An electrical heater is provided, the electrical heater being useful for heating soil around a wellbore, and the heater including: a plurality of electrically conductive heater elements within a wellbore, each element spaced from the other elements and located around the circumference of a wellbore; and an electrically insulating filer surrounding the elements within the wellbore; wherein a metal casing around the heater is not present.
This application claims the benefit of U.S. Provisionl Application No. 60/077,160 filed on Mar. 6, 1998, the entire disclosure of which is hereby incorporated by reference.
Methods are described for providing localized heating in an oil well at precise depths to accomplish or expedite specific objectives. The methods involve the use of a heating tool which can be lowered into an oil well to apply heat at a precise depth to achieve a desired result. The specific objectives may include localized heating of a fresh cement slurry to accelerate curing, or localized heating of recently emplaced chemicals which are formulated to be thermally activated. One purpose of such chemicals is to viscosify or increase in gel strength after being pumped into an oil well production zone, in order to restrict the production of unwanted formation fluids such as water.
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.
Certain embodiments provide a system including a heater. The heater includes one or more electrical conductors. The heater is configured to generate a heat output during application of electrical current to the heater. The heater includes a ferromagnetic material. A conduit at least partially surrounds the heater. A fluid is located in a space between the heater and the conduit. The fluid has a higher thermal conductivity than air at standard temperature and pressure (STP) (0.degree. C. and 101.325 kPa). The system is configured to provide (a) a first heat output below a selected temperature when time-varying electrical current is applied to the heater, and (b) a second heat output near or above the selected temperature when time-varying electrical current is applied to the heater.
Certain embodiments provide a heater. The heater includes an inner electrical conductor. A heater section at least partially surrounds the inner electrical conductor. The heater section is configured to generate an electrically resistive heat output during application of time-varying electrical current to the heater section. The heater section includes ferromagnetic material. An outer electrical conductor at least partially surrounds the heater section. An applied time-varying electrical current is configured to propagate through the inner electrical conductor and the outer electrical conductor in substantially the same direction. The applied time-varying electrical current is configured to propagate through the heater section in a substantially opposite direction. The heater provides a first heat output when time-varying electrical current is applied to the heater 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.
Certain embodiments provide a method for treating a subsurface formation. The method includes using heaters to form a heated portion of the subsurface formation. A production conduit is used to direct formation fluid in a vapor phase from the heated portion of the subsurface formation towards a surface of the subsurface formation. Condensate of the vapor phase formation fluid is formed in or near the production conduit. Condensate of the vapor phase formation fluid is diverted to a desired location.
