Patent Publication Number: US-10774629-B2

Title: Apparatus and methods for enhancing petroleum extraction

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/508,423, filed on Oct. 7, 2014, entitled “APPARATUS AND METHODS FOR ENHANCING PETROLEUM EXTRACTION”, the entire contents of which are hereby incorporated by reference herein for all purposes. 
    
    
     FIELD 
     The present subject-matter relates to apparatus and methods for enhancing the extraction of hydrocarbons from an underground reservoir. 
     BACKGROUND OF THE INVENTION 
     The extraction of hydrocarbons can be enhanced through the heating of shale oil, heavy oil, oil sand, or carbonate rock reservoirs with electromagnetic (EM) radiation in the radio frequency (RF) range. This is normally called “RF heating” and is generally implemented using a radiating element, located in the reservoir, to radiate an electromagnetic RF field (i.e. modulated at frequencies between 10 kHz to 100 MHz) into the reservoir. RF heating can typically allow for deeper and faster heat penetration than known steam-assisted technologies and can be implemented with simpler surface infrastructure. In addition, RF heating technology can potentially provide improved energy efficiently since it is an all-electrical operation and uses less energy than steam technologies. 
     However, known RF heating techniques are not well suited to the scenarios where the radiating element is separated from the RF power generator by a considerable distance, which may be due to the depth of the well, or where the well is horizontal and is 200 meters long or more. The long distance and limited diameter of the well, which in turn limits the available cross-section size of the transmission lines carrying the RF power to the radiating element, may lead to considerable loss of RF power before it reaches the radiating element. Further, the limited diameter of the well, and hence of the transmission lines, limits the available maximum RF power that can be transmitted down-hole. This makes it very difficult, if not impossible, to deliver to the radiating element a substantial amount of RF power, necessary for the extraction of the hydrocarbons using RF heating. 
     SUMMARY 
     In a first aspect, an apparatus for enhancing the extraction of hydrocarbons from an underground reservoir using a well is provided. In at least one embodiment, the apparatus may comprise a power source operable to supply periodic electrical power at a first frequency; at least one impulse generator unit operable to convert the periodic electrical power at the first frequency into periodic electrical power at a second frequency and to couple electromagnetic energy generated by the periodic electrical power at the second frequency into the reservoir, the second frequency being at least ten times higher than that of the first frequency; and a conducting cable being operatively coupled between the power source and the at least one impulse generator unit. 
     In at least one embodiment, the impulse generator unit comprises at least one frequency conversion unit operable to convert the periodic electrical power at the first frequency into periodic electrical power at the second frequency; and at least one energy coupling unit operable to couple electromagnetic energy generated by the periodic electrical power at the second frequency into the reservoir. 
     In at least one embodiment, the apparatus may also comprise a pipe; wherein at least one portion of the conducting cable is contained within the pipe; and at least one portion of the impulse generator unit is contained within the pipe. 
     In at least one embodiment, at least a portion of the power source may be located outside of the well and at least a portion of the pipe may be contained within the well. 
     In at least one embodiment, the first frequency may be between about 0 Hz and about 1000 Hz and the second frequency is between about 10 kHz and about 100 MHz. 
     In at least one embodiment, the pipe may comprise at least two pipe modules joined together to form the pipe; and each of the at least two pipe modules may comprise at least one impulse generator unit. 
     In at least one embodiment, the frequency conversion unit may comprise a switch operable to control the energy coupling unit; a driver circuit operable to drive state transitions of the switch; and a bypass capacitor. 
     In at least one embodiment, the apparatus may comprise at least one cladding material between the pipe and the at least one energy coupling unit. 
     In at least one embodiment, the return path for the conducting cable to the power source may be selected from the pipe, the first end of the pipe being operatively coupled to the power source and the second end of the pipe being operatively coupled to the conducting cable; the reservoir, the reservoir being operatively coupled to the conducting cable and the power source; and a secondary return cable, the secondary return cable being operatively coupled to the conducting cable and the reservoir. 
     In at least one embodiment, the apparatus may comprise a controller configured to adjust at least one operational parameter of the at least one impulse generator unit. 
     In at least one embodiment, the at least one operational parameter may comprise at least one of an enable parameter, a disable parameter, a phase, a phase delay, the second frequency, a power level, and a pulse shape. 
     In at least one embodiment, the apparatus may also comprise at least one sensor, operable to generate a sensor output data, the sensor output data being used to adjust the at least one operational parameter of the at least one impulse generator unit. 
     In at least one embodiment, the sensor output data may comprise at least one of a temperature, a pressure, a voltage, a current, a status, an impedance, permittivity, an electromagnetic field, a magnetic field and an electric field. 
     In at least one embodiment, the apparatus may also comprise a controller, operable to receive the sensor output data and to adjust the at least one operational parameter of the at least one impulse generator unit, based on the sensor output data. 
     In at least one embodiment, the apparatus may also comprise at least one communication unit associated with the at least one impulse generator unit, the at least one communication unit is configured to receive the sensor output data and to transmit the sensor output data to the controller. 
     In at least one embodiment, at least one communication unit may be operatively coupled to the conducting cable; and the controller may be operatively coupled to the conducting cable and may be operable to communicate with the at least one communication unit using the conducting cable. 
     In at least one embodiment, the apparatus may comprise at least two impulse generator units; and a controller operable to independently set at least one operational parameter of each of the at least two impulse generator units. 
     In a second aspect, there is a method for enhancing the extraction of hydrocarbons from an underground reservoir using a well. In at least one embodiment, the method may include supplying periodic electrical power at a first frequency to at least one impulse generator unit; converting the supplied periodic electrical power at the first frequency to a periodic electrical power at a second frequency, the second frequency being at least ten times higher that of the first frequency, using the at least one impulse generator unit; and coupling electromagnetic energy generated by the periodic electrical power at the second frequency into the reservoir, using the at least one impulse generator unit. 
     In at least one embodiment, the method may also include setting at least one operational parameter of the at least one impulse generator unit using a controller. 
     In at least one embodiment, at least one operational parameter may comprise at least one of an enable parameter, a disable parameter, a phase, a phase delay, the second frequency, a power level, and a pulse shape. 
     In at least one embodiment, the method may also comprise measuring a sensor data. In at least one embodiment, the method may also comprise setting at least one operational parameter of the at least one impulse generator unit based on the sensor data. 
     In at least one embodiment, the sensor data may comprise at least one of a resistance, a temperature, a pressure, a voltage, a current, a status, an impedance, an electric field, a magnetic field and an electromagnetic field. 
     In at least one embodiment, the method may also include transmitting sensor data from at least one sensor; receiving the sensor data; and setting the operational parameters of the at least one impulse generator unit based on the received sensor data. 
     In at least one embodiment, the method may also include measuring a sensor data, the sensor data comprising at least one of a resistance, a temperature, a pressure, a voltage, a current, a status, an impedance, an electric field, a magnetic field and an electromagnetic field; determining at least one of at least one complex dielectric property of the reservoir and at least one propagation property of the electromagnetic field in the reservoir, based on the measured sensor data; and adjusting at least one operational parameter of the at least one impulse generator unit based on the at least one of the at least one dielectric property of the reservoir and the at least one propagation property of the electromagnetic field in the reservoir. 
     In at least one embodiment, the method may also include independently setting at least one operational parameter of at least two impulse generator units. 
     In at least one embodiment, the method may also include independently setting at least one operational parameter of the at least two impulse generator units such that the electromagnetic energy generated by the periodic electrical power from the at least two impulse generator units is spatially synchronized. 
     In another aspect, an apparatus for enhancing the extraction of hydrocarbons from an underground reservoir using a well is provided. In at least one embodiment, the apparatus may include a power source operable to supply periodic electrical power; at least two impulse generator units operable to couple electromagnetic energy generated by the periodic electrical power at a radio frequency into the reservoir; and a conducting cable being operatively coupled between the power source and the at least one impulse generator unit. 
     In at least one embodiment, the apparatus may also include a controller operable to independently adjust at least one operational parameter of each of the at least two impulse generator units. 
     In at least one embodiment, the apparatus may also include at least one sensor, operable to generate a sensor output, the sensor output being used to independently adjust the at least one operational parameter of the at least two impulse generator units. 
     In at least one embodiment, the at least one operational parameter of each of the at least two impulse generator units is adjusted such that the electromagnetic energy generated by the periodic electrical power and coupled into the reservoir from the at least two impulse generator units is spatially synchronized. 
     In at least one embodiment, the at least one operational parameter comprises at least one of a power level, a phase and a phase delay of the periodic electrical power at the radio frequency. 
     In another aspect, there is a method for enhancing the extraction of hydrocarbons from an underground reservoir using a well. In at least one embodiment, the method may also include supplying periodic electrical power to at least two impulse generator units; coupling electromagnetic energy generated by the periodic electrical power at a radio frequency into the reservoir, using at least one impulse generator unit; independently adjusting at least one operational parameter of each of the at least two impulse generator units. 
     In at least one embodiment, the method may also include measuring a sensor data; independently adjusting the at least one operational parameter of each of the at least two impulse generator units based on the sensor data. 
     In at least one embodiment, the at least one operational parameter comprises at least one of a power level, phase and a phase delay of the periodic electrical power at the radio frequency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings which show at least one exemplary embodiment, and in which: 
         FIG. 1  is a schematic view of an apparatus for enhancing the extraction of hydrocarbons from an underground reservoir using a well, in accordance with at least one embodiment; 
         FIG. 2  is a flowchart illustrating a method for enhancing the extraction of hydrocarbons from the underground reservoir, in accordance with at least one embodiment; 
         FIG. 3  is a schematic view of an impulse generator unit, in accordance with at least one embodiment; 
         FIG. 4A  is an illustration of a toroidal coil in a field building phase, in accordance with at least one embodiment; 
         FIG. 4B  is an illustration of a toroidal coil in a field release phase, in accordance with at least one embodiment; 
         FIG. 4C  is an illustration of a toroidal coil in a propagating field phase, in accordance with at least one embodiment; 
         FIG. 5A  is a schematic view of an impulse generator unit, in accordance with at least one embodiment; 
         FIG. 5B  is a schematic view of one segment of an impulse generator unit, in accordance with at least one embodiment; 
         FIG. 5C  is a schematic view of the coil subset units, mounted on the pipe, in accordance with at least one embodiment; 
         FIG. 6A  is a schematic view of a module, in accordance with at least one embodiment; 
         FIG. 6B  is a schematic view of an assembly of two stackable modules, in accordance with at least one embodiment; 
         FIG. 7A  is a schematic view of a vertical well apparatus for enhancing the extraction of hydrocarbons from an underground reservoir using a well, in accordance with at least one embodiment; 
         FIG. 7B  is a schematic view of a horizontal well apparatus for enhancing the extraction of hydrocarbons from an underground reservoir using a well, in accordance with at least one embodiment; 
         FIG. 8  is a schematic view of a pipe and coils, in accordance with at least one embodiment; 
         FIG. 9  is a schematic view of an impulse generator unit with a sensor, in accordance with at least one embodiment; 
         FIG. 10  is a schematic view of an impulse generator unit with a sensor, in accordance with at least one embodiment; 
         FIG. 11A  is a schematic view of an apparatus for enhancing the extraction of hydrocarbons with a controller and a communication unit, in accordance with at least one embodiment; 
         FIG. 11B  is an illustration of an example of a power signal with characteristic data encoded within it, in accordance with at least one embodiment; 
         FIG. 12  is a travelling wave amplifier equivalent for the implementation scheme of building of the pseudo-transverse electric and magnetic mode (TEM) in the apparatus for enhancing the extraction of hydrocarbons from an underground reservoir using a well, in accordance with at least one embodiment; 
         FIG. 13A  is a schematic view of a coupling tap, in accordance with at least one embodiment; 
         FIG. 13B  is an implementation scheme of the down-hole RF heater, in accordance with at least one embodiment. 
     
    
    
     The skilled person in the art will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the applicants&#39; teachings in anyway. Also, it will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION 
     Numerous embodiments are described in this application, and are presented for illustrative purposes only. The described embodiments are not intended to be limiting in any sense. The invention is widely applicable to numerous embodiments, as is readily apparent from the disclosure herein. Those skilled in the art will recognize that the present invention may be practiced with modification and alteration without departing from the teachings disclosed herein. Although particular features of the present invention may be described with reference to one or more particular embodiments or figures, it should be understood that such features are not limited to usage in the one or more particular embodiments or figures with reference to which they are described. 
     The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment” mean “one or more (but not all) embodiments of the present invention(s)”, unless expressly specified otherwise. 
     The terms “including”, “comprising” and variations thereof mean “including but not limited to”, unless expressly specified otherwise. A listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a”, “an” and “the” mean “one or more”, unless expressly specified otherwise. 
     Further, although process steps, method steps, algorithms or the like may be described (in the disclosure and/or in the claims) in a sequential order, such processes, methods and algorithms may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order that is practical. Further, some steps may be performed simultaneously. 
     When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article. 
     It should be noted that terms of degree such as “substantially”, “about” and “approximately” when used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of the modified term if this deviation would not negate the meaning of the term it modifies. 
     Furthermore, the recitation of any numerical ranges by end points herein includes all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, and 5). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term “about” which means a variation up to a certain amount of the number to which reference is being made if the end result is not significantly changed. 
     In addition, as used herein, the wording “and/or” is intended to represent an inclusive-or. That is, “X and/or Y” is intended to mean X or Y or both, for example. As a further example, “X, Y, and/or Z” is intended to mean X or Y or Z or any combination thereof. 
     Furthermore, reference to radio frequency (RF) range is intended to mean frequencies between about 3 kHz and about 300 GHz. 
       FIG. 1  is a schematic illustration of apparatus  100  for enhancing the extraction of hydrocarbons from a reservoir  140 , in accordance with at least one embodiment. For example, the reservoir  140  may contain crude oil or a geologic formation containing oil, heavy oil, bitumen or other hydrocarbons. The apparatus  100  includes a power source  110 , at least one conducting cable  120 , and a down-hole RF heater  130 . The down-hole RF heater  130  includes at least one impulse generator unit  160 . 
     In at least one embodiment, each impulse generator unit  160  may include at least one frequency conversion unit  150  and at least one energy coupling unit  155 . 
     In at least one embodiment, the down-hole RF heater  130  may further include a pipe  135  and a delivery portion  125  of the conducting cable  120 . For example, the delivery portion  125  of the conducting cable  120  may be substantially contained within the pipe  135 . 
     In at least one embodiment, the down-hole RF heater  130  may be located inside the reservoir  140  below a ground surface  145 . As shown in the example embodiment in  FIG. 1 , a well  147  may extend from the ground surface level  145  into the reservoir  140 . For example, the well  147  may contain a well portion of the conducting cable  120 . 
     In order to enhance the extraction of hydrocarbons from the reservoir  140  using the RF heating technique, the down-hole RF heater  130  of apparatus  100  radiates an electromagnetic field into the reservoir  140 . The down-hole RF heater  130  is a device that sets up an electromagnetic field in the medium. In at least one embodiment, the down-hole RF heater  130  may operate as a distributed antenna. In at least one another embodiment, the down-hole RF heater  130  may operate as a lossy transmission line. The radiated electromagnetic field has a fundamental frequency within the radio-frequency range. For example, the fundamental frequency may be approximately about 10 kHz to about 100 MHz. The radiated signal at this fundamental frequency may be further modulated or may have a form of a train of pulses. 
     As it is shown in  FIG. 1  the conducting cable  120  may carry the electrical energy from the above ground equipment  110  to the down-hole RF heater  130 . Typically the electrical energy generated by the power source  110  is in the form of a waveform that is approximately sinusoidal and periodic, with a repetition rate denoted as a first frequency. This first frequency is not necessarily constant with time and may vary over a range of frequencies. Furthermore, this signal may deviate significantly from sinusoidal time dependence. 
     It should be borne in mind that at frequencies higher than 500 Hz, the electromagnetic field may magnetically couple to the pipe  135 , resulting in excessive power losses. To prevent excess energy loss in the conducting cable, the first frequency may be low relative to the eventual radiated frequency (i.e. frequency of the energy radiated from the down-hole RF heater  130 ), in at least one embodiment. 
     In at least one non-limiting embodiment, the first frequency falls within a range from about 0 Hz to about 1000 Hz. 
     In at least one non-limiting embodiment, the first frequency may fall within a range from about 0 Hz to about 500 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 0 Hz to about 100 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 0 Hz to about 60 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 0 Hz to about 50 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 0 Hz to about 40 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 0 Hz to about 30 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 0 Hz to about 10 Hz. 
     In at least one non-limiting embodiment, the first frequency may fall within a range from about 30 Hz to about 1000 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 40 Hz to about 1000 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 50 Hz to about 1000 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 60 Hz to about 1000 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 70 Hz to about 1000 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 80 Hz to about 1000 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 100 Hz to about 1000 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 200 Hz to about 1000 Hz. 
     In at least one non-limiting embodiment, the first frequency may fall within a range from about 30 Hz to about 800 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 40 Hz to about 500 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 50 Hz to about 300 Hz. In at least one non-limiting embodiment, the first frequency may fall within a range from about 30 Hz to about 100 Hz. 
     In the down-hole RF heater  130 , the electrical power signal at the first frequency is modulated such that the spectrum is shifted to a much higher frequency which will be referred to as the second frequency. The second frequency may be selected for efficient radiation from the down-hole RF heater  130 . 
     In at least one embodiment, the second frequency signal emanating from the down-hole RF heater  130  may be approximately sinusoidal. The second frequency signal may also deviate significantly from the sinusoidal time dependence. For example, the second frequency signal may also be approximately periodic. As such the second frequency may vary with time. 
     Hence when referring herein to the first frequency signal and the second frequency signal as being periodic, it is implied that the repetition rates of the first frequency signal and the second frequency signal are approximately constant over short time epochs. It is also implied that the first frequency and the second frequency signals may vary with time in a deterministic or random fashion. 
     The second frequency may also be different at different impulse generator units  160  or at different groups of impulse generator units  160 . 
     In at least one exemplary embodiment, the power source  110  supplies periodic electrical power having a periodic waveform at a low first frequency. This electrical power is delivered via the conducting cable  120  to the underground down-hole RF heater  130 . 
     Further, the down-hole RF heater  130  receives the periodic electrical power at the first frequency and converts (modulates) the received periodic electrical power to a significantly higher second frequency. The periodic electrical power at this significantly higher second frequency then generates an electromagnetic field that is radiated into the reservoir  140  in order to enhance the extraction of hydrocarbons from the reservoir  140 . This process may be also described as “coupling of the electromagnetic energy generated by the periodic electrical power into the reservoir  140 ”. 
     In at least one non-limiting embodiment, the second frequency may be radio frequency. In at least one non-limiting embodiment, the second frequency falls within a range from about 10 kHz to about 100 MHz. In at least one non-limiting embodiment, the second frequency may fall within a range from about 30 kHz to about 50 MHz. In at least one non-limiting embodiment, the second frequency may fall within a range from about 50 kHz to about 10 MHz. In at least one non-limiting embodiment, the second frequency may fall within a range from about 100 kHz to about 10 MHz. 
     The second frequency of the radiated energy may further be optimized in order to provide a higher amount of heat at a particular distance from the RF heater  130  (e.g. several meters to tens of meters where heat is desired), and to provide a lower amount of heat produced in close proximity to the RF heater  130  (where heat is undesirable), or otherwise engineered to deliver required heating pattern within the reservoir. 
     In at least one embodiment, the power source  110  may be any constant current power source capable of supplying periodic electrical power of approximately several kilowatts (kW) to several megawatts (MW) and where the supplied electromagnetic field waveform is modulated at a first frequency. For example, the power source  110  may supply a current which may fall within the range of about 10 Amperes (A) to about 1000 A. For example, the power source  110  may supply a voltage which may fall within the range of about 100 Volts to about 20 kilovolts (kV). For example, for the apparatus  100  where the pipe  135  has a length that is typically more than 200 m, the power source  110  may supply a current of approximately 300 A and a voltage of approximately several kV. 
     In at least one embodiment, the power source  110  may be located at least partially above the ground surface level  145  and at least partially outside of the well  147 . 
     In at least one embodiment, the conducting cable  120  conducts current from the power source  110  to the down-hole RF heater  130 . It should be understood that the conducting cable  120  may be made of any material suited for transmission of electrical power signal. For example, the conducting cable  120  may be made of copper, aluminium, or any highly conductive metal of low electrical conduction losses. For example, the conducting cable  120  may also be made of a standard underground power cable. 
     Referring still to  FIG. 1 , the pipe  135  has a first end  136  and a second end  137 . The first end  136  is downstream from the power source  110  and the second end  137  is downstream from the first end  136 . 
     A portion of the conducting cable  120 , which is located between the first end  136  of the pipe  135  and the second end  137  of the pipe  135 , is referred herein to as a hot delivery cable  125 . The hot delivery cable  125  may be substantially located inside the pipe  135  and may deliver current to at least one impulse generator unit  160 . 
     In at least one embodiment, the pipe  135  may be used as a return path for the delivery cable  120  to the source  110 . In this example embodiment, the delivery cable  125  may enter the pipe  135  at the first end  136  of the pipe  135  and the delivery cable  125  may be shorted to a casing of the pipe  135  at the second end  137  of the pipe  135 . In this example embodiment, the pipe  135  may be operatively coupled to the power source  110  via a return cable  123 . 
     In another embodiment, the surroundings of the pipe  135 , or reservoir  140 , may be used as a return path for the delivery cable  120  to the power source  110 . In this example, the power source  110  may be operatively coupled to conducting cable  120  and to the reservoir  140 . The delivery cable  125  may be then operatively coupled to the conducting cable  120  and to the reservoir  140 . Thus the reservoir  140  may become coupled to the conducting cable and the power source  110 . 
     In another embodiment, a secondary cable (not shown in  FIG. 1 ) may provide the return path for the conducting cable  120  to the power source  110 . In this example embodiment, the power source  110  may be first operatively coupled to a first end of the conducting cable  120 . The second end of the conducting cable  120  then may be operatively coupled to the first end of the secondary return cable. The second end of the secondary return cable may then be coupled to the power source  110 . 
     The pipe  135  may be made of any conducting material, for example, steel. One of the advantages of the invention is that the pipe  135  may be any standard pipe used in oil and gas industry. For example, a diameter of the pipe  135  may be between 3 and 9 inches or more. Wider or narrower diameters may be used, depending on the specifics of the oil well and oil formation and other factors such as economics. 
     The length of the pipe  135  and the length of the hot delivery cable  125  may be approximately the same and may be as long as the length of the formation reservoir  140 . For example, the length of the pipe  135  may be approximately 100 to 2000 meters long. 
     In at least one embodiment, the pipe  135  may be built of contiguous sections. 
     In at least one embodiment, additional tubes may be contained in the pipe  135 . For example, the tubes may carry water or gas or solvents required by the process. In particular, liquids or pressurized gases might be used for cooling purposes, or as additional driving medium for hydrocarbon production. 
     In at least one embodiment, at least one impulse generator unit  160  is located partially inside the pipe  135 . For example, at least one portion of the frequency conversion unit  150  may be located inside the pipe  135  and at least one portion of the energy coupling unit  155  may be located outside of the pipe  135 . In at least one embodiment, at least two impulse generator units  160  are located along the pipe  135 . 
     For example, if the length of the pipe  135  is approximately 1000 meters, there may be 4000 impulse generator units  160  (for example, one every 25 cm), distributed along the pipe  135  or more. The actual number of impulse generator units  160  depends on the specific formation and heating requirements, as well as the specifics and power output of impulse generator units  160 . The power output and other characteristics of the impulse generator units  160  may vary in different implementations, for example, depending on the specific transistor or other active elements used. 
     Referring still to  FIG. 1 , in at least one embodiment, the frequency conversion unit  150  may be configured to receive periodic electrical power having a periodic waveform at a first frequency. As discussed above, the first frequency may be relatively low and for example may fall in the range of about 0 Hz and about 1000 Hz. 
     The frequency conversion unit  150  may then convert the periodic electrical power having a first frequency to periodic electrical power having a second frequency. In at least one embodiment, the second frequency may be at least 10 times that of the first frequency. 
     In at least one embodiment, the second frequency is radio frequency (RF). For example, the second frequency may fall in the range of about 10 kHz and about 100 MHz. 
     The frequency conversion unit  150  may transmit periodic electrical power having a periodic waveform at the second frequency to the energy coupling unit  155 . The energy coupling unit  155  may then couple electromagnetic energy into the formation reservoir  140 . 
     For example, the energy coupling unit  155  may be a strip, a wire, a strip or wire circuit, a section of a pipe, a coil or coil winding placed on the outside of the pipe and connected to impulse generator unit  160 . For example, coil winding may be made of highly conductive wire such as copper or aluminum wound on a dielectric form. 
     In at least one embodiment, the apparatus  100  may also include a controller  105 . For example, the controller  105  may be operably connected to the power source  110 . The controller  105  may be configured to determine at least one operational parameter of the at least one impulse generator unit  160 . The controller  105  may further send this at least one operational parameter to the at least one impulse generator unit  160 . 
     Further, if the apparatus  100  comprises at least two impulse generator units  160 , the controller  105  may be configured to independently determine, set, or adjust the operational parameters of each of the impulse generator units  160 . For example, the operational parameters may comprise at least one of an enable parameter, a disable parameter, a phase, a phase delay, a frequency (for example, the second frequency), a power level, and a pulse shape. 
     In at least one embodiment, an impulse generator unit  160  may contain at least one communication/controller unit  170 . For example, the communication/controller unit  170  may receive the operational parameters from the controller  105 . The communication/controller unit  170  may also control the operation of the other components of the impulse generator unit  160 . For example, the communication/controller unit  170  may control the operation of the other components of the impulse generator unit  160  independently from the controller  105 . For example, the communication/controller unit  170  may control the operation of the frequency conversion unit  150  and/or the energy coupling unit  155 . 
     The communication/controller unit  170  may also be either a communication unit or a controller unit or both. For example, the communication/controller unit  170  may operate independently from the controller  105 . 
     In at least one embodiment, one communication/controller unit  170  may receive the operational parameters from the controller  105  and/or control the operation of two or more impulse generator units  160 . 
     Referring now to  FIG. 2 , shown therein is a flowchart of an example embodiment of the method  200  for enhancing the extraction of hydrocarbons from an underground reservoir. At  210 , periodic electrical power is provided having a periodic waveform at a first frequency. The current or power may be generated above the ground surface level  145 . The periodic electrical power could either be a direct current (DC) or a low frequency alternating current (AC). 
     In at least one embodiment, the generated periodic electrical power is characterised by a low-frequency periodic signal at the first frequency. For example, the current may be delivered to the power source  110  via high-voltage transmission lines or generated/reformed locally on the surface. 
     At  220 , the periodic electrical power signal at the first frequency is conducted to at least one frequency conversion unit  150 . For example, practical electrical power generation from a diesel generator may result in a sinusoidal waveform. In another example, the periodic electrical power signal at the first frequency may also be sourced from power invertors, such that the waveform shape can deviate significantly from sinusoidal. 
     At  230 , the supplied periodic electrical power having a waveform modulated at the first frequency is converted to periodic electrical power having a waveform modulated at a second frequency. In at least one embodiment, the conversion may be performed by modulation (for example, on/off) of the delivered power at the second frequency. 
     In at least one embodiment, the second frequency is at least ten times that of the first frequency. In at least one embodiment, the second frequency is a radio-frequency signal having spectral power content in the range from about 10 kHz to about 100 MHz. 
     At  240 , the electromagnetic energy, generated by the periodic electrical power with the waveform modulated at the second frequency, is coupled into the reservoir  140 . In at least one embodiment, the electromagnetic energy is radiated from at least one energy coupling unit  155  into the reservoir  140 . 
     Referring now to  FIG. 3 , a schematic of an example embodiment of an impulse generator unit  360  is illustrated which includes a frequency conversion unit  350  and an energy coupling unit  355 , in accordance with at least one embodiment. This frequency conversion unit  350  comprises a toroidal transformer  354 , a capacitance  358 , a switch  362 , and a switching/modulation driver circuit  364 . The energy coupling unit  355  is implemented by a coil  355 , positioned at least partially outside the pipe  135  (shown in  FIG. 1 ). 
     In the example embodiment, the periodic electrical power, discussed above, is delivered to a portion of the delivery cable  325 . 
     In at least one embodiment, the power delivered via the delivery cable may be AC power. In at least one embodiment, the waveform of the power delivered may be sinusoidal. In another embodiment, the power waveform may have any periodic form other than sinusoidal. As discussed above, the power waveform may be modulated at the first frequency. 
     In at least one embodiment, a toroidal transformer  354  may be coupled to or may surround the portion  325  of the delivery cable  125 . The toroidal transformer  354  couples the periodic electrical power to an electrical circuit, which contains a coil  355 , a switch  362 , and a capacitor  358 . A person skilled in the art will appreciate that the toroidal transformer  354  is capable to couple the periodic electrical power to the load from the delivery cable portion  325 . The Thévenin&#39;s equivalent source voltage and impedance are functions of the current passing through the delivery cable portion  325  and the parameters of the coupling toroid  354 . In at least one embodiment, the parameters of toroids  354  may be identical or almost identical. 
     In at least one embodiment, the current delivered to the cable delivery portion  325  does not vary with the location of the toroidal transformers  354  along the delivery cable  125  on  FIG. 1 . Moreover, the current delivered to different portions of the delivery cable  125  may be approximately the same. For example, the current delivered to an end portion  126  ( FIG. 1 ) may be approximately the same as the current delivered to an end portion  127  ( FIG. 1 ). Therefore, the toroidal transformers  354 , located at different positions along the delivery cable  125 , may receive approximately the same amount of current, or may have the same amount of power available to them, and therefore the same AC power may be coupled to each frequency modulation unit  150 . 
     Referring again to  FIG. 3 , in at least one embodiment, the capacitor  358  may provide an RF bypass. The capacitor  358  does not need to have a significant capacitance because the AC frequency is typically around several 100 Hz or less. However, without the capacitor  358 , the current would couple back into the AC line and the high inductance of the power coupling toroid  354  would limit the rate of current rise through the radiating coil  355 . 
     In at least one embodiment, each impulse generator unit  360  may have a rectifier to convert AC power to DC power. 
     In at least one embodiment, the switch SW  362  may be driven at the second frequency by a signal from the modulation drive circuit  364 . In at least one embodiment the signal can have approximately a form of a square wave. In at least one exemplary embodiment, the second frequency may be in the RF range. For efficiency, it is important for the modulation of the switch SW  362  to be sufficient to turn the switch completely on or off with minimal transition time. 
     As soon as the current rise slows down, the switch SW  362  should be opened again. This collapses the current through the coil  355  and generates an electromagnetic wave pulse. 
     In at least one embodiment, the switch  362  may be a high power switching device which facilitates the AC to RF conversion. For example, the switch  362  may be a high power semiconductor switch. For example, the switch may be a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar junction transistor, or other semiconductor device. 
     When the switch closes, current in the coil  355  builds up at a rate proportional to the instantaneous AC voltage. The AC power from the AC delivery cable is converted to a high frequency modulation current at the coil  355 . 
     The radiation mechanism of the coil  355  may comprise three phases, explained in  FIGS. 4A, 4B, and 4C . 
     Referring now to  FIG. 4A , illustrated therein is a toroidal coil  455  in a field building phase, according to at least one embodiment. The coil  455  begirds or encircles a portion of the steel pipe  435 . At the field building phase, coil current I coil  generates a magnetic field H ϕ , which encircles the pipe  435 . During this phase, the pipe&#39;s induced current is 0. The total stored field energy of the coil at the end of this phase is 
               E   =       1   2     ⁢     L   coil     ⁢     I   coil   2         ,         
where L coil  is the inductance of the coil  455 .
 
     Referring now to  FIG. 4B , illustrated therein is the toroidal coil  455  in a field release phase, according to at least one embodiment. At the field release phase, the coil current quickly decreases to zero, which makes the coil almost transparent to magnetic fields. The collapsing magnetic field sets up two events. First, a brief burst of induced current, denoted as J ind , flows in the outside cladding region of the pipe along the z axis. Second, a portion of the magnetic field gives rise to an electric field and the combined EM field results in an outgoing radiation burst. 
     Referring now to  FIG. 4C , illustrated therein is the toroidal coil  455  in a propagating field phase, according to at least one embodiment. At the propagating field phase, the emanating EM field propagates outward like an expanding toroid of a short energy burst. The electric field contained in the expanding toroidal volume interacts with the medium resulting in dissipation that is converted into heat. 
     The parameters and the operating conditions of the switch  362  may be estimated approximately from the desired energy to be coupled to the reservoir  140  and the cycle of the energy coupling phases. 
     For example, if the cycle of three energy coupling phases described above is repeated every 100 nanoseconds or 10 7  Hz, in order to couple the energy of 200 W (which corresponds to 200 Joules per second) to the reservoir  140 , the coil energy after each build up phase should be: 200 W/10 7  Hz=20 μJ. This means that each emanating burst may generate 20 μJ. If the inductance of the coil  355  is L coil =0.5 μH, the estimate of the coil current from the equation 
             E   =       1   2     ⁢     L   coil     ⁢     I   coil   2             
gives 13 A. To achieve this reasonable current, the switch input voltage should be approximately 30 V, if estimated using the equation
 
     
       
         
           
             
               V 
               coil 
             
             = 
             
               
                 L 
                 coil 
               
               ⁢ 
               
                 
                   
                     dI 
                     coil 
                   
                   dt 
                 
                 . 
               
             
           
         
       
     
     Referring now to  FIG. 5A , shown therein is a schematic view of an impulse generator unit  560 A, according to at least one embodiment. In this example, a coil subset unit  555  is powered by a frequency conversion unit  550 . A coil subset unit  555  may comprise more than one coil  558 . 
     Referring now to  FIG. 5B , shown therein is a schematic view of one segment of an impulse generator unit  560 B, according to at least one embodiment. 
     In at least one embodiment, the pipe  535  may be covered by cladding  539  and form a layer between the pipe  535  and the coils  555 . For example, a cladding may be a thin sheet made of a highly conductive material, which has very low magnetic permeability. For example, the cladding may be made of copper or aluminum. The cladding may also be a foil type wrapping that is easily applied in the pipe fabrication process or a tube/pipe otherwise fixed on the pipe  535 . The cladding allows for efficient propagation of the EM energy away from the pipe. Therefore, the cladding may help to increase the ratio of desired heat to undesired heat. 
     The cladding  539  may also include a dielectric material and a ceramic material. 
     Referring now to  FIG. 5C , shown therein is a schematic view of the coil subset units  555 , mounted on the pipe  535 , according to at least one embodiment. 
     In at least one embodiment, conversion of periodic electrical power at the first frequency to periodic electrical power at the second frequency is distributed along the pipe. For example, an array or a plurality of the frequency conversion units  150  may be located along the pipe  135 . In at least one embodiment, the frequency conversion units  150  are separated by approximately equal distance. 
     With a plurality of the impulse generator units along the pipe, there will be a plurality of points of conversion of electrical power at the first frequency to RF power, which is modulated at the second frequency. As the active AC to RF conversion relies on vulnerable electronics, such a configuration allows for the avoidance of a single point of failure within the apparatus. 
     The density of the impulse generator units  160  along the length of the pipe  135  may be adjusted depending on the requirements and environmental conditions. In one of the embodiments, each frequency conversion unit  150  may draw approximately 200 W from the AC source. For example, approximately 10,000 energy coupling units may be required over the pipe length of about one to two kilometers, resulting in a total power draw of approximately 2 MW from the power source  110 . 
     Referring now to  FIG. 6A , shown therein is a cross-section of an exemplary embodiment of a module  600 A which may be assembled with other modules to form a complete pipe  135  assembly. A pipe portion  635 , conducting cable  625 , frequency conversion units  650 , energy coupling units  655 , and the cladding  639  have been previously described. The module  600 A may contain at least one frequency conversion unit  650  and at least one energy coupling unit  655 . 
     In at least some embodiments, the apparatus  100  may comprise a plurality of stackable modules  600 A, as shown in  FIG. 6B . For example, connectors  695  may connect the modules to each other. In at least one embodiment, the connectors may be blind mate connectors. 
     For example, the length of one module  600 A may be approximately 10 meters. 
     While the apparatus  100  may be built over a contiguous pipe and such that construction may be mechanically robust, the coils  655  are vulnerable during the installation phase. Therefore, in at least one embodiment, dielectric fillers or spacers  651  may be used between the coils  655 . In at least one embodiment, a sacrificial dielectric layer  653  may coat the entire cladding with coils  655 . This dielectric layer  653  then may be scraped off when the apparatus is installed down-hole or it may be destroyed during the heating process. 
     The side portions  690  and  693  of the modules  600 A may have various configurations. For example, the side portions  690  and  693  of the modules  600 A may be adapted to ease connection between the modules. For example, the side portions  690  and  693  of the modules  600 A may have larger diameter than the central portion of the modules  600 A. In at least one embodiment, the pipe  635  may have slightly smaller diameter in between the side portions  690  and  693  of the modules  600 A, thus creating a space to safely place coils  655 , spacers  651 , and sacrificial dielectric layers  653 . 
     Constructing a pipe  135  from stackable modules  600 A has numerous advantages. Modules  600 A may be cost effective to manufacture, install, operate and eventually dismantle. In at least one embodiment, the modules  600 A are identical and may be easily manufactured. For example, if one of the units fails, only the module that contains the failed unit needs to be replaced. This may provide easy and cost-effective repairs of the assembly. 
     In at least one embodiment, any number of modules  600 A may be coupled and connected to form a pipe  135 . Therefore, pipes  135  of any length may be built. 
     In at least one embodiment, the modules may have at least one conduit  697 . For example, the conduit  697  may be a nonconductive pipe that is housed inside the module  600 . The conduit  697  may be designed and/or constructed in such a way that, upon connection of several modules, it creates a non-conductive conduit extending through all modules. For example, the frequency conversion units  650  and other hardware may be mounted on the conduit  697 . This may facilitate fabrication of the module  600 . 
     For example, once all the modules are deployed, the conduit  697  may facilitate insertion of the hot cable  625 , which may be fed through the conduit  697 . In another embodiment, cable  125  may be pre-inserted into the modules and connection may be established at module interfaces to form the conducting power cable  125 . 
     Generally, a formation layer with the crude oil may have around a few to a few hundred meters in height. The length and the width of the reservoir with the crude oil may stretch for several kilometers. 
       FIG. 7A  illustrates a vertical well apparatus  700 A for enhancing the extraction of hydrocarbons, according to one of the embodiments. In this apparatus, a down-hole RF heater  730 A is located inside a reservoir  740 A and is oriented vertically. The vertical RF heater  730 A does not need to be longer (higher) than the height of the reservoir  740 A. For example, the length of the RF heater  730 A may be approximately 200 meters. However, to efficiently extract hydrocarbons from the wide and long reservoir  740 A, more than one vertical well apparatuses  700 A should be built. 
       FIG. 7B  illustrates a horizontal well apparatus  700 B for enhancing the extraction of hydrocarbons, according to one of the embodiments. In this exemplary embodiment, the down-hole RF heater  730 B is located horizontally inside the reservoir  740 B. 
     Using modules  600 A to construct the heaters  730 A and  740 B, the length of the heaters  730 A and  740 B may be adjusted to the length or the height of the formation reservoirs  740 A or  740 B. Therefore, by adjusting the number of modules  600 A and their operational parameters, both horizontal and vertical assemblies may be built using the same modules  600 A. 
     In at least one embodiment, sensors may be placed inside and/or outside of the pipe  135  to monitor various environmental aspects. For example, the apparatus  100  may include at least one sensor to detect and/or measure a sensor data. The sensor data may comprise at least one of a temperature, a pressure, a voltage, a current, a status, impedance, a resistance, permittivity, an electromagnetic field, a magnetic field and an electric field. In at least one embodiment, at least one sensor may be at least one of a temperature sensor, a pressure sensor, and a status sensor. In at least one embodiment, at least one sensor may detect and measure a voltage or a current, related to the energy coupling unit  155 . 
     In at least one embodiment, the apparatus  100  may record and/or process the sensor data. In at least one embodiment, the output sensor data may be used to set and/or adjust the operational parameters of the at least one impulse generator unit  160 . For example, one may want to enable or disable one particular impulse generator unit or an array of impulse generator units. For example, a phase, a phase delay, a frequency (for example, the second frequency), a power level, and a pulse shape of the power may be adjusted based on the received data from the sensors. 
     Those skilled in the art will understand that for harmonic (sinusoidal) signals the terms phase delay and time delay are equivalent. When the signal is a periodic train of pulses and, hence, in the spectral domain, is represented by a fundamental harmonic component (with frequency equal to that of the periodic frequency) and many higher order harmonics, the term “phase delay” becomes less precisely defined. In the context of this application, for a train of periodic pulses at the second frequency, the phase delay shall describe the phase delay of the fundamental harmonic (at the second frequency). This phase delay is equivalent to the time delay introduced to the train of pulses. 
     The output sensor data may be then transmitted to a controller  105 . The controller  105  may be configured to determine at least one operational parameter of at least one impulse generator unit based on the sensor output data. The controller  105  may then send the at least one operational parameter to the at least one impulse generator unit. For example, the at least one operational parameter may comprise at least one of an enable parameter, a disable parameter, a phase, a phase delay, a frequency (for example, the second frequency), a power level, and a pulse shape. 
     For example, if the apparatus  100  comprises at least two impulse generator units  160 , the controller  105  may independently adjust the operational parameters of each of the impulse generator units  160  based on the sensor data received from the sensors. 
     In at least one embodiment, the sensor associated with one impulse generator unit  160  may be able to measure the electromagnetic field. For example, the electromagnetic field may be generated by the same impulse generator unit  160 , by another impulse generator unit, by impulse generator units within the same module, or by any other array of the impulse generator units. 
     Referring now to  FIG. 8 , wherein illustrated are energy coupling units  855 A,  855 B,  855 C,  855 D,  855 E,  855 F, and a pipe  835 , according to at least one embodiment. In this example embodiment, the energy coupling unit  855 D radiates the EM field into the reservoir  140  and the other energy coupling units  855 A,  855 B,  855 C,  855 E, and  855 F are listening and measuring the EM field. 
     For example, there may be n energy coupling units  855 . In this example embodiment, the energy coupling unit  855 F may be the n-th energy coupling unit. For example, when the energy coupling unit  855 D radiates the EM field into the reservoir  140 , the other (n−1) energy coupling units may measure the EM field. 
     In at least one embodiment, the apparatus  100  may record and/or process the EM field data. Based on the measured radiated and received EM field, the coupling between the energy coupling units  855  may be determined. For example, the coupling of the energy between the energy coupling units  855  may be a function of dielectric parameters of the medium. For example, these measurements may provide the data for the tomographic computation of the medium dielectric properties along z. 
     For example, the electromagnetic propagation constant in the reservoir  140  and/or any other dielectric property of the reservoir  140  may be estimated and/or determined based on the sensor data. For example, complex dielectric property of the reservoir  140  may be estimated and/or determined. For example, conductivity property of the reservoir  140  may be estimated and/or determined. For example, at least one propagation property of the electromagnetic field in the reservoir  140  may be estimated and/or determined based on the sensor data. For example, the electromagnetic propagation constant in the reservoir  140  and/or any other dielectric property of the reservoir  140  may be determined based on the measured transmitted and received EM field. At least one operational parameter of the at least one impulse generator unit  160  may be adjusted based on the determined dielectric property of the reservoir  140  and/or the propagation property of the electromagnetic field in the reservoir  140 . 
     In at least one embodiment, the dielectric properties of the medium or phase velocity of electromagnetic waves in the medium may be estimated by measurements made at the location close to one impulse generator unit, while another impulse generator unit radiates. These measurements may further provide information regarding the health of the coil  155  and the impulse generator unit  160 . 
     The measurement of the energy coupling may be very short, requiring only several seconds to complete. In at least one embodiment, sets of coils may radiate simultaneously, which may speed up the monitoring process. For example, such tomography algorithm can be run every few hours of operation of the apparatus in order to update the reservoir model and track changes. 
     In at least one embodiment, the tomography algorithm may be used along with the apparatus temperature measurements and surface seismic analysis. 
     Referring now to  FIG. 9 , shown therein is an impulse generator unit  900  with a coil sensor, according to at least one embodiment. A capacitor  915 , a coil  955 , and a switch  962  have been previously described. In at least one embodiment, a small series resistor  973  is located between the coil  955  and the switch  962  to measure voltage V A -V B . In this example, the resistor  973  determines the coil current, when the switch  962  is closed during the field building phase. 
     In at least one embodiment, measurement of the voltage V C -V B , when the switch  962  is opened, provides the open circuit voltage. In this example, the radiated energy from the coil can be estimated during the field building phase. 
     In at least one embodiment, the open circuit voltage measurement can be used to determine the magnetic field that propagates from one coil to the next. 
     Referring now to  FIG. 10 , illustrated therein is an example embodiment of an impulse generator unit  1000  with a coil sensor. The delivery cable  1025 , the toroid  1002 , the capacitor  1015 , the coil  1055  have been previously described. In this example, the AC/DC converter  1065  generates a regulated DC power supply voltage V AC/DC  that is used to power the driver electronics as well as a computational block of a radiated power estimator  1070 . V A  is the voltage developed across a small resistor  1076 , R 1 , that is proportional to coil current. V B  is the voltage at node  1074 . 
     The driver block  1045  determines when to turn on and off the switch  1062  by analysing voltages V A  and V B , the modulating square wave, as well as control commands received from the controller  105  passed through the AC power line  1025  (via conducting cable  120 ) and coupled into an impulse generator unit  1000  via the coupler  1002 . For example, this link may be bidirectional. In at least one embodiment, the switch  1062  may be implemented by a MOSFET. 
     Referring still to  FIG. 10 , the radiated power estimator  1070  may estimate the power radiated from the coil  1055 . For example, the estimated power may be used in the overall reservoir mapping to estimate the temperature profile in the medium surrounding the down-hole RF heater  130 . 
     In at least one embodiment, the apparatus may control the down-hole RF heater  130  based on feedback from a network of sensors. Extensive control of individual components of the impulse generator units may be implemented. 
     In at least one embodiment, the output of the sensors is digitized with the digitized sample values assembled into a data packet that is further augmented with error correction coding. This output of the sensors is then periodically transmitted to the surface controller  105  via the electrical power cable  125 . 
     Referring now to  FIG. 11A , shown therein is an example embodiment of the apparatus  1100  for enhancing the extraction of the hydrocarbons using data communication units. A power source  1110 , a pipe  1135 , a delivery cable  1125 , and a toroid  1102  have been described. For example, a control communication unit  1122  may be coupled into the conducting cable  1120  with data for N frequency conversion units, used in the apparatus, where N is an integer. The conducting cable  1120  then delivers this data to the delivery cable  1125 . Inside the pipe  1135 , the communication unit  1180  may be then coupled to the toroid  1102 . 
     In at least one embodiment, a communication unit  1180  may receive data from the delivery cable  1125  and may transmit this data to a frequency conversion unit  1150 . The modem  1180  may also receive data from the at least one sensor and may transmit the data via the delivery cable to the controlling communication unit  1122 . 
     While there may be many individual communication units  1180 , which need to communicate data to the modem  1122 , the rate of communication required per each communication unit  1180  may be quite modest. For example, changes in the medium in terms of temperature and water desiccation have time constants of the order of hours. 
     In at least one embodiment, the delivery cable  1125  may be used as a communication line for the control signals sent to the individual impulse generator units  1160  from the surface by the controller  1105 . In this example, the controller  1105  may be operationally coupled to the control communication unit  1122 . 
     Referring now to  FIG. 11B , shown therein is an illustration of an example of a power signal  1101  that has characteristic data encoded within it. In this example embodiment, the power signal comprises a header  1143  and a plurality of channels, wherein a first channel  1145  and the Nth channel  1147  are shown in  FIG. 11B . For example, the header  1143  may be used for frame and clocking synchronization. 
     For example, the super frame time for all of the RF modules may be several seconds. 
     In at least one embodiment, the channel N may be a time slot of a 1 millisecond duration dedicated to the Nth impulse generator unit. The channel N may be divided into two halves for up link and down link traffic. 
     For example, the communication units  1122  and  1180  may be implemented by modems and have some protocol system. In at least one embodiment, a time division multiplex system may be used to transmit the data. 
     In at least one embodiment, modulation within the channel frame may be a robust modulation such as binary phase-shift keying (BPSK). Hence, for 10000 units the super frame duration may be of the order of 10 seconds long. A person skilled in the art will appreciate that reflections and frequency distortion may be overcome given the state of the art in the modern wireless and power line communications. 
     In at least one embodiment, the controller  1105  or the control communication unit  1110  may receive various data from the individual communication units  1180 . For example, the controller  1105  may receive the data from at least one sensor described herein. The controller may further calculate various operational parameters to be transmitted down-hole to the individual impulse generation units  1160 . 
     In at least one embodiment, the controller  1105  may also send various data to the individual communication units  1180  via the at least one control communication unit  1110 . For example, the RF modulation may be enabled or disabled and the RF phase of the modulation and transition repetition rate may be set using this type of communication. The controller  1105  may determine and may send various operational parameters to the impulse generating units  1160 . For example, a phase, a phase delay, a frequency (for example, the second frequency), a power level, and a pulse shape may be determined and transmitted to the at least one impulse generator unit  1160 . 
     The data for each individual communication unit  1160  may be encoded in one power signal  1101 , as described above. Therefore, when the apparatus comprises more than two impulse generator units  1160 , the controller  1105  may independently adjust operational parameters of each of the at least two impulse generating units  1160 , using the control communication unit  1122 . 
     In at least one embodiment, a propagation constant as a function of the axial distance along the pipe  135  may be estimated with the tomographic sensing as described above, or with information provided by other sensors described above augmented with prior knowledge of the reservoir. Knowing the propagation constant, the phases and amplitudes of each of the impulse generator units  160  in an array of impulse generator units  160  may be set up to be commensurate with the phase and amplitudes of a desired distribution of voltage or current, or more generally, electric and magnetic fields of a guided or standing wave mode along the pipe  135 . 
     For example, the amplitudes and phases of the impulse generator units  160  may be set up to establish a pseudo TEM (Transverse Electromagnetic Mode) along the pipe  135 , which may radiate electromagnetic power into the formation  140 . Referring to  FIG. 12 , the phase delay between consecutive impulse generator units  160  would be equal to the propagation constant β (which may vary with the location along the pipe) multiplied by the distance ΔZ along the pipe between adjacent impulse generator units  160  (which may also vary along the pipe  135 ). In at least one embodiment, to maintain uniform radiation, the power radiated out along the distance ΔZ may be equal to the power added by an individual impulse generator unit  160  corresponding to that location along the pipe  135 . 
     Referring now to  FIG. 13A , shown therein is an example embodiment of a coupling tap  1300 . The coupling core  1305  may be positioned around the AC hot delivery cable  1325 . In this example, there is no direct connection to the hot delivery cable that may carry approximately several thousand volts. The coupling core  1305  may be made, for example, of iron. 
     In at least one embodiment, each power tap may correspond to one impulse generator unit  160 . Sets of taps  1300  may be optionally lumped together for a more convenient design. 
     For example, the core  1305  may have a length that is long enough to sufficiently couple most of the magnetic field in a section to the secondary winding  1302 . For example, a small block of iron core may be sufficient for coupling of several hundred watts. The power of 250 W may be extracted from about 20 cm of the hot delivery cable  1325  using such inductive coupling. In at least one embodiment, the coupling cores with shorter lengths than 20 cm may be used in order to avoid single point of failure. 
     It should be noted, that if the length of the core  1305  is short, then the AC magnetic lines may partially bypass the iron core section such that only a partial field coupling occurs. A core with an optimal length may be engineered to minimize the voltage drop due to the series inductor in the AC line.  FIG. 13B  illustrates an implementation scheme of the down-hole RF heater  1301  using the coupling taps  1300 , according to at least one embodiment. In this example, secondary windings  1302  deliver power to impulse generator units  1360 . 
     A number of embodiments have been described herein. However, it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto.