher conductivity than the ferromagnetic material.

50. The system of claim 1, wherein at least one of the electrical conductors comprises an elongated conduit comprising a center portion and an outer portion, and wherein the center portion comprises iron and has a diameter of at least about 0.5 cm.

51. The system of claim 1, wherein at least one of the electrical conductors comprises a composite material, wherein the composite material comprises a first material with a resistance that decreases when the first material is heated to the selected temperature, wherein the composite material comprises a second material that is more electrically conductive than the first material, and wherein the first material is coupled to the second material.

52. The system of claim 1, wherein the reduced amount of heat comprises a heating rate lower than the rate at which the formation will absorb or transfer heat, thereby inhibiting overheating of the formation.

53. The system of claim 1, wherein at least one of the electrical conductors is elongated and configured such that only electrically resistive sections at or near the selected temperature will automatically reduce the heat output.

54. The system of claim 1, wherein the system is configured such that an AC resistance of at least one of the electrical conductors increases with an increase in temperature up to the selected temperature.

55. The system of claim 1, wherein the system is configured such that an AC resistance of at least one of the electrical conductors decreases with an increase in temperature above the selected temperature.

56. The system of claim 1, wherein the system is configured to apply AC of at least about 70 amps to at least one of the electrical conductors.

57. The system of claim 1, wherein the system is configured to apply AC at about 180 Hz.

58. The system of claim 1, wherein the system is configured to apply AC at about 60 Hz.

59. The system of claim 1, wherein the ferromagnetic material is positioned in an opening in the formation, and wherein at least a portion of the opening in the formation adjacent to the ferromagnetic material comprises an uncased wellbore.

60. The system of claim 1, wherein the ferromagnetic material is configured to radiatively heat the formation.

61. The system of claim 1, wherein at least one of the electrical conductors is located in an overburden of the formation.

62. The system of claim 1, wherein at least one of the electrical conductors is coupled to a cable, and wherein the cable comprises a plurality of copper wires coated with an oxidation resistant alloy.

63. A method for heating a hydrocarbon containing formation, comprising:

applying AC to one or more electrical conductors located in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein providing the AC provides an electrically resistive heat output from the electrical conductors, wherein at least one of the electrical conductors comprises an electrically resistive ferromagnetic material that provides heat when AC flows through the electrically resistive ferromagnetic material, and wherein such electrical conductor comprising electrically resistive ferromagnetic material provides a reduced amount of heat above or near a selected temperature; and

allowing the heat to transfer from the electrically resistive ferromagnetic material to hydrocarbons in the hydrocarbon containing layer to at least mobilize some hydrocarbons in the layer.

64. The method of claim 63, wherein the electrically resistive ferromagnetic material automatically provides a selected reduced amount of heat above or near a selected temperature.

65. The method of claim 63, further comprising placing one or more of the electrical conductors in a wellbore in the formation.

66. The method of claim 63, wherein an AC resistance of the ferromagnetic material decreases above the selected temperature to provide the reduced amount of heat.

67. The method of claim 63, wherein a thickness of the ferromagnetic material is greater than about ¾

of a skin depth of the AC at the Curie temperature of the ferromagnetic material.

68. The method of claim 63, wherein the selected temperature is approximately the Curie temperature of the ferromagnetic material.

69. The method of claim 63, wherein the selected temperature is within about 50°

C. of the Curie temperature of the ferromagnetic material.

70. The method of claim 63, further comprising heating at least some hydrocarbons in the hydrocarbon containing layer such that at least some of the hydrocarbons are pyrolyzed.

71. The method of claim 63, wherein one or more of the electrical conductors are located in a wellbore, and further comprising providing a reduced amount of heat of less than about 400 watts per meter of length of the wellbore while one or more of the electrical conductors are above or near the selected temperature.

72. The method of claim 63, wherein one or more of the electrical conductors are located in a wellbore, and further comprising providing a heat output of greater than about 400 watts per meter of length of the wellbore while one or more of the electrical conductors are below the selected temperature.

73. The method of claim 63, further comprising controlling the amount of current applied to one or more of the electrical conductors to control the amount of heat provided by the ferromagnetic material.

74. The method of claim 63, further comprising applying an AC of at least about 70 amps to the electrical conductors.

75. The method of claim 63, further comprising applying an AC of at least about 100 amps to the electrical conductors.

76. The method of claim 63, further comprising applying the AC at a frequency of about 180 Hz.

77. The method of claim 63, wherein the heat transfers radiatively from at least one of the electrical conductors to at least a part of the formation.

78. The method of claim 63, further comprising providing a relatively constant heat output when an electrical conductor is in a temperature range between about 300°

C. and 600°

C.

79. The method of claim 63, further comprising providing a relatively constant heat output when an electrical conductor is in a temperature range between about 100°

C. and 750°

C.

80. The method of claim 63, further comprising providing a heat output from at least one of the electrical conductors, wherein an AC resistance of one or more of such electrical conductors above or near the selected temperature is about 80% or less of the AC resistance of such one or more electrical conductors at about 50°

C. below the selected temperature.

81. The method of claim 63, further comprising providing an initial electrically resistive heat output when the electrical conductor providing the heat output is at least about 50°

C. below the selected temperature, and automatically providing the reduced amount of heat above or near the selected temperature.

82. The method of claim 63, wherein the subsurface formation comprises contaminated soil, and further comprising using the provided heat to decontaminate the soil.

83. The method of claim 63, wherein at least one of the electrical conductors is electrically coupled to the earth, and further comprising propagating electrical current from at least one of the electrical conductors to the earth.

84. The method of claim 63, further comprising producing a mixture from the formation, wherein the produced mixture comprises condensable hydrocarbons having an API gravity of at least about 25°

.

85. The method of claim 63, further comprising controlling a pressure in at least a part of the formation, wherein the controlled pressure is at least about 2.0 bars absolute.

86. The method of claim 63, further comprising controlling formation conditions such that a produced mixture comprises a partial pressure of H₂ greater than about 0.5 bars.

87. The method of claim 63, further comprising altering a pressure in the formation to inhibit production of hydrocarbons having carbon numbers greater than about 25.

88. The method of claim 63, further comprising controlling the provided heat to inhibit production of hydrocarbons from the formation having carbon numbers greater than about 25.

89. The method of claim 63, further comprising heating at least a portion of the hydrocarbon containing layer to a minimum pyrolysis temperature of about 270°

C.

90. The method of claim 63, further comprising controlling a skin depth in the ferromagnetic material by controlling a frequency of the applied AC.

91. The method of claim 63, further comprising increasing the AC applied to at least one of the electrical conductors as the temperature of such electrical conductors increases, and continuing to do so until the temperature is at or near the selected temperature.

92. The method of claim 63, further comprising controlling an amount of current applied to at least one of the electrical conductors to control an amount of heat output from such electrical conductors.

93. The method of claim 63, further comprising increasing an amount of current applied to at least one of the electrical conductors to decrease an amount of heat output from such electrical conductors.

94. The method of claim 63, further comprising decreasing an amount of current applied to at least one of the electrical conductors to increase an amount of heat output from such electrical conductors.

95. The method of claim 63, further comprising producing fluids from the formation, and producing refined products from the produced fluids.

96. The method of claim 63, further comprising producing fluids from the formation, and producing a blending agent from the produced fluids.

97. The method of claim 63, further comprising providing heat from at least one of the electrical conductors to fluids in a wellbore in the formation.

98. The method of claim 63, further comprising producing fluids from the formation, and blending the produced fluids with hydrocarbons having an API gravity below about 15°

.

99. A method for heating a hydrocarbon containing formation, comprising:

applying AC to one or more electrical conductors located in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein at least one of the electrical conductors comprises one or more electrically resistive sections;

providing an electrically resistive heat output from at least one of the electrically resistive sections, wherein such electrically resistive sections provide a reduced amount of heat above or near a selected temperature that is about 20% or less of the heat output at about 50°

C. below the selected temperature; and

allowing the heat to transfer from at least one of the electrically resistive sections to hydrocarbons in the hydrocarbon containing layer to at least mobilize some hydrocarbons in the layer.

100. The method of claim 99, further comprising applying the AC at a frequency of about 180 Hz.

101. The method of claim 99, further comprising placing one or more of the electrical conductors in the opening.

102. The method of claim 99, further comprising providing an initial electrically resistive heat output when the electrically resistive section providing the heat output is at least about 50°

C. below the selected temperature, and automatically providing the reduced amount of heat above or near the selected temperature.

103. The method of claim 99, further comprising providing a reduced amount of heat above or near the selected temperature that is less than about 20% of the heat output at about 40°

C. below the selected temperature.

104. The method of claim 99, further comprising providing a reduced amount of heat above or near the selected temperature that is less than about 20% of the heat output at about 30°

C. below the selected temperature.

105. The method of claim 99, further comprising providing a reduced amount of heat above or near the selected temperature that is less than about 15% of the heat output at about 50°

C. below the selected temperature.

106. The method of claim 99, further comprising providing a reduced amount of heat above or near the selected temperature that is less than about 10% of the heat output at about 50°

C. below the selected temperature.

107. The method of claim 99, further comprising allowing the heat to transfer radiatively from at least one of the electrically resistive sections to at least a part of the formation.

108. The method of claim 99, wherein at least one of the electrically resistive sections comprises ferromagnetic material, and wherein the selected temperature is approximately the Curie temperature of the ferromagnetic material.

109. The method of claim 99, wherein at least one of the electrically resistive sections comprises ferromagnetic material, and wherein the selected temperature is within about 50°

C. of the Curie temperature of the ferromagnetic material.

110. The method of claim 99, further comprising providing a relatively constant heat output from one or more of the electrically resistive sections when such electrically resistive sections are in a temperature range between about 100°

C. and about 750°

C.

111. The method of claim 99, further comprising automatically decreasing an AC resistance of at least one of the electrically resistive sections when such an electrically resistive section is above the selected temperature to provide the reduced amount of heat above the selected temperature.

112. The method of claim 99, further comprising heating at least some hydrocarbons in the hydrocarbon containing layer to pyrolyze at some of the hydrocarbons in the layer.

113. The method of claim 99, further comprising positioning at least one of the electrically resistive sections proximate a relatively rich zone of the formation.

114. The method of claim 99, further comprising providing a reduced amount of heat of less than about 400 watts per meter of length of the opening above or near the selected temperature.

115. The method of claim 99, further comprising applying AC of at least about 70 amps to at least one of the electrical conductors.

116. A method for heating a hydrocarbon containing formation, comprising:

applying a current to one or more electrical conductors located in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein at least one of the electrical conductors comprises one or more electrically resistive sections;

providing an electrically resistive heat output from at least one of the electrically resistive sections, wherein such electrically resistive sections provide a reduced amount of heat above or near a selected temperature that is about 20% or less of the heat output at about 50°

C. below the selected temperature; and

allowing the heat to transfer from at least one of the electrically resistive sections to hydrocarbons in the hydrocarbon containing layer to at least mobilize some hydrocarbons in the layer.

117. The method of claim 116, further comprising applying alternating current to the one or more electrical conductors.

118. The method of claim 116, further comprising applying direct current to the one or more electrical conductors.

119. The method of claim 116, further comprising placing one or more of the electrical conductors in the opening.

120. The method of claim 116, further comprising providing an initial electrically resistive heat output when the electrically resistive section providing the heat output is at least about 50°

C. below the selected temperature, and automatically providing the reduced amount of heat above or near the selected temperature.

121. The method of claim 116, further comprising providing a reduced amount of heat above or near the selected temperature that is less than about 20% of the heat output at about 40°

C. below the selected temperature.

122. The method of claim 116, further comprising providing a reduced amount of heat above or near the selected temperature that is less than about 20% of the heat output at about 30°

C. below the selected temperature.

123. The method of claim 116, further comprising allowing the heat to transfer radiatively from at least one of the electrically resistive sections to at least a part of the formation.

124. The method of claim 116, further comprising automatically decreasing an AC resistance of at least one of the electrically resistive sections when such an electrically resistive section is above the selected temperature to provide the reduced amount of heat above the selected temperature.

125. The method of claim 116, further comprising automatically increasing a resistance of at least one of the electrically resistive sections when such an electrically resistive section is above the selected temperature to provide the reduced amount of heat above the selected temperature.

126. The method of claim 116, further comprising automatically increasing a resistance of at least one of the electrically resistive sections by a factor of at least about 4 when such an electrically resistive section is above the selected temperature to provide the reduced amount of heat above the selected temperature.

127. The method of claim 116, further comprising automatically increasing a resistance of at least one of the electrically resistive sections when such an electrically resistive section is above the selected temperature to provide the reduced amount of heat above the selected temperature such that electrical current propagates through at least one other electrically resistive section.

128. The method of claim 116, further comprising heating at least some hydrocarbons in the hydrocarbon containing layer to pyrolyze at some of the hydrocarbons in the layer.

129. A method for heating a hydrocarbon containing formation, comprising:

applying AC to one or more electrical conductors located in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein at least one of the electrical conductors comprises an electrically resistive ferromagnetic material that provides an electrically resistive heat output when AC is applied to the ferromagnetic material, and wherein AC is applied when the ferromagnetic material is about 50°

C. below a Curie temperature of the ferromagnetic material to provide an initial electrically resistive heat output;

allowing the temperature of the ferromagnetic material to approach or rise above the Curie temperature of the ferromagnetic material;

allowing the heat output from at least one of the electrical conductors to decrease below the initial electrically resistive heat output as a result of a change in AC resistance of such electrical conductor caused by the temperature of the ferromagnetic material approaching or rising above the Curie temperature of the ferromagnetic material; and

allowing heat to transfer from the electrical conductors to hydrocarbons in the hydrocarbon containing layer to at least mobilize some hydrocarbons in the layer.

130. The method of claim 129, further comprising applying AC at a frequency of about 180 Hz.

131. The method of claim 129, further comprising placing one or more of the electrical conductors in the opening.

132. The method of claim 129, wherein the decreased heat output is less than about 50% of the initial heat output.

133. The method of claim 129, wherein the decreased heat output is less than about 20% of the initial heat output.

134. The method of claim 129, further comprising allowing the heat to transfer radiatively from at least one of the electrical conductors to at least a part of the formation.

135. The method of claim 129, further comprising heating at least some hydrocarbons in the hydrocarbon containing layer to pyrolyze at some of the hydrocarbons in the layer.

136. The method of claim 129, further comprising producing at least some fluids from the formation.

137. The method of claim 129, wherein the declined heat output is less than about 400 watts per meter of length of the opening.

138. The method of claim 129, further comprising applying AC of at least about 70 amps to at least one of the electrical conductors.

139. A system configured to heat a part of a hydrocarbon containing formation, comprising:

a conduit configured to be placed in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein the conduit is configured to allow fluids to be produced from the formation;

one or more electrical conductors configured to be placed in the opening in the formation, wherein at least one of the electrical conductors comprises a heater section, the heater section comprising an electrically resistive ferromagnetic material configured to provide an electrically resistive heat output when AC is applied to the ferromagnetic material, wherein the ferromagnetic material provides a reduced amount of heat above or near a selected temperature during use, and wherein the reduced heat output inhibits a temperature rise of the ferromagnetic material above a temperature that causes undesired degradation of hydrocarbon material adjacent to the ferromagnetic material; and

wherein the system is configured to allow heat to transfer from the heater section to a part of the formation such that the heat mobilizes at least some fluids in the formation and/or fluids at, near, and/or in the opening.

140. A method for treating a hydrocarbon containing formation, comprising:

applying AC to one or more electrical conductors located in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein providing the AC to the electrical conductors provides an electrically resistive heat output, wherein at least one of the electrical conductors comprises an electrically resistive ferromagnetic material that provides heat when AC flows through the electrically resistive ferromagnetic material, and wherein the electrically resistive ferromagnetic material provides a reduced amount of heat above or near a selected temperature;

allowing heat to transfer from the electrical conductors to hydrocarbons in the hydrocarbon containing layer to at least mobilize some hydrocarbons in the layer;

allowing the heat to transfer from the electrically resistive ferromagnetic material to a part of the formation so that a viscosity of fluids at or near the opening in the formation is reduced; and

producing the fluids through the opening.

141. A method for treating a hydrocarbon containing formation, comprising:

applying AC to one or more electrical conductors located in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein providing the AC to the electrical conductors provides an electrically resistive heat output, wherein at least one of the electrical conductors comprises an electrically resistive ferromagnetic material that provides heat when AC flows through the electrically resistive ferromagnetic material, and wherein the electrically resistive ferromagnetic material provides a reduced amount of heat above or near a selected temperature;

allowing heat to transfer from the electrical conductors to hydrocarbons in the hydrocarbon containing layer to at least mobilize some hydrocarbons in the layer;

allowing the heat to transfer from the electrically resistive ferromagnetic material to a part of the formation to enhance radial flow of fluids from portions of the formation surrounding the opening to the opening; and

producing the fluids through the opening.

142. A method for heating a hydrocarbon containing formation, comprising:

applying AC to one or more electrical conductors located in an opening extending from a surface of the earth into a hydrocarbon containing layer in the formation, wherein at least one of the electrical conductors comprises one or more electrically resistive sections;

providing a heat output from at least one of the electrically resistive sections, wherein such electrically resistive sections provide a reduced amount of heat above or near a selected temperature that is about 20% or less of the heat output at about 50°

C. below the selected temperature;

allowing the heat to transfer from at least one of the electrically resistive sections to at least a part of the layer such that a temperature in the layer at or near the opening is maintained between about 150°

C. and about 250°

C. to reduce a viscosity of fluids at or near the opening in the layer; and

producing the reduced viscosity fluids through the opening.