| 摘要 |
Material is thermally extracted from an underground formation with the aid of heat supplied by electrical resistance heaters (21) or by tubing (5, 6) serving as such, or by heated fluid conveyed downhole in pipes (12), which may serve as electrical conductors, or as resistance heaters, or which may be heated downhole. The fluid may be circulated upwardly after passage through a downhole pump unit where the fluid is suitable.
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