Abstract: Electrical heating system for mineral wells, particularly oil wells, in which the reservoir or "pay zone" is heat stimulated or some well components (e.g., the tubing) are heated, or both, by electrical power supplied to a multi-perforate electrode have the operating efficiency enhanced by effectively terminating the heating electrode, at both its top and bottom, at a distance inwardly of the pay zone equal to at least three times the diameter of the well casing. In some systems the electrical power connection to the main heating electrode is made through a section of the production tubing of the well, with an electrical contactor interconnecting the tubing and the electrode in the level of the pay zone; these systems also provide electrical isolation, within critical height limits, for the production tubing and the pump rod. Delivery of electrical power downhole of the well may be accomplished through an electrical cable, which may or may not be appropriately armored.

Abstract: A method and apparatus for forming an electrically conductive externally insulated casing for an oil well of the type in which the casing carries electrical current to a primary heating electrode positioned downhole, using multiple prefabricated casing segments; each casing segment is a long steel pipe having a female thread coupling on one end and a male thread on the other end. Each segment has an insulator covering, over substantially all of its length, that has a figure of merit (erl)/.DELTA. of no more than 4.times.10.sup.8 so that the shunt impedance of the casing to ground can be kept substantially greater than the spreading resistance of the primary heating electrode. The preferred casing segment insulation is in two layers, including a hard, durarable inner layer subject to water degradation and an outer water-impervious layer usually applied as tape.

Abstract: Heating systems for mineral wells (e.g. oil wells) employ electrical power sources, sometimes operating at relatively high frequencies, that are connected to the well casing and production tubing so as to provide a coaxial line electrical heater projecting down into the well. The heating pattern of the coaxial line is effectively controlled so that most of the power is dissipated as heat, primarily in the tubing, above a depth D above which paraffins or other condensible constituents would tend to condense or otherwise impair the flow of mineral fluid up through the production tubing. The applied electrical power is controlled so that the fluid is kept approximately at or only somewhat above the flow impairment temperature for constituents of the fluid. In some embodiments the system is extended to provide heating of a portion of the deposit formation adjacent to the well.