For the extraction of very heavy oils or bitumen from oil sand or oil shale deposits by means of pipe systems which are introduced through boreholes, the fluidity of the raw materials which are present in a solid consistency has to be increased considerably. This can be achieved by increasing the temperature of the deposit in the reservoir.
If inductive heating is used for this purpose exclusively or in support of the usual SAGD (Steam Assisted. Gravity Drainage) process, the problem arises that adjacent inductors which are supplied with current simultaneously can have a negative effect on one another. For example, adjacent inductors which are supplied with current in opposing directions weaken one another in terms of the thermal energy deposited in the reservoir.
In the German patent applications DE 10 2007 008 292, DE 10 2007 036 832, and DE 10 2007 040 605, individual inductor pairs, i.e. forward and return conductors, are supplied in a predetermined geometric configuration with current in order to heat the reservoir inductively. The current strength is used for adjusting the desired the final output while the phase position is fixed at 180° between adjacent inductors. This supply of current in phase opposition follows necessarily from running an inductor pair comprising forward and return conductor to a generator. In a parallel patent application by the applicant designated “System for the in-situ extraction of a substance comprising hydrocarbons”, among other things, the control of the heat output distribution in an array of inductors is described, this being achieved through the adjustability of the current amplitudes and phase position of adjacent inductor pairs. All previous patent applications assume that the supply of current over lengthy time periods of from days to months undergoes only minor adjustments and that a generator is permanently assigned to an inductor pair.