Patent ID: 8224165
Filing Date: 2012-07-17
Classification: C07C,E21B,Y10T

Abstract:
1. A heater configured for heating a subsurface formation, comprising: an inner electrical conductor comprising electrically conductive material; a ferromagnetic conductor concentric with the inner electrical conductor, wherein the ferromagnetic conductor at least partially surrounds the inner electrical conductor and is electrically coupled to the inner electrical conductor; and an electrical conductor concentric with the ferromagnetic conductor and the inner electrical conductor, wherein the electrical conductor at least partially surrounds the ferromagnetic conductor and is electrically coupled to the ferromagnetic conductor and the inner electrical conductor, the ferromagnetic conductor being positioned relative to the electrical conductor and having a thickness such that an electromagnetic field produced by time-varying current flow in the ferromagnetic conductor confines a majority of the flow of the electrical current to the electrical conductor at temperatures below a selected temperature; wherein the heater is located in a wellbore in a hydrocarbon containing layer in the subsurface formation, the heater is at least about 10 m in length in the hydrocarbon containing layer, and the heater is configured to provide heat to at least a portion of the hydrocarbon containing layer surrounding the wellbore.