A hydrocarbon containing formation may be treated using an in situ thermal process. A mixture of hydrocarbons, H.sub.2, and/or other formation fluids may be produced from the formation. Heat may be applied to the formation to raise a temperature of a portion of the formation to a pyrolysis temperature. A formation to be treated may produce a relatively large amount of condensable hydrocarbons and/or a relatively large amount of non-condensable hydrocarbons. The formation to be treated may be chosen based on initial hydrocarbon to carbon ratio of the formation.
PRIORITY CLAIM
This application claims priority to U.S. Provisional Application No. 60/199,215 entitled "In Situ Energy Recovery," filed Apr. 24, 2000, U.S. Provisional Application No. 60/199,214 entitled "In Situ Energy Recovery From Coal," filed Apr. 24, 2000, and U.S. Provisional Application No. 60/199,213 entitled "Emissionless Energy Recovery From Coal," filed Apr. 24, 2000. The above-referenced provisional applications are hereby incorporated by reference as if fully set forth herein.
A oil shale formation may be treated using an in situ thermal process. A mixture of hydrocarbons, H.sub.2, and/or other formation fluids may be produced from the formation. Heat may be applied to the formation to raise a temperature of a portion of the formation to a pyrolysis temperature. Heat sources may be used to heat the formation. The heat sources may be positioned within the formation in a selected pattern.
A system for reducing heat load applied to a frozen barrier by a heated formation is described. The system includes heat interceptor wells positioned between the heated formation and the frozen barrier. Fluid is positioned in the heat interceptor wells. Heat transfers from the formation to the fluid to reduce the heat load applied to the frozen barrier.
A heater may include an electrical conductor. Applying alternating current to the electrical conductor may generate resistively heat the electrical conductor. The electrical conductor may include an electrically resistive ferromagnetic material. The ferromagnetic material may at least partially surround a non-ferromagnetic material. The heater may provide a reduced amount of heat above or near a selected temperature. A conduit may at least partially surround the electrical conductor. A centralizer may maintain a separation distance between the electrical conductor and the conduit.
A method for treating a hydrocarbon containing formation is described. The method may include providing heat from one or more heaters to at least a portion of the formation. At least one heater may be located in at least one wellbore in the formation. At least one wellbore may be sized, at least in part, based on a determination of formation expansion caused by heating of the formation so that formation expansion caused by heating of the formation is not sufficient to cause substantial deformation of one or more heaters in the sized wellbores. The ratio of the outside diameter of a heater to the inside diameter of a wellbore may be less than about 0.75. In certain embodiments, heat may transfer from the one or more heaters to a part of the formation. In some embodiments, a mixture may be produced from the formation.
Certain embodiments provide a system configured to heat a subsurface formation. The system includes an electrical power supply. A heater section includes one or more electrical conductors electrically coupled to the electrical power supply. At least one of the electrical conductors includes ferromagnetic material. The heater section provides a first heat output when time-varying electrical current is applied to the heater section below a selected temperature, and a second heat output approximately at and above the selected temperature during use. The second heat output is reduced compared to the first heat output. The system is configured to allow heat to transfer from the heater section to a part of the formation. The electrical power supply is configured to provide a relatively constant amount of time-varying electrical current that remains within about 15% of a selected constant current value when a load of the electrical conductors changes.
