FIELD: oil and gas producing industry, particularly, downhole electric heaters of bottom-hole zone of oil-gas- bearing formation; applicable in bottom-hole cleaning and increase of efficiency of oil and gas withdrawal from formation. SUBSTANCE: device A.C. heater includes sealed conducting cylindrical body with end piece partially filled with salt, alkali or acid solution. There are lead-in with current-carrying cable and electric heating member in form of insulated from body current-carrying rod with end piece. External surface of end piece follows shape of internal surface of hollow sealed current-carrying cylindrical body. End piece of electric heating member is inserted into salt, alkali or acid solution insulated from A.C. heater. D.C. electrode has roller and/or plate centralizers coming in contact with casing string during motion of downhole electric heater along oil-gas-bearing formation. Applied to electrode is D.C. positive charge from 10 to 500A and voltage of 150-800V. D.C. electrode is located above or under A. C. heater. Surface of roller centralizers of D.C. electrode coming in contact with casing string is smooth or ribbed. D.C. electrode roller centralizers coming in contact with casing string are spring-loaded. D.c. electrode plate centralizers coming in contact with casing string are springy. Number of roller or plate centralizers of D.C. electrode amounts from 4 to 12. EFFECT: increased versatility of electric heater, efficiency of removal of paraffin and resinous deposits, prevented their formation in zone of oil-gas-bearing formation, eliminated water cones and increased recovery of oil and gas. 6 cl, 1 dwg
