Patent ID: 7490665
Filing Date: 2009-02-17
Classification: E21B,H05B

Abstract:
1. A heating system configured to heat at least a part of a subsurface formation, comprising: an electrical power supply, wherein the electrical power supply is configured to provide modulated DC; a heater section comprising one or more electrical conductors electrically coupled to the electrical power supply and configured to be placed in an opening in the formation, at least one of the electrical conductors comprising ferromagnetic material; wherein the heater section (a) provides a first heat output when modulated DC is applied to the heater section below a selected temperature, and (b) provides a second heat output approximately at and above the selected temperature during use, the second heat output being reduced compared to the first heat output; the system configured to allow heat to transfer from the heater section to a part of the formation; and the system configured to allow a frequency of the modulated DC to be varied.