Method and apparatus for forming an insulated oil well casing

Details Method and apparatus for forming an insulated oil well casing Method and apparatus for forming an insulated oil well casing

1987-06-18

1988-12-27

Kisliuk, Bruce M.

Wells

With heating, refrigerating or heat insulating means

166 60, 166242, 166380, 138146, 156187, 174120C, 174120SR, 219277, E21B 1916, E21B 3600, F16L 914, H05B 302

Patent

active

047934093

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. The uninsulated portions of joints between segments are covered withan insulator cement in the field and then further covered with a water-impervious tape that overlaps the water-impervious layers on two segments.

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patent: 4412124 (1983-10-01), Kobayashi
patent: 4463805 (1984-08-01), Bingham
patent: 4484627 (1984-11-01), Perkins
patent: 4577664 (1986-03-01), Takahashi et al.
patent: 4665281 (1987-05-01), Kamis
patent: 4665305 (1987-05-01), Shirazawa et al.

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