WO2014189533A1

WO2014189533A1 - Apparatus and method employing microwave resonant cavity heating of hydrocarbon fluid

Info

Publication number: WO2014189533A1
Application number: PCT/US2013/059198
Authority: WO
Inventors: Tracy NEITZ; Wai-Ming Tam; Brian Oliver Clark; Shawn David Taylor; David O'brien; Yuesheng Cheng; Amin SAEEDFAR
Original assignee: Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Holdings Limited; Schlumberger Technology B.V.; Prad Research And Development Limited; Schlumberger Technology Corporation
Priority date: 2013-05-21
Filing date: 2013-09-11
Publication date: 2014-11-27

Abstract

Apparatus and methods for microwave heating of hydrocarbon fluid contained inside a tubular member that extends through the interior space of a resonant cavity. An electromagnetic (EM) source is configured to generate microwave radiation that is supplied to the resonant cavity. The EM source includes a control system that controls the frequency and power level of the microwave radiation that is supplied to the resonant cavity. The control system includes a temperature sensor that measures the temperature of the hydrocarbon fluid contained within the tubular member.

Description

APPARATUS AND METHOD EMPLOYING MICROWAVE RESONANT CAVITY

HEATING OF HYDROCARBON FLUID

BACKGROUND

Field

[0001] The present application relates generally to thermal processing of materials. More particularly, the present application relates to the use of electromagnetic energy (specifically microwave energy) to promote a chemical process or reaction, such as visbreaking of a hydrocarbon fluid where the molecular bonds in hydrocarbon molecules are broken so that smaller or lighter hydrocarbons are created in order to irreversibly reduce the viscosity of the hydrocarbon fluid.

Related Art

[0002] While heavy oil is becoming a regular feedstock to most refineries, its inherent high viscosity presents a significant challenge in transporting the heavy oil from the wellsite to commercial upgrading and refining facilities. A number of options have been or are currently used, including tanker shipments by rail, tanker truck, or barge, diluting of the heavy oil for pipeline transportation, and viscosity reduction by visbreaking for pipeline transportation.

[0003] The most common method of transport is blending heavy oils with diluents to reduce the viscosity to a lower value that makes pipeline transport of the heavy oil technically and economically feasible. The diluents may be solvents, condensate liquids, naphtha, or light conventional oils that are compatible with the heavy oils. Such methods require large and readily available volumes of diluents as well as infrastructure to blend, transport, and recover the diluents at the other end of the pipeline. Since the costs of diluents and pumping additional volumes of liquid are significant, alternative viscosity reduction methods that can be deployed at a wellsite location prior to pipeline transport are attractive.

[0004] Alternative approaches to reduce the viscosity at the wellsite typically involve chemically altering the composition of the heavy oil using a visbreaking process deployed within a surface facility (e.g., gas-fired visbreaker) or by in-situ upgrading techniques (e.g., electromagnetic (EM) heating techniques at radiowave (RF) or microwave (MW) frequencies).

[0005] Heavy oil has a high molecular weight fraction (typically referred to as a residual fraction) that distills at temperatures above 524°C. Visbreaking involves heating the heavy oil to a reaction temperature (typically in the range of 350°C to 500°C) where thermal cracking of the heavy oil will take place with relatively low conversion of the residual fraction. Typically, no more than 30 percent of the residual fraction of the heavy oil is converted, with the result being that just enough material is converted to reduce the viscosity but not significantly alter the quality of the heavy oil. Note that visbreaking is a different process than conventional upgrading (e.g., delayed cokers and fluidized bed cokers) where the composition of the feedstock is significantly altered to produce a higher quality oil for refining. Moreover, the conventional upgrading process typically handles large production volumes in the range of ten thousand to hundreds of thousands of barrels/day and requires expensive infrastructure to be viable and is therefore limited to refinery locations. However, visbreaking techniques at wellsite surface facilities can be more attractive for preparing pipeline-ready heavy oils since the production volumes are lower and such techniques involve reduced and simplified infrastructure. [0006] Visbreaking is typically carried out by a gas-fired heated tubular reactor that provides directional heating from outside to inside (i.e. heat flow from the tube wall to the oil contained inside the tube). While effective and relatively efficient, this mechanism introduces the risk of thermally-driven fouling on the inside of the reactor tube walls. The fouling, or buildup of insoluble coke particles on the tube walls, must be cleaned at regular maintenance intervals leading to scheduled shutdowns to replace and clean the reactor tubes.

SUMMARY

[0007] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0008] In an embodiment of the subject disclosure an apparatus and method is provided to heat hydrocarbon feedstock (such as heavy crude oil) by microwave radiation confined inside a resonant cavity. Microwave radiation is generated by an EM source (at RF or MW frequencies) and delivered to the resonant cavity by a power coupler, which may be an iris coupler. The resonant cavity is a sealed vessel that confines microwave radiation supplied thereto and supports resonance of the supplied microwave radiation at one or more resonant frequencies. The coupling strength of the power coupler that operably couples the EM source to the resonant cavity can be tuned such that the effective load impedance matches the output impedance of the EM source in order to maximize power transfer. The hydrocarbon feedstock is loaded into a pipe made of a material primarily transparent to the microwave radiation, such as sapphire. The pipe is configured to extend through the resonant cavity and to enter and exit the resonant cavity. In this manner, the hydrocarbon feedstock is contained within the interior space of the resonant cavity and physically isolated from the interior space of the resonant cavity by the pipe wall. The EM source includes a control system that controls frequency and power level of the microwave radiation that is supplied to the resonant cavity. The control system includes a temperature sensor that measures temperature of the hydrocarbon fluid contained within the tubular member.

[0009] In one embodiment, the EM source includes an EM signal generator and EM amplifier, wherein output of the EM signal generator is subject to amplification by the EM amplifier. The control system can be configured to interface with the EM signal generator to control the source frequency of the microwave radiation that is supplied to the resonant cavity, and the control system can be configured to interface to the EM amplifier to control power level of the microwave radiation that is supplied to the resonant cavity.

[0010] In one embodiment, the EM source includes an EM signal generator and EM amplifier, wherein output of the EM signal generator is subject to amplification by the EM amplifier. The control system can be configured to interface with a resonant cavity volume tuning mechanism to control the resonant frequency of the resonant cavity that receives the microwave radiation, and the control system can be configured to interface to the EM amplifier to control power level of the microwave radiation that is supplied to the resonant cavity.

[0011] The control system can include circuitry that measures resonant frequency of the resonant cavity, and the control system can be configured to interface to the EM signal generator in order to control frequency of the microwave radiation that is supplied to the resonant cavity such that it corresponds to the measured resonant frequency of the resonant cavity. The circuitry can be configured to measure resonant frequency of the resonant cavity based upon a measurement of at least one of incident microwave power, transmitted microwave power, and reflected microwave power of the apparatus.

[0012] The control system can also be configured to interface to the EM amplifier to control the power level of the microwave radiation that is supplied to the resonant cavity such that the hydrocarbon fluid contained inside the tubular member is heated to a desired heating temperature profile.

[0013] The control system can include first and second control blocks, where the first control block interfaces to the EM signal generator to control frequency of the microwave radiation that is supplied to the resonant cavity, and where the second control block is configured to interface to the EM amplifier to control the power level of the microwave radiation that is supplied to the resonant cavity. The first and second control blocks can have a configuration where the control operations of the first and second control blocks are performed in a continuous manner in parallel with respect to one another. The first control block can also have a configuration where the control operations of the first control block and possibly the second control block are performed in an intermittent manner.

[0014] The EM source, the resonant cavity, and the pipe can be configured to heat the hydrocarbon feedstock loaded into the pipe to a reaction temperature suitable for visbreaking of the hydrocarbon feedstock. In one embodiment, the reaction temperature is in the range of 350°C to 500°C, which is suitable for visbreaking of heavy crude oil feedstock (i.e., the thermal cracking of the heavy crude oil feedstock with relatively low conversion of the residual fraction such that the viscosity of the oil is reduced without significantly altering the quality of the oil). Pumps and valves can be fluidly coupled to the opposed ends of the pipe outside the resonant cavity and configured to provide a pressurized flow of the hydrocarbon feedstock through the pipe during the heating process such that it remains in a liquid phase so as to suppress the gas phase and avoid two-phase flow.

[0015] The resonant frequency(ies) supported by the resonant cavity can lie in a frequency band between 0.1 GHz and 100 GHz.

[0016] The resonant cavity can be configured to focus microwave radiation at the resonant frequency to a localized area within the internal space of the resonant cavity. This localized area can be occupied by the tubular member within the internal space of the resonant cavity for efficient heating. In one embodiment, the resonant cavity can be configured to resonate microwave radiation at a desired transverse magnetic (TM) or transverse (TE) mode, such as TMoio mode. In this case, the tubular member can extend along an axis of the resonant cavity defined by the TM₀io mode.

[0017] The resonant cavity can be defined by an elongate body having a longitudinal axis, and the tubular member can be configured to extend inside the resonant cavity along the longitudinal axis of the body. A plurality of thin members (e.g., discs) can be disposed along the longitudinal axis of the body. The members can define a series of resonant cavity sections with

corresponding interior spaces. The members can have apertures that are configured to allow for propagation of microwave radiation through the interior spaces of the series of resonant cavity sections. The tubular member can extend through the interior spaces of the series of resonant cavity sections to allow for heating of hydrocarbon fluid within the tubular member by microwave radiation confined within the interior spaces of the series of resonant cavity sections.

[0018] At least one soaker section can be disposed downstream of the resonant cavity. The soaker section is configured to contain hydrocarbon fluid and limit heat loss from the contained hydrocarbon fluid. The soaker section can include a tube or pipe or any pressure-containing vessel that contains the hydrocarbon fluid with thermally-insulative material that surrounds the tube or pipe or pressure vessel. The soaker section can also include an active heater element (such as heat tape or a heating coil) that is disposed between the thermally-insulative material and the tube or pipe or pressure vessel.

[0019] An inlet port and an outlet port can be sealably coupled to opposed ends of the tubular member outside the resonant cavity.

[0020] A thermally-insulative material that is primarily transparent to microwave radiation can surround the tubular member within the resonant cavity, and/or may be placed against the cavity wall.

[0021] The hydrocarbon fluid can flow at a controlled flow rate through the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity. Alternatively, the hydrocarbon fluid can remain stationary inside the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity.

[0022] The hydrocarbon fluid heated by the apparatus can be crude oil, heavy oil, or bitumen.

[0023] A mathematical model can be used to determine the size of the tubular member, the resonant frequency of the microwave radiation, the geometry of the resonant cavity that supports such resonant frequency, and the required residence time in order to carry out desired visbreaking of a given flow rate of hydrocarbon fluid. [0024] In another aspect, an apparatus for heating a hydrocarbon fluid with microwave radiation includes a plurality of microwave resonator heater sections, wherein each microwave resonator heater section includes a resonant cavity and a corresponding tubular member. The resonant cavity of a given microwave resonator heater section defines an interior space and is made of material that is primarily reflective to microwave radiation. The resonant cavity is a sealed vessel that confines microwave radiation supplied thereto and supports resonance of supplied microwave radiation at one or more resonant frequencies. The tubular member of the given microwave resonator heater section is configured to extend through the interior space of the resonant cavity and enter and exit the resonant cavity of the given microwave resonator heater section. The tubular member is made of material that is primarily transparent to microwave radiation. The plurality of microwave resonator heater sections are configured such that the tubular members of the plurality of microwave resonator heater sections contain hydrocarbon fluid that is subject to heating by microwave radiation confined within the interior spaces of the resonant cavities of the plurality of microwave resonator heater sections.

[0025] The resonant frequency(ies) supported by the resonant cavities of the plurality of microwave resonator heater sections can lie in a frequency band between 0.1 GHz and 100 GHz.

[0026] Multiple EM sources can supply microwave radiation to corresponding resonant cavity heater sections. An EM source can cooperate with a power splitter to split microwave radiation into multiple legs for supply to a number of the resonant cavity heater sections.

[0027] A flow splitter and associated tubing can distribute an inflow of hydrocarbon fluid to the tubular members of the plurality of microwave resonator heater sections. [0028] At least one soaker section can be disposed downstream of the plurality of microwave resonator heater sections. The soaker section is configured to contain hydrocarbon fluid and limit heat loss from the contained hydrocarbon fluid. The soaker section can include a tube or pipe or any pressure-containing vessel that contains the hydrocarbon fluid with thermally- insulative material that surrounds the tube or pipe or pressure vessel and/or may be placed against the soaker section wall. The soaker section can also include an active heater element (such as heat tape or a heating coil) that is disposed between the thermally-insulative material and the tube or pipe. A plurality of soaker sections can be disposed downstream of the plurality of microwave resonator heater sections.

[0029] Further features and advantages of the subject application will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present application is further described in the detailed description which follows, and in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the present application in which like reference numerals represent similar parts throughout the several views of the drawings.

[0031] FIG. 1 is a schematic cross-sectional view of an exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation confined in a resonant cavity.

[0032] FIG. 2 is a color diagram illustrating the amplitude of the electric field distribution in the resonant cavity of FIG. 1 during an exemplary visbreaking process. [0033] FIG. 3 is a color diagram illustrating the power loss density distribution in the resonant cavity of FIG. 1 during the exemplary visbreaking process.

[0034] FIG. 4 is a curve that shows the required inner diameter of the resonant cavity body of FIG. 1 operating at 2.45 GHz as a function of inner diameter of the hydrocarbon-containing pipe (with the pipe made of alumina and with a fluid pressure of 1000 psi (70.3 kg/square cm)). Such a curve can be created for any frequency, fluid pressure, and pipe material, which results in dimensional change of the apparatus shown in FIG. 1.

[0035] FIG. 5 is a plot of the reflection coefficient (Sn of the S-parameters) in the resonant cavity of FIG. 1 over a frequency range, which shows the TM₀io mode as well as its neighboring, undesired modes.

[0036] FIG. 6 is a schematic cross-sectional view of a second exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation confined in a resonant cavity.

[0037] FIG. 7 is a color diagram illustrating the amplitude of the electric field distribution in the resonant cavity of FIG. 6 during an exemplary visbreaking process.

[0038] FIG. 8 is a color diagram illustrating the power loss density distribution in the resonant cavity of FIG. 6 during the exemplary visbreaking process.

[0039] FIG. 9 is a schematic cross-sectional view of a third exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation confined in a resonant cavity. [0040] FIG. 10 is a color diagram illustrating the amplitude of the electric field distribution in the resonant cavity of FIG. 9 during an exemplary visbreaking process.

[0041] FIG. 1 1 is a color diagram illustrating the power loss density distribution in the resonant cavity of FIG. 9 during the exemplary visbreaking process.

[0042] FIG. 12A is a curve that illustrates the required inner diameter of the resonant cavity body of FIG. 9 for a TMoio mode operating at a resonant frequency of 2.45 GHz as a function of the inner diameter of the hydrocarbon-containing pipe.

[0043] FIG. 12B is a curve that illustrates the required inner diameter of the resonant cavity body of FIG. 9 for a TMoio mode operating at a resonant frequency of 0.3 GHz as a function of the inner diameter of the hydrocarbon-containing pipe.

[0044] FIG. 13 is a curve that illustrates the reflection coefficient (Sn of the S-parameters) in the resonant cavity of FIG. 9 as a function of frequency, which shows a single TMoio mode at a frequency at or near 2.45 GHz.

[0045] FIGS. 14A and 14B are top and front views, respectively, of an exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation; the apparatus employs four microwave resonator heater sections and one soaker section similar to the components of the design of FIG. 9.

[0046] FIGS. 15A and 15B are top and front views, respectively, of an exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation; the apparatus employs four microwave resonator heater sections and two soaker sections similar to the components of the design of FIG. 9. [0047] FIG. 16 is a schematic block diagram of an EM source that supplies microwave radiation to a resonant cavity heater as described herein.

[0048] FIG. 17 is a flow chart of an intermittent frequency track and heat control scheme carried out by a configuration of the EM source of FIG. 16.

[0049] FIG. 18 is a plot of a sweep operation carried out by the EM source of FIG. 16 in order to update the source frequency of the microwave radiation supplied to the resonant cavity heater such that it matches the resonant frequency of the resonant cavity heater.

[0050] FIG. 19 is a flow chart of a continuous frequency track and heat control scheme carried out by a configuration of the EM source of FIG. 16.

DETAILED DESCRIPTION

[0051] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present application only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present application. In this regard, no attempt is made to show structural details in more detail than is necessary for the fundamental understanding of the present application, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present application may be embodied in practice. Furthermore, like reference numbers and designations in the various drawings indicate like elements. [0052] In the present application, the high frequency signals used and referred to as microwaves, microwave radiation or energy, radio frequency (RF) radiation or energy, electromagnetic (EM) radiation or energy refer to electromagnetic waves within the microwave radio frequency band.

[0053] The term "dBm" is a power value in decibels (dB) referenced to one milliwatt of power.

[0054] The term "incident power" refers to the microwave power (preferably in dB or dBm or watts) being supplied to the resonant cavity heater, which may or may not include both amplitude and phase information.

[0055] The term "reflected power" refers to the microwave power (preferably in dB or dBm or watts) that is reflected from the resonant cavity heater, which may or may not include both amplitude and phase data.

[0056] The term "absorbed power" refers to the microwave power (preferably in dB or dBm or watts) that is absorbed by the resonant cavity heater and fluids contained therein, which may or may not include both amplitude and phase data.

[0057] The term "transmitted power" refers to the microwave power (preferably in dB or dBm or watts) that is transmitted through the resonant cavity heater, which may or may not include both amplitude and phase data.

[0058] The embodiments of the present application disclose apparatus and methods for microwave heating of a hydrocarbon feedstock (such as heavy crude oil) inside a resonant cavity defined by a body made of an electromagnetic conductive material. Microwave radiation is generated by an EM source and delivery system and supplied to the resonant cavity by a power coupler, which may be an iris coupler. The resonant cavity is a sealed vessel that confines microwave radiation supplied thereto and supports resonance of the supplied microwave radiation at one or more resonant frequencies. The impedance of the power coupler that operably couples the EM delivery system to the resonant cavity can be tuned such that the effective load impedance matches the output impedance of the EM delivery system in order to maximize power transfer. The hydrocarbon feedstock is loaded into a pipe made of a material primarily transparent to the microwave radiation, such as sapphire, quartz, or alumina. The pipe is configured to extend through the resonant cavity and to enter and exit the resonant cavity. In this manner, the hydrocarbon feedstock is contained within the interior space of the resonant cavity and physically isolated from the interior space of the resonant cavity by the pipe wall. The microwave radiation supplied to the resonant cavity, the resonant cavity itself, and the pipe can be configured to heat the hydrocarbon feedstock loaded into the pipe to a reaction temperature suitable for visbreaking of the hydrocarbon feedstock. In one embodiment, the reaction temperature is in the range of 350°C to 500°C, which is suitable for visbreaking of heavy crude oil feedstock (i.e., the thermal cracking of the heavy crude oil feedstock with relatively low conversion of the residual fraction such that the viscosity of the oil is reduced without significantly altering the quality of the oil). Pumps and valves can be fluidly coupled to the opposed ends of the pipe outside the resonant cavity and configured to provide a pressurized flow of the hydrocarbon feedstock through the pipe during the heating process such that it remains in a liquid phase so as to suppress the gas phase and avoid a two-phase flow.

[0059] The resonant cavity supports or facilitates at least one mode of electromagnetic radiation within the radio wave and microwave frequency band - the frequency band between 0.1 GHz and 100 GHz. As used herein, the term "mode" refers to a particular pattern of a standing electromagnetic wave that satisfies Maxwell's equations and the applicable boundary conditions of the resonant cavity. In the cavity, the mode can be any one of the various possible patterns of standing electromagnetic waves. Each mode is characterized by its frequency and standing wave pattern. The electromagnetic wave pattern of a mode depends on the frequency, refractive indices, or dielectric constants of the materials of the cavity, the pipe and the hydrocarbon, and the cavity geometry.

[0060] A transverse electric (TE) mode is one whose electric field vector is normal to a particular plane of reference. Similarly, a transverse magnetic (TM) mode is one whose magnetic field vector is normal to a particular plane of reference.

[0061] The actual field distribution inside the resonant cavity is a superposition of the modes therein. Each of the modes can be identified with one or more subscripts (e.g., TE₀₁₀). Each subscript attributes to the boundary condition in a particular dimension in the three geometric dimensional Maxwell's equations. For a resonant cavity, each of the three geometric dimensions has one boundary condition, resulting in three subscripts. For standing wave, or resonant, modes, the modes are discreet and the subscripts are integers. In general, the larger a particular subscript the more modes are present in the standing wave in that particular geometric dimension. The resonant frequencies of different modes have different sensitivity to the geometric dimensions, so the density and distribution of the mode frequencies in the frequency spectrum of a particular resonant cavity depends on the ratio of its geometric dimensions. It is possible to manipulate the ratio of the geometric dimensions of a resonant cavity to locate the mode of interest, e.g. TM₀io, to a region in the frequency spectrum where the mode density is relatively low, which reinforces single mode resonation. In case the frequency of the mode of interest is near or overlaps with the frequencies of one or more other modes, simultaneous resonation of more than one mode can occur. The resulting electromagnetic field pattern will be the superposition of the fields of individual modes, which in general does not show the same types of strong maxima and minima field values within the cavity.

[0062] FIG. 1 illustrates an embodiment of an apparatus 11 for visbreaking of a hydrocarbon feedstock (such as heavy crude oil) through focused heating by microwave radiation inside a resonant cavity. The resonant cavity is defined by an elongate cylindrical body 13 of circular cross-section and opposed end caps 15. The body 13 and end caps 15 are made of a metallic material (such as aluminum, stainless steel, copper, bronze, or any electrically conductive metal) that is primarily reflective of microwave radiation with minimal absorption. Each end cap 15 includes an outward extending neck 17 that defines a central passageway through the respective end cap 15. In this manner, the end caps 15 are configured to receive and support a pipe 19 that extends through the end caps 15 and through the center of the body 13 along the central longitudinal axis of the elongate body 13. The pipe 19 is made of a nonconductive material (such as sapphire, quartz, ceramic, alumina, or other suitable material) that is primarily transparent to microwave radiation. The opposed ends of the pipe 19 that extend beyond the respective necks 17 of the end caps 15 interface to corresponding ported tube receptacles 21. Each ported tube receptacle 21 is shouldered on a support flange 23 and retained to the support flange 23 by a retainer 25. The support flange 23 is fastened to tie rods 27 that are fastened to the respective end cap 15 as shown. A high pressure seal 29 is provided for each ported tube receptacle 21 adjacent the interface of the ported tube receptacle 21 and the respective support flange 23 in order to prevent fluid leakage at this joint.

[0063] The hydrocarbon feedstock 31 to be treated is loaded inside the pipe 19 and is physically isolated from the body 13 of the resonant cavity. A temperature sensor 33 that is formed of a material that is primarily transparent to microwave radiation, such as a single-crystal sapphire optical fiber temperature sensor, can be inserted inside the pipe 19 and placed in direct contact with the hydrocarbon feedstock 31. The temperature sensor 33 can extend through the pipe 19 outside the resonant cavity through neck 17 and corresponding ported tube receptacle 21 such that it is coupled to associated light processing equipment for deriving temperature of the hydrocarbon feedstock 31 at one more positions inside the pipe 19 during the visbreaking process. Pumps and valves can be fluidly coupled to the opposed ported tube receptacles 21 and configured to supply a pressurized flow of the hydrocarbon feedstock 31 inside the pipe 19 during the visbreaking process such that it remains in a liquid phase so as to suppress the gas phase and avoid two phase flow in the pipe 19. This provides better control by minimizing the variability in the residence time and temperature profiles experienced by the hydrocarbon feedstock during the visbreaking process, which in turn provides improved control of the targeted visbreaking reactions. In one embodiment, the hydrocarbon feedstock flow is pressurized up to 5000 psi (351.5 kg/square cm) inside the pipe 19 during the visbreaking process such that it remains in a liquid phase so as to suppress the gas phase and avoid two phase flow in the pipe 19.

[0064] An EM source is configured to generate and supply microwave radiation via a waveguide or coaxial cable or transmission line to a coupler 35 which interfaces to the body 13. The coupler 35 guides the supplied microwave radiation into the body 13 and can provide for impedance matching of the power transmission system to the impedance of the body 13. There are many designs available for the coupler 35, including but not limited to iris couplers and loop couplers. FIG. 1 shows an iris coupler design which comprises a waveguide 37 and plate 39 with a tuned iris geometry attached to the outside of the body 13. The waveguide 37 and plate 39 are realized from a metallic material (such as aluminum, stainless steel, copper, bronze, or any electrically conductive metal) that is primarily reflective of microwave radiation with minimal absorption. The resonant cavity defined by the body 13 and end caps 15 can be elongate in nature with the coupler 35 disposed nearer one end of the resonant cavity (and thus further away from the other end of the resonant cavity) as evident from FIGS. 2 and 3.

[0065] The microwave energy generated and supplied by the EM source is centered at a predefined frequency, which can range between 0.1 and 10 GHz depending on the specific flow rate requirements of the system as described below in more detail. The geometry of the resonant cavity defined by the body 13 and end caps 15 is configured to resonate at the predefined frequency of the microwave energy generated and supplied by the EM source. Furthermore, the microwave energy and the resonant cavity and the pipe 19 are configured to heat the

hydrocarbon feedstock loaded into the pipe 19 to a reaction temperature suitable for visbreaking of the hydrocarbon feedstock. In one embodiment, the reaction temperature is in the range of 350°C to 500°C, which is suitable for visbreaking of heavy crude oil feedstock (i.e., the thermal cracking of the heavy crude oil feedstock with relatively low conversion of the residual fraction such that the viscosity of the oil is reduced without significantly altering the quality of the oil). In all cases, the geometry of the resonant cavity can be configured to ensure that the vast majority of the microwave energy in the cavity is concentrated along the central axis of the pipe 19. The material of the body 13, the end caps 15, and the coupler 35 is optimized to minimize microwave energy reflection, and enable a high-Q resonant cavity, and thereby allow the maximum amount of microwave energy to heat the hydrocarbon feedstock fluid to the desired reaction temperature, while avoiding coke buildup on the inside walls of the pipe 19. If allowed to form on the pipe walls, coke will ultimately lead to the loss of cavity resonance - an undesired outcome. This can be achieved by operating the resonant cavity in an optimal TMoio mode with the option of operating at additional single TM and TE modes. TE modes can also be excited, for example, simply by rotating the coupler 35 and the corresponding iris by 90 degrees.

[0066] The design of the resonant cavity (body 13 and end caps 15) is configured to provide the maximum and most efficient energy transfer into the hydrocarbon fluid flowing in the pipe 19. Through microwave power coupling optimization and impedance matching, the resonant cavity can be tuned in order to minimize the reflected power from, or equivalently, to maximize the transmitted power into the resonant cavity for the desired transverse magnetic (TM) or transverse electric (TE) mode. The minimized reflected power, or equivalently the maximized transmitted power, results in the maximum energy transfer into the resonant cavity and thus the most efficient operation. In order to deliver the microwave energy to the relatively low loss hydrocarbon feedstock whose dielectric loss tangent is on the order of 10^~3 to 10^~2, the heating process requires the microwave energy to be focused on the center of the resonant cavity along the length of the pipe 19 and hence achieves a desired heating profile in the hydrocarbon feedstock and avoids "hot spots." In order to meet this requirement, the resonant cavity can be designed to operate at a single TMoio mode with the ability to operate at additional single TM and TE modes if desired. Additional undesired modes can be suppressed through mechanical means or electrical means or avoided by a precise frequency tracking technique.

[0067] FIG. 2 shows the amplitude of the electric field distribution in the resonant cavity of FIG. 1 during the visbreaking process. FIG. 3 shows the power loss density distribution in the resonant cavity of FIG. 1 during the visbreaking process. In both FIGS. 2 and 3, the microwave energy has a TMoio mode at a resonant frequency of 2.45 GHz. The results are desirable since the majority of the microwave energy is focused on the hydrocarbon feedstock contained inside the pipe 19 and thus provides efficient and controlled heating of the hydrocarbon feedstock. [0068] The thermal reactions (i.e. upgrading reactions) of the visbreaking process are controlled by flowing the hydrocarbon feedstock in a liquid phase through the resonant cavity defined by the body 13 and end caps 15. The hydrocarbon feedstock enters the resonant cavity from the end of the pipe 19 closest to the coupler 35. The hydrocarbon feedstock then flows through the pipe 19 past the coupler 35 and exits the pipe 19 at the end furthest from the coupler 35. In the case of FIG. 1, the fluid flow of the hydrocarbon feedstock is from right to left. In the case of FIGS. 2 and 3, the fluid flow of the hydrocarbon feedstock is from left to right. As indicated by FIG. 2, as the hydrocarbon feedstock flows through the pipe 19 and into the resonant cavity, it is exposed to a rapidly increasing power intensity which leads to rapid heating. The peak rate of heating occurs as the hydrocarbon feedstock passes by the coupler 35, after which the rate of heating decreases. At this point, the hydrocarbon feedstock is at or close to the desired

(upgrading) reaction temperature, which can be in the range of 350°C to 500°C. As the hydrocarbon feedstock travels the remaining length of the pipe 19 within the resonant cavity, the rate of heating continues to decrease towards a minimal level. This provides enough heating to ensure the reaction temperature is maintained within the desired operating range of the resonant cavity.

[0069] The amount of conversion (i.e., visbreaking) of the hydrocarbon feedstock is dictated by the amount of time that the hydrocarbon feedstock remains at the desired reaction temperature, also known as the residence time. The desired flow rate, the length of the pipe 19 inside the resonant cavity (i.e., the resonant cavity length), and the inner diameter of the pipe 19 of the apparatus of FIG. 1 can be used to determine the residence time. Therefore, the apparatus of FIG. 1 may accommodate larger flow rates by increasing the diameter of the pipe 19. For the case where a TM₀io mode is desired, the microwave energy is focused on the center of the pipe 19. In this case, in order to accommodate an increase in the pipe diameter, the inside diameter of the resonant cavity body 13 must increase to accommodate a decrease in the operating resonant frequency. FIG. 4 is a curve based on mathematical analysis using a perturbation technique that shows the required inner diameter of the resonant cavity body 13 operating at 2.45 GHz as a function of the inner diameter of the pipe 19 with the pipe made of alumina and with a fluid pressure of 1000 psi (70.3 kg/square cm). Such a curve can be created for any frequency, fluid pressure, and pipe material, which results in dimensional change of the apparatus shown in FIG. 1. Practically, the only dimension affecting the cavity design operating at the TMoio mode is the inner diameter of the resonant cavity body 13 and not its length (i.e., the dimension along the length of the pipe 19). This is a particular advantage of the TMoio mode in a cylindrical resonant cavity because the resonant cavity can be of arbitrary length without changing the operating frequency of the TMoio mode. The apparatus of FIG. 1 can also be configured to accommodate larger flow rates by other mechanisms, such as by adding one or more additional resonant cavity heater sections (similar the resonant cavity heater section of FIG. 1) configured in a parallel arrangement (similar to FIGS. 14A/14B and 15A/15B) or in a series arrangement, if desired.

[0070] The apparatus of FIG. 1 can employ well known monitoring and control mechanisms to maintain the desired resonance mode (e.g., TMoio mode) and the desired heating efficiency, as well as the desired fluid temperature during the visbreaking process. FIG. 5 is a plot of the reflection coefficient (Sn of the S-parameters) over a frequency range showing the TMoio mode as well as its neighboring, undesired modes. Resonance control may be achieved by i) frequency tracking, where the power source frequency is frequently updated to maintain the desired resonance mode and/or ii) by the use of tuning mechanisms to control the volume of the resonant cavity, including, but not limited to, mechanical, thermal, and electromagnetic measures. Resonance control can involve monitoring and assurance of the minimization of the reflection coefficient (Sn of the S-parameters) or of the maximization of the transmission coefficient (S₂₁ of the S-parameters) during the visbreaking process. Temperature control can utilize the temperature sensor 33 to detect the temperature of the hydrocarbon feedstock and control the level of microwave power in order to achieve the desired reaction temperature of the visbreaking process.

[0071] The location of the coupler 35 can be dictated by the desired location for rapid heating of the hydrocarbon feedstock. For example, the coupler 35 can be located anywhere along the length of the resonant cavity. In the exemplary design of FIG. 1, the coupler 35 is located closer to the inlet end of the resonant cavity, where the hydrocarbon feedstock enters into the resonant cavity. This can provide rapid heating of the hydrocarbon feedstock to the desired reaction temperature immediately upon entry to the resonant cavity. The remaining length of the resonant cavity is then left to maintain the reaction temperature of the hydrocarbon fluid to the exit port.

[0072] Advantageously, the apparatus of FIG. 1 produces rapid heating of the hydrocarbon feedstock while maintaining relatively cool temperatures on the walls of the resonant cavity body 13 and end caps 15. A thermally-insulative material that is primarily transparent to microwave radiation can be used to cover the pipe 19 containing the hydrocarbon feedstock inside the resonant cavity body 13 of FIG. 1 in order to limit heat loss (and thus reduce the energy input requirements of the EM source) and maintain the desired reaction temperature.

[0073] FIG. 6 illustrates an embodiment of an apparatus 111 for visbreaking of a hydrocarbon feedstock (such as heavy crude oil) through focused heating by microwave radiation inside a resonant cavity. The apparatus 111 of FIG. 6 is fundamentally the same as the apparatus 11 of FIG. 1 except for the addition of metallic thin discs 41 that are disposed inside the elongate body 13 and extend transverse to the longitudinal axis of the elongate body 13 and the pipe 19. The discs 41 are spaced from one another along the length of the elongate body 13 to define a number of shorter-length resonant cavities that are disposed adjacent one another within the body 13. The sequence of shorter-length resonant cavities is disposed adjacent a main resonant cavity (the resonant cavity adjacent the pipe inlet and the coupler 35). In this configuration, the adjacent shorter-length resonant cavities may be coupled to the main resonant cavity and to one another through apertures in the discs 41. The shorter-length resonant cavities behave like single mode cavities by suppressing other modes. Apertures in the discs 41 allow for signal attenuation as microwave energy propagates from the main resonant cavity through the sequence of shorter- length resonant cavities. The metallic surfaces of the discs 41 also function to mirror the microwave signal in each respective cavity, which lessens the attenuation of the signal and increases the overall heating length of the hydrocarbon feedstock inside the pipe 19. In addition, by configuring the number of discs 41 and their locations along the axis of the body 13, the focus of electric field intensity can be changed so that a designated part of the hydrocarbon feedstock receives more microwave energy. Moreover, the number of employed discs 41 , their spacing and the aperture size on each disc 41 can be optimized for performance enhancement. The main resonant cavity and the adjacent sequence of shorter length resonant cavities mimic the operation of a multi-mode resonator cavity. The main resonant cavity can operate with a TMoio mode, if desired. In this case, a frequency tracking system can be used to ensure the main resonant cavity is operating at the frequency of the desired resonance mode (e.g., TM₀io mode).

[0074] FIG. 7 shows the amplitude of the electric field distribution in the resonant cavity of FIG. 6 during the visbreaking process. FIG. 8 shows the power loss density distribution in the resonant cavity of FIG. 6 during the visbreaking process. In both FIGS. 7 and 8, the microwave energy has a TMoio mode at a resonant frequency of 2.45 GHz. The results are desirable since the majority of the microwave energy is focused on the hydrocarbon feedstock contained inside the pipe 19 and thus provides efficient and controlled heating of the hydrocarbon feedstock.

[0075] The thermal reactions (i.e., upgrading reactions) of the visbreaking process are controlled by flowing the hydrocarbon feedstock in a liquid phase through the main resonant cavity and the shorter- length resonant cavities, where such resonant cavities are defined by the body 13 and end caps 15 and the discs 41. The hydrocarbon feedstock enters into the end of the pipe 19 closest to the coupler 35 and flows through the pipe 19 within the main resonant cavity supplied with microwave radiation via the coupler 35. The hydrocarbon feedstock then flows through the pipe 19 into the shorter-length resonant cavities and exits the body 13 at the end furthest from the coupler 35. In the case of FIG. 6, the fluid flow of the hydrocarbon feedstock is from right to left. In the case of FIGS. 7 and 8, the fluid flow of the hydrocarbon feedstock is from left to right. As indicated by FIG. 7, as the hydrocarbon feedstock flows through the pipe 19 and into the main resonant cavity, it is exposed to a rapidly increasing power intensity which leads to rapid heating. The peak rate of heating occurs as the hydrocarbon feedstock passes by the coupler 35, after which the rate of heating decreases. At this point, the hydrocarbon feedstock is at or close to the desired (upgrading) reaction temperature, which can be in the range of 350°C to 500°C. As the hydrocarbon feedstock travels through the remaining length of the pipe 19 within the shorter-length resonant cavities defined by the discs 41, the rate of heating continues to decrease towards a minimal level. This provides enough heating to ensure the reaction temperature is maintained within the desired operating range of the apparatus. [0076] For the apparatus of FIG. 6, the desired flow rate, the length of the pipe 19 extending through the main resonant cavity and the smaller-size resonant cavities (i.e., the total resonant cavity length), and the inner diameter of the pipe 19 can be used to determine the residence time of the hydrocarbon feedstock flowing within the pipe 19. Similar to the apparatus of FIG. 1 , the apparatus of FIG. 6 may accommodate larger flow rates by increasing the diameter of the pipe 19. For the case where a TM₀io mode is desired, the microwave energy is focused on the center of the pipe 19. In this case, in order to accommodate an increase in the pipe diameter, the inner diameter of the resonant cavity body 13 must increase to accommodate a decrease in the operating resonant frequency. The apparatus of FIG. 6 can also be configured to accommodate larger flow rates by other mechanisms, such as by adding one or more additional resonant cavity heater sections (similar to the resonant cavity heater section of FIG. 6) configured in a parallel arrangement (similar to FIGS. 14A/14B and 15A/15B) or in a series arrangement, if desired. A thermally-insulative material that is primarily transparent to microwave radiation can be used to cover the tube 19 containing the hydrocarbon feedstock inside the resonant cavity body 13 of FIG. 6 in order to limit heat loss (and thus reduce the energy input requirements of the EM source) and maintain the desired reaction temperature.

[0077] FIG. 9 illustrates an embodiment of an apparatus 1111 for visbreaking of a hydrocarbon feedstock (such as heavy crude oil) through focused heating by microwave radiation inside a resonant cavity. The apparatus 1111 of FIG. 9 is fundamentally the same as the apparatus 11 of FIG. 1 except for the addition of a soaker section 43 disposed outside the resonant cavity defined by the body 13 and end caps 15. The soaker section 43 covers a length of the pipe 19 downstream of the resonant cavity. The soaker section 43 provides insulation or/and heating to such length of pipe 19 and to the hydrocarbon feedstock disposed therein in order to ensure the desired reaction temperature of the hydrocarbon feedstock is maintained over such length of pipe 19. The soaker section 43 can be realized by one or more layers of thermally-insulative material, such as mineral fiber, glass fiber, silica, aerogel, or other suitable insulating material, that surrounds the length of pipe 19. Such thermally-insulative material insulates the length of pipe to minimize conductive heat loss from the hydrocarbon feedstock disposed in the length of pipe. The soaker section 43 can also include resistive heat tape or heater coil wrapped around the length of pipe under the thermally-insulative material. The resistive heat tape or heater coil can be configured to apply heat to the length of pipe 19 and to the hydrocarbon feedstock disposed therein as desired. The resonant cavity can operate with a TMoio mode, if desired. In this case, a frequency tracking system can be used to ensure the resonant cavity is operating at the optimal frequency of the desired resonant mode (e.g., TM₀io mode).

[0078] FIG. 10 shows the amplitude of the electric field distribution in the resonant cavity of FIG. 9 during the visbreaking process. FIG. 1 1 shows the power loss density distribution in the resonant cavity of FIG. 9 during the visbreaking process. In both FIGS. 10 and 1 1 , the microwave energy has a TMoio mode at a resonant frequency of 2.45 GHz. The results are desirable since the majority of the microwave energy is focused on the hydrocarbon feedstock contained inside the pipe 19 and thus provides efficient and controlled heating of the

hydrocarbon feedstock.

[0079] The thermal reactions (i.e. upgrading reactions) of the visbreaking process are controlled by flowing the hydrocarbon feedstock in a liquid phase through the resonant cavity defined by the body 13 and end caps 15. The hydrocarbon feedstock enters the resonant cavity from the end of the pipe 19 closest to the coupler 35. The hydrocarbon fluid then flows through the pipe 19 past the coupler 35 and into the soaker section 43 and exits the pipe 13 at the end furthest from the coupler 35. In the case of FIGS. 9 to 11, the fluid flow of the hydrocarbon feedstock is from right to left. As indicated by FIG. 9, as the hydrocarbon feedstock flows through the pipe 19 and into the resonant cavity, it is exposed to a rapidly increasing power intensity which leads to rapid heating. The peak rate of heating occurs as the hydrocarbon feedstock passes by the coupler 35, after which the rate of heating decreases. At this point, the hydrocarbon feedstock is at or close to the desired (upgrading) reaction temperature, which can be in the range of 350°C to 500°C. As the hydrocarbon feedstock travels through the length of the pipe 19 in the soaker section 43, the soaker section 43 provides insulation and/or heating to such length of pipe 19 and to the hydrocarbon feedstock disposed therein in order to ensure the reaction temperature of the hydrocarbon feedstock is maintained over such length of pipe 19. This provides enough heating to ensure the reaction temperature is maintained within the desired operating range of the resonant cavity over the length of the soaker section. Advantageously, the soaker section 43 provides a relatively accurate control over the level and the uniformity of the temperature profile of the hydrocarbon feedstock necessary for the visbreaking to occur.

[0080] For the apparatus of FIG. 9, the desired flow rate, the length of the pipe 19 extending through the resonant cavity (i.e., the resonant cavity length) together with the length of pipe 19 of the soaker section 43, and the inner diameter of the pipe 19 can be used to determine the residence time of the hydrocarbon feedstock flowing within the pipe 19. The apparatus of FIG. 9 can be configured to accommodate larger flow rates by using any combination of i) increasing the diameter of the pipe 19 and the resonant cavity body 13, ii) adding one or more additional resonant cavity heater sections (similar the resonant cavity heater section of FIGS. 9, 10 and 11) configured in a parallel arrangement (FIGS. 14A/14B and 15A/15B) or a serial arrangement, iii) increasing the dimensions (e.g. length and diameter of a cylinder) of the soaker section 43, and iv) adding one or more additional soaker sections (similar the soaker section 43 of FIG. 9) configured in a parallel arrangement (FIGS. 15A/15B). For the case where a TMoio mode is desired, the microwave energy is focused on the center of the pipe 19. In this case, in order to accommodate an increase in the pipe diameter, the inside diameter of the resonant cavity body 13 must increase to accommodate a decrease in the operating frequency. FIG. 12A is a curve that illustrates the required inner diameter of the resonant cavity body 13 as a function of the inner diameter of the pipe 19 for a TMoio mode at a resonant frequency 2.45 GHz. FIG. 12B is a curve that illustrates the required inner diameter of the resonant cavity body 13 as a function of the inner diameter of the pipe 19 for a TMoio mode at a resonant frequency of 0.3 GHz. This shows that a decrease in the resonant frequency from 2.45 GHz to 0.3 GHz will allow for an increase in the maximum diameter of the pipe 19 that can be accommodated in the resonant cavity.

Following this approach, a range of flow rates may be achieved by simply adjusting the resonant frequency and the inner diameter of the resonant cavity body 13 in order to maintain the desired resonance mode; in most cases, the TMoio mode.

[0081] Compared to the apparatus of FIGS. 1 and 6, the use of the soaker section 43 outside the resonant cavity decreases the length-to-diameter ratio of the resonant cavity. Among the complete TE and TM mode spectrum, the TMoio mode has a unique property that its frequency is cavity-length-independent, whereas other modes exhibit an increase in frequency as the cavity's length-to-diameter ratio decreases. FIG. 13 illustrates the reflection coefficient (Sn of the S- parameters in dB) in an exemplary embodiment of the resonant cavity of FIG. 9 as a function of frequency, which shows a single TMoio mode at a frequency at or near 2.45 GHz. Such single TMoio mode operation significantly simplifies any necessary resonance control mechanism and results in higher energy efficiency and lower design and hardware costs, such as suppression of neighboring modes. Also, the microwave coupler 35 of the apparatus of FIG. 9 is located at the center of the resonant cavity body 13, which enables a longitudinally symmetric EM field pattern, which enhances the stability of the desired longitudinal temperature profile along the length of the pipe 19 inside the resonant cavity. The enhanced stability results in higher energy efficiency and significantly simplifies resonance control, such as field profile monitoring.

[0082] It should be noted that the apparatus of FIG. 9 employs a pipe 19 (of material primarily transparent to microwave radiation) that extends along the entire length of the central axis of the resonant cavity as well as the entire length of the soaker section 43. Note that transparency to microwave radiation is only required in the resonant cavity. Thus, the hydrocarbon fluid that flows through the soaker section 43 can be contained inside a pipe, cylindrical vessel, or vessel of any shape made of a metallic material that is non-transparent to microwave radiation, such as stainless steel, nickel alloy, or other material strong enough for the pressure conditions of the visbreaking process. Thermally-insulative material can surround the pipe or vessel of the soaker section 43 to limit heat loss. An active heater element, such as heat tape or a heater coil, can be used to heat the fluid in the soaker section, if desired. A thermally-insulative material that is primarily transparent to microwave radiation can be used to cover the tube 19 containing the hydrocarbon feedstock inside the resonant cavity body 13 of FIG. 9 in order to limit heat loss (and thus reduce the energy input requirements of the EM source) and maintain the desired reaction temperature.

[0083] As mentioned above, scaling of the apparatus of FIG. 9 to achieve higher flow rates can be performed by using different combinations of the resonant cavity heater sections and soaker sections (vessels). In all cases, the hydrocarbon feedstock flows into the microwave resonant cavity heater sections followed by the soaker section(s). The number of microwave resonant cavity heater sections is dictated by the flow rate of the inflow of hydrocarbon feedstock that is to be processed (upgraded) and the flow rate capacity of each resonant cavity heater section or the given pipe volume and required residence time. The number of soaker sections (or vessels) will depend on the volume requirement, required residence time, and operational restrictions, such as physical space, pressure handling capabilities, and flow restrictions.

[0084] For illustrative purposes, two possible examples of apparatus for larger flow rates are shown in FIGS. 14A/4B and 15A/15B. In the apparatus of FIGS. 14A/14B, the inflow of the hydrocarbon feedstock 10 is divided by a flow splitter and associated tubing to a parallel arrangement of four microwave resonant cavity heaters similar to the design of FIGS. 9, 10, and 11 that bring the hydrocarbon fluid to the desired reaction temperature using microwave energy supplied at 12. The output flow of the four microwave resonant cavity heaters is combined and fed into a single soaker vessel, where the hydrocarbon fluid is allowed to remain for the desired residence time before exiting the apparatus at 14. In the apparatus of FIGS. 15A/15B, the inflow of the hydrocarbon feedstock 10 is divided by a flow splitter and associated tubing to a parallel arrangement of four microwave resonant cavity heaters similar to the apparatus of FIGS. 9, 10, and 11 that bring the hydrocarbon fluid to the desired reaction temperature using microwave energy supplied at 12. The output flow of the four microwave resonant cavity heaters is combined and fed into a parallel arrangement of two soaker vessels, where the hydrocarbon fluid is allowed to remain for the desired residence time before exiting the apparatus at 14. In both apparatus, the four microwave resonant cavity heaters and the soaker vessels are similar to the respective parts of FIGS. 9, 10, and 11 as described above.

[0085] The apparatus of FIGS. 14A/14B and 15A/15B can employ multiple EM sources and delivery systems for supplying the microwave radiation to corresponding resonant cavity heaters of the apparatus. Alternatively, a single EM source and delivery system can employ a power splitter to split the microwave radiation into multiple legs for supply to the resonant cavity heaters of the apparatus. In other configurations, multiple EM source and delivery systems and one or more power splitters can be used to supply the microwave radiation to the resonant cavity heaters of the apparatus.

[0086] The apparatus of FIGS. 14A/14B and 15A/15B can also employ well known monitoring and control mechanisms to maintain the desired resonance mode (e.g., TMoio mode) and heating efficiency, as well as the desired fluid temperature during the visbreaking process. Resonance control may be achieved by i) frequency tracking, where the power source frequency is frequently updated to maintain the desired resonance mode and/or ii) by the use of tuning mechanisms to control the volume of the resonant cavity, including, but not limited to, mechanical, thermal, and electromagnetic measures. Resonance control can involve monitoring and assurance of the minimization of the reflection coefficient (Sn of the S-parameters) or of the maximization of the transmission coefficient (S₂₁ of the S-parameters) during the visbreaking process. Temperature control can utilize the temperature sensor 33 to detect the temperature of the hydrocarbon feedstock and control the level of microwave power in order to achieve the desired reaction temperature of the visbreaking process.

[0087] Table 1 is a summary of exemplary calculations illustrating how scaling of the resonant cavity of the apparatus of FIG. 9 can be achieved. Table 1

where "Resonant Residence Time" is the total time (in seconds) that the hydrocarbon feedstock is heated inside the microwave resonant cavity to provide the

Temperature Increase to the desired reaction temperature;

"Temperature Increase" is the temperature increase (in °C) from the temperature of the hydrocarbon feedstock at the inlet to the desired reaction temperature in the resonant cavity; "Resonant Frequency" is the resonant frequency (in GHz) of the microwave resonant cavity;

"Operating ID_pipe" is the inner diameter (in cm) of the pipe 19;

"Flow Rate" is the flow rate (in barrels per day or BPD) of the hydrocarbon feedstock that flows through the pipe 19;

"Cavity Diameter" is the inner diameter (in cm) of the resonant cavity body 13 that contains the pipe 19; it is dictated by Resonant Frequency; and

"Cavity Length" is the length (in cm) of the resonant cavity body 13; it is dictated by the Flow Rate and the inner diameter of the pipe 19 to satisfy the desired Resonant Residence Time.

[0088] In the exemplary Table 1, it is assumed that a Resonant Residence Time of 30 seconds is required for the case where the microwave radiation in the resonant cavity heats the hydrocarbon feedstock from an initial temperature below the 350-500°C range of the reaction temperature to a desired reaction temperature within the 350-500°C for the visbreaking process. In this manner, the microwave radiation heats the hydrocarbon feedstock to raise its temperature by 100°C. In order to provide the hydrocarbon feedstock at the initial temperature (100°C less than the desired reaction temperature), the hydrocarbon feedstock can be preheated. Such preheating reduces the amount of microwave energy that is required to heat the hydrocarbon feedstock to the desired reaction temperature for thermal visbreaking. Such preheating can be carried out through conventional means, such as electric, gas fired, coal burning, or other suitable fluid heating schemes. Table 1 can be derived from practical maximum diameters determined from plots like FIGS. 12A and 12B. Then, for each operating resonant frequency, it is possible to determine the dimensions of the resonant cavity and the flow rate that can be achieved.

[0089] For example, referring to the fifth row of Table 1, for a flow of hydrocarbon feedstock (i.e., heavy crude oil) at a rate of 0.26 BPD and a required Resonant Residence Time of 30 seconds to heat the hydrocarbon feedstock from a temperature of 310°C (after preheating) to a reaction temperature of 410°C (a temperature increase of 100°C), the resonant cavity of the apparatus of FIG. 9 can be configured to operate at a resonant frequency of 2.45 GHz with a resonant cavity inner diameter of 7.37 cm and a pipe inner diameter of 1.00 cm. In this case, the length of the resonant cavity is 18.4 cm as dictated by the hydrocarbon feedstock flow rate of 0.26 BPD and the 1.00 cm inner diameter of the pipe 19 to satisfy the desired Resonant

Residence Time of 30 seconds.

[0090] In another example, referring to the last row of Table 1 , for a flow of hydrocarbon feedstock (i.e., heavy crude oil) at a rate of 150.00 BPD and a required Resonant Residence Time of 30 seconds to heat the hydrocarbon feedstock from a temperature of 340°C (after preheating) to a reaction temperature of 440°C (a temperature increase of 100°C), the resonant cavity of the apparatus of FIG. 9 can be configured to operate at a resonant frequency of 0.300 GHz with a resonant cavity inner diameter of 58.32 cm and an inner pipe diameter of 8.50 cm. In this case, the length of the resonant cavity is 146.0 cm as dictated by the hydrocarbon feedstock flow rate of 150.00 BPD and the 8.50 cm inner diameter of the pipe 19 to satisfy the desired Resonant Residence Time of 30 seconds. [0091] The residence time of the hydrocarbon feedstock flowing through the system necessary for the visbreaking process is a function of the reaction temperature. Higher reaction

temperatures require shorter residence times. Table 2 below illustrates exemplary reaction temperatures and residence times for heavy crude oil.

Table 2

[0092] Referring to the second row of Table 2, a reaction temperature of 410°C requires a residence time of 32 minutes. In this case, the heavy crude oil feedstock is preheated to a temperature of or near 310°C and the resonant cavity operates to heat the heavy crude oil feedstock to or near the reaction temperature of 410°C. The soaker section 43 is configured to maintain the heated hydrocarbon feedstock at the reaction temperature for 31.5 minutes (with the resonant cavity providing the necessary heating for the remaining 0.5 minutes of the requisite 32 minute residence time). The soaker section 43 can be one vessel (similar to the apparatus of FIGS. 14A/14B), a parallel arrangement of vessels (similar to the apparatus of FIGS 15A/15B) or a series arrangement of vessels, if desired. [0093] Referring to the third row of Table 2, a reaction temperature of 440°C requires a residence time of 8 minutes. In this case, the heavy crude oil feedstock is preheated to a temperature of or near 340°C and the resonant cavity operates to heat the heavy crude oil feedstock to or near the reaction temperature of 440°C. The soaker section 43 is configured to maintain the heated hydrocarbon feedstock at the reaction temperature for 7.5 minutes (with the resonant cavity providing the necessary heating for the remaining 0.5 minutes of the requisite 8 minute residence time). The soaker section 43 can be one vessel (similar to the apparatus of FIGS. 14A/14B), a parallel arrangement of vessels (similar to the apparatus of FIGS 15A/15B) or a series arrangement of vessels, if desired.

[0094] It is also contemplated that multiple microwave resonant cavities can be fluidly coupled to the downstream soaker section or vessel(s). The multiple microwave resonant cavities can be arranged in a parallel arrangement (similar to the apparatus of FIGS. 14A/14B and 15A/15B) or a series arrangement, if desired. In the parallel configuration, the hydrocarbon fluid inflow is distributed over the multiple resonant cavities by a flow splitter and associated tubing, which reduces the necessary resonant cavity length. In the series configuration, the multiple cavity lengths can be added together to realize the necessary cavity length, which allows for a reduction in length of the respective individual resonant cavity.

[0095] Other configurations follow from the other reaction temperatures and corresponding residence times listed in Table 2. A similar approach can be used to configure the apparatus of FIGS. 1 and 6 to support a variety of reaction temperatures and corresponding residence times.

[0096] It is contemplated that the hydrocarbon fluid will flow at a controlled flow rate through the apparatus during the visbreaking process as described herein. In other embodiments, the valves and pumps can be configured to control the hydrocarbon fluid flow such that it remains stationary within the apparatus during the visbreaking process.

[0097] Contrary to conventional heating techniques, the visbreaking of the hydrocarbon feedstock by heating through microwave radiation results in localized heating through the oscillating of polar and non-polar molecules in the hydrocarbon feedstock, which results in heating the hydrocarbon feedstock from within. This internal heating prevents thermally driven fouling from occurring on the interior wall of the pipe inside the resonant cavity(ies) of the apparatus. The use of microwave heating also offers the advantage of more rapid heating of a targeted volume of hydrocarbon feedstock and offers the potential for economically visbreaking smaller production volumes. The apparatus and methodology of visbreaking can be used to irreversibly reduce the viscosity of a variety of hydrocarbon fluids, such as heavy crude oil, other viscous crude oil, and bitumen.

[0098] The apparatus as described herein have a small footprint as compared to the traditional systems for upgrading heavy oil. The apparatus may be located at a wellsite or in a production field so that the heavy oil may be upgraded before it is transported from the wellsite or production field. It is contemplated that the apparatus can be mounted on skids or trucks and brought to the wellsite or production field for use.

[0099] The resonant cavity of the apparatus as described herein employs a cylindrical cross- sectional shape. Other cross-sectional shapes, such as rectangular cross-sectional shapes, can also be used for the resonant cavity.

[00100] Referring now to FIG.16, according to the present disclosure, an EM source 160 including an EM signal generator 162 (which can be realized by a voltage-controlled oscillator or other electronic oscillator) and an EM amplifier 164 cooperate to supply microwave radiation to a waveguide or coaxial cable or transmission line 166 that delivers the microwave radiation to the power coupler 35 of the resonant cavity heater 1 1 (or multiple resonant cavity heater sections) as described above. The EM source 160 also includes a control system that interfaces to the EM signal generator 162 and the EM amplifier 164 to control the power level of the microwave radiation supplied to the waveguide or coaxial cable or transmission line 166 in order to control the microwave heating of the hydrocarbon fluid within the resonant cavity heater(s) 1 1. The control system includes a resonant frequency tracking control block 168, an EM power control block 170, and a main control block 172. The control system can be realized by a software-programmed computer processing system with appropriate interface circuitry or other suitable controller device.

[00101] The resonant frequency tracking control block 168 directly or indirectly monitors the resonant frequency of the resonant cavity heater 1 1 that characterizes a desired mode (such as a TMoio mode) to be established in the resonant cavity heater 1 1 and controls the EM signal generator 162 to output an EM signal at such resonant frequency. Note that the resonant frequency of the resonant cavity heater 1 1 can change over time due to factors such as changes in the dimensions of the cavity arising from temperature variations of the environment of the resonant cavity heater 1 1 or changes in the composition of the hydrocarbon fluid (e.g. changes in the heavy oil composition feeding the reactor). The EM power control block 170 monitors the temperature profile of the hydrocarbon fluid in the resonant cavity heater 1 1 and controls the gain of the EM amplifier 164 to control the power level of the microwave energy supplied to the waveguide or coaxial cable or transmission line 166 in order to obtain the desired rate of heating inside the resonant cavity heater 1 1. The main control block 172 interfaces to both the resonant frequency tracking control block 168 and the EM power control block 170 to carry out a desired control scheme.

[00102] In one implementation, the main control block 172 is configured to carry out an intermittent frequency track and heat control scheme as outlined in FIG. 17, which begins in step 1701 where the EM power control block sets the output power of the EM amplifier 164 to a predetermined level. In one embodiment, the predetermined level is a low power level in which the power of the anticipated reflected waves is minimized while allowing for accurate measurement of the frequency response, the goal being to reduce the power of the standing waves and the power loss during the measurement process. With the output power of the EM amplifier 164 at the predetermined level set in step 1701 , the resonant frequency tracking control block 168 performs a sweep function in step 1703. The sweep function of step 1703 measures the resonant frequency of the resonant cavity heater 1 1 that characterizes the desired mode (such as a TMoio mode) to be established in the resonant cavity heater 1 1. One way to measure such resonant frequency is to measure the frequency response of the resonant cavity heater 1 1 and identify the resonant frequency of the target mode (i.e., the TMoio mode). A schematic representation of the frequency sweep of step 1703 is shown in FIG. 18. In measuring the frequency response of the resonant cavity heater 1 1 , the EM signal generator 162 can be configured to generate a wide spectrum yet high definition source frequency signal in a short period of time. The resonant frequency tracking control block 168 can operate in step 1705 to process the required change in the source frequency of the EM signal generator 162 that matches the new resonant frequency and can update the source frequency of the EM signal generator 162 accordingly in step 1707. [00103] With the source frequency of the EM signal generator 162 set to the resonant frequency of the resonant cavity heater 11, the main control block 172 initiates a heating mode carried out by the EM power control block 170 in steps 1709 to 1713. In the heating mode, the EM signal generator 162 is configured to generate a continuous mode or pulsed-mode EM signal for supply to the resonant cavity heater 11 via the waveguide or coaxial cable or transmission line 166 in order to heat the hydrocarbon fluid in the resonant cavity heater 11 to a desired visbreaking temperature in the 350°C to 500°C range. In the case of the embodiments shown in FIG. 1 and FIG. 6, the temperature sensor can be located at the expected area of peak temperature within the pipe 19. Specifically, in step 1709, the EM power control block 170 measures the hydrocarbon fluid temperature inside the resonant cavity heater 11 one or more times in order to characterize the temperature profile of the hydrocarbon fluid in the resonant cavity heater 11. In step 1711, the EM power control block 170 can utilize the fluid temperature measurement(s) of step 1709 to calculate the required change in the gain of the EM amplifier 164 to produce the energy needed for heating the hydrocarbon fluid to the desired visbreaking temperature in the resonant cavity heater 11, and can update the gain of the EM amplifier 164 accordingly in step 1713. The EM power control block 170 can use a feedback control algorithm to control the gain of the EM amplifier 164. For example, a PID control algorithm can be used where the gain of the EM amplifier 164 is the manipulated variable and the measured hydrocarbon fluid temperature inside the resonant cavity heater 11 is the process variable with its set point dictated by the desired visbreaking temperature of the hydrocarbon fluid inside the resonant cavity heater 11 , In other embodiments, the gain of the EM amplifier 164 in the heating mode can be fixed by design or set manually by an operator. The gain of the EM amplifier 164 is generally represented as a percentage of maximum range from 0-100%, or can be calculated as a percentage range in dB (logarithmic scaling) or a percentage range in watts (linear scaling).

[00104] In steps 1715 to 1719, the main control block 172 is configured to initiate the sweep function of step 1703 in a periodic manner in order to maintain resonance during heating. One of the two different cycle control schemes of steps 1717 and 1719 can be used.

[00105] In the cycle control scheme of step 1717, the cycle duration of the heating mode is timed and settable, for example, 10 seconds per heating cycle. When the duration of the heating cycle has expired, the sweep function of step 1703 is initiated. Otherwise, the heating mode of steps 1703 to 1707 continues without performing the sweep function.

[00106] In the cycle control scheme of step 1719, the cycle duration of heating mode is dictated by a settable trip point based upon the reflected power, the transmitted power, or the absorbed power of the microwave energy of the system. Specifically, as the resonance of the resonant cavity system changes during operation, the reflected power percentage increases and the transmitted and absorbed percentage of power will drop. When these power signals cross the settable trip point, the sweep function of step 1703 is initiated. Otherwise, the heating mode of steps 1709 to 1713 continues without performing the sweep function. The cycle control scheme of step 1719 increases the overall efficiency of the system by allowing continual heating while the system is stable and triggering the sweep cycle only when resonance changes cause the efficiency to drop. In either scheme of steps 1717 and 1719, once the given heating cycle is complete, the main control block 172 triggers the EM power control block 170 to reduce the power output of the EM amplifier 164 in step 1701 prior to initiating the next sweep function (step 1703). [00107] In another implementation, the main control block 172 is configured to carry out a continuous frequency track and heat control scheme as outlined in FIG. 19. In the continuous frequency track and heat control scheme, the EM signal generator 162 is configured to generate a continuous mode or pulsed-mode EM signal for supply to the resonant cavity heater 11 via the waveguide or coaxial cable or transmission line 166 for heating the hydrocarbon fluid in the resonant cavity heater 11. Furthermore, the resonant frequency tracking control block 168 is configured to continuously perform a cycle of steps 1901 to 1905 that monitors and calculates the resonant frequency of the resonant cavity heater 11 and updates the source frequency of the EM signal generator 162 to match the measured resonant frequency of the resonant cavity heater 11. The resonant frequency tracking control block 168 can be configured to measure the resonant frequency of the resonant cavity heater 11 by monitoring the electrical phase difference between the incident power and the transmitted power of the microwave energy of the system in step 1903. The reflected power of the microwave energy of the system can be monitored using a dual directional coupler that is part of the waveguide or coaxial cable or transmission line 166. The transmitted power of the microwave energy of the system can be monitored by a probe or port integral to the resonant cavity heater 11. At resonance, the electrical phase difference between the incident and transmitted power can be measured and stored as a "zero-phase- difference" value, i.e., the electrical phase difference where the two power signals are in phase. The electrical phase difference can be derived by a frequency mixing circuit in which the electrical phase difference is represented by a DC voltage output of the circuit. As the resonant frequency changes, the electrical phase difference between the incident and transmitted power deviates from the "zero-phase-difference" value. Based on this deviation, the resonant frequency tracking control block 168 can calculate the required change in the source frequency of the EM signal generator 162 that matches the new resonant frequency in step 1903 and can update the source frequency of the EM signal generator 162 accordingly in step 1905. The resonant frequency tracking control block can utilize a feedback control algorithm to control the source frequency of the EM signal generator 162. For example, a PID control algorithm can be used where the source frequency of the RF signal generator 162 is the manipulated variable and the detected phase difference is the process variable with its set point dictated by the "zero-phase- difference" value. The sampling frequency of the incident power, reflected power and transmitted power of the system can be dictated by a number of factors (such as the stability of the resonant frequency) with the goal of maximizing system efficiency.

[00108] With the source frequency of the EM signal generator 162 updated continuously by the cyclical operations carried out by the resonant frequency tracking control block in steps 1901 to 1905, the main control block 172 is configured to control the EM power control block 170 to perform a heating operation in parallel with the resonant frequency tracking control of steps 1901 to 1905. In the heating operation, which is shown as steps 1907 to 1911 in FIG. 19, the gain of the EM amplifier 164 is controlled to control the power level of the microwave energy supplied to the waveguide or coaxial cable or transmission line 166 to obtain the desired visbreaking temperature in the range of 350°C to 500°C of the hydrocarbon fluid inside the resonant cavity heater 11. In the case of the embodiment shown in FIG. 9, the temperature sensor can be located either within the pipe 19 inside the body 13 at the expected area of peak temperature of the hydrocarbon fluid or at a position within the pipe 19 where the hydrocarbon fluid exits the body 13. Specifically, in step 1907, the EM power control block 170 measures the hydrocarbon fluid temperature inside the resonant cavity heater 11 one or more times in order to characterize the temperature of the hydrocarbon fluid inside the resonant cavity heater 11. In step 1909, the EM power control block 170 can utilize the fluid temperature measurement(s) of step 1907 to calculate the required change in the gain of the EM amplifier 164 to produce the energy needed for heating the hydrocarbon fluid to the desired temperature inside the resonant cavity heater 11 , and can update the gain of the EM amplifier 164 accordingly in step 1911. The EM power control block 170 can use a feedback control algorithm to control the gain of the EM amplifier 164. For example, a PID control algorithm can be used where the gain of the EM amplifier 164 is the manipulated variable and the measured hydrocarbon fluid temperature inside the resonant cavity heater 11 is the process variable with its set point dictated by the desired visbreaking temperature in the range of 350°C to 500°C of the hydrocarbon fluid inside the resonant cavity heater 11. In other embodiments, the gain of the EM amplifier 164 in the heating operation can be fixed by design or set manually by an operator. The gain of the EM amplifier 164 is generally represented as a percentage of maximum range from 0-100%, or can be calculated as a percentage range in dB (logarithmic scaling) or a percentage range in watts (linear scaling).

[00109] In other embodiments step 1707 of the intermittent frequency track and heat control scheme of FIG. 17 and step 1905 of the continuous frequency track and heat scheme of FIG. 19 may be replaced by a step which tunes the resonant frequency of the resonant cavity heater 11 to match the source frequency of the EM signal generator 162. The tuning of the resonant frequency can be achieved by adjusting the volume of the resonant cavity. Volume adjustment mechanisms include, but are not limited to, mechanical, thermal, and electromagnetic measures. An example of such a mechanical measure is the use of one or more mechanically controlled plungers inserted into the resonant cavity. The plunger(s) may be made of a material consistent with that used to form the resonant cavity. [00110] The heating operations of steps 1907 to 1911 and the resonant frequency tracking operations of steps 1901 to 1905 of FIG. 19 continue until terminated by the main control block 172 in step 1913. Such termination can be triggered by operator input or by automatic means as desired (for example, when flow through the resonant cavity heater 11 is stopped).

[00111] In other embodiments of the continuous frequency track and heat scheme, step 1901 can be replaced by a relatively narrow sweep function measuring the reflected power or the transmitted power of the microwave energy of the system. With this scheme, while at the desired power level for heating operations the source frequency of the EM signal generator 162 is varied a small amount within the resonant band using the last measured or calculated resonant frequency as the center frequency. The power measurement(s) is(are) then used to calculate any change in the resonant frequency of the resonant cavity heater 11 and a new center sweep frequency is used as the resonance changes. The feedback rate of this scheme largely depends on the speed and accuracy of the power measurements.

[00112] In other embodiments, the main control block 172 can be configured to carry out the continuous frequency track and heat control scheme as outlined in FIG. 19 as the predominant control mode for highest operating efficiency with the intermittent frequency track and heat control scheme as outlined in FIG. 17 carried out in cases where a loss of control is caused by abrupt disturbances within the system. This provides the highest efficiency during normal operation with the ability to recover from extreme disturbances within the system.

[00113] In either control scheme a thermocouple, fiber optic temperature sensor, infrared, or other appropriate temperature sensor 174 may be used as part of the control system to monitor the temperature of the hydrocarbon fluid contained within the tubular member of the resonant cavity heater 11 as shown in FIG. 16. In order to measure the temperature of the hydrocarbon fluid contained within the tubular member of the resonant cavity heater 11 while preventing disturbances to the electromagnetic field, the temperature sensor 174 is preferably made of non- metallic material, such as a fiber optic temperature sensor 33 as described above.

[00114] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words 'means for' together with an associated function.

Claims

CLAIMS What is claimed is:

1. An apparatus for heating a hydrocarbon fluid with microwave radiation, comprising:

a resonant cavity defining an interior space and characterized by a resonant frequency; a tubular member extending through the interior space of the resonant cavity and entering and exiting the resonant cavity, the tubular member configured to contain hydrocarbon fluid that is subject to heating by microwave radiation confined within the interior space of the resonant cavity;

an apparatus for tuning the resonant frequency of the resonant cavity by adjusting the volume of the resonant cavity; and

an EM source configured to generate microwave radiation that is supplied to the resonant cavity, wherein the EM source includes a control system that controls power level of the microwave radiation that is supplied to the resonant cavity, the control system including a temperature sensor that measures temperature of the hydrocarbon fluid contained within the tubular member.

2. An apparatus according to claim 1, wherein the apparatus for tuning the resonant frequency of the resonant cavity comprises a plunger inserted into the resonant cavity.

3. An apparatus for heating a hydrocarbon fiuid with microwave radiation, comprising:

a resonant cavity defining an interior space; a tubular member extending through the interior space of the resonant cavity and entering and exiting the resonant cavity, the tubular member configured to contain hydrocarbon fluid that is subject to heating by microwave radiation confined within the interior space of the resonant cavity; and

an EM source configured to generate microwave radiation that is supplied to the resonant cavity, wherein the EM source includes a control system that controls frequency and power level of the microwave radiation that is supplied to the resonant cavity, the control system including a temperature sensor that measures temperature of the hydrocarbon fluid contained within the tubular member.

4. An apparatus according to claim 3, wherein the EM source includes an EM signal generator and EM amplifier, wherein output of the EM signal generator is subject to amplification by the EM amplifier, the control system is configured to interface with the EM signal generator to control frequency of the microwave radiation that is supplied to the resonant cavity, and the control system is configured to interface with the EM amplifier to control power level of the microwave radiation that is supplied to the resonant cavity.

5. An apparatus according to claim 4, wherein the control system includes circuitry that measures resonant frequency of the resonant cavity, and the control system is configured to interface with the EM signal generator in order to control frequency of the microwave radiation that is supplied to the resonant cavity such that it corresponds to the measured resonant frequency of the resonant cavity.

6. An apparatus according to claim 5, wherein the circuitry measures resonant frequency of the resonant cavity based upon a measurement of at least one of incident microwave power, transmitted microwave power, and reflected microwave power of the apparatus.

7. An apparatus according to claim 6, wherein the circuitry is configured to measure resonant frequency of the resonant cavity by measuring phase difference between incident microwave power and transmitted microwave power of the apparatus.

8. An apparatus according to claim 4, wherein the control system is configured to interface with the EM amplifier to control power level of the microwave radiation that is supplied to the resonant cavity such that the temperature of hydrocarbon fluid contained inside the tubular member is raised to a desired level.

9. An apparatus according to claim 3, wherein the control system includes a first control block that interfaces to the EM signal generator to control frequency of the microwave radiation that is supplied to the resonant cavity, and the control system includes a second control block that interfaces with the EM amplifier to control power level of the microwave radiation that is supplied to the resonant cavity.

10. An apparatus according to claim 9, wherein the first and second control blocks have a configuration where the control operations of the first and second control blocks are performed in a continuous manner in parallel with respect to one another.

11. An apparatus according to claim 9, wherein the first control block has a configuration where the control operation of the first control block is performed in an intermittent manner.

12. An apparatus according to claim 11, wherein the control operation of the second control block is triggered by a condition involving expiration of a timer or at least one measurement of microwave power of the system.

13. An apparatus according to claim 3, wherein the resonant cavity is made of material that is primarily reflective to microwave radiation, and is configured to confine microwave radiation within its interior space, and the tubular member is made of material that is primarily transparent to microwave radiation.

14. An apparatus according to claim 3, wherein the resonant cavity is configured to produce a predetermined standing wave pattern of the microwave radiation at a predefined resonant frequency.

15. An apparatus according to claim 14, wherein said resonant frequency lies in a frequency band between 0.1 GHz and 100 GHz.

16. An apparatus according to claim 14, wherein the resonant cavity is configured to focus the microwave radiation at the resonant frequency to a localized area within the interior space of the resonant cavity, wherein the localized area is occupied by the tubular member within the interior space of the resonant cavity.

17. An apparatus according to claim 16, wherein the resonant cavity is configured to resonate microwave radiation at a desired TM or TE mode.

18. An apparatus according to claim 17, wherein the resonant cavity is configured to resonate microwave radiation at a desired TMoio mode such that the focused microwave radiation in the localized area within the interior space of the resonant cavity lies along an axis of the resonant cavity defined by the TM₀io mode.

19. An apparatus according to claim 18, wherein the tubular member extends along the axis of the resonant cavity defined by the TM₀io mode.

20. An apparatus according to claim 3, wherein the hydrocarbon fluid is heated by the microwave radiation confined within the interior space of the resonant cavity to a desired temperature for visbreaking of the hydrocarbon fluid in order to irreversibly reduce viscosity of the hydrocarbon fluid.

21. An apparatus according to claim 20, wherein the desired temperature for visbreaking of the hydrocarbon fluid is in the range between 350°C and 500°C.

22. An apparatus according to claim 20, wherein pressure of the hydrocarbon fluid inside the tubular member is controlled such that the hydrocarbon fluid remains in a single liquid phase while being heated by the microwave radiation confined within the interior space of the resonant cavity.

23. An apparatus according to claim 22, wherein the pressure of the hydrocarbon fluid inside the tubular member is controlled to a desired pressure between atmospheric pressure and 5000 psi (351.3 kg/square cm).

24. An apparatus according to claim 3, wherein the hydrocarbon fluid flows at a controlled flow rate through the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity.

25. An apparatus according to claim 3, wherein the hydrocarbon fluid remains stationary inside the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity.

26. An apparatus according to claim 3, wherein the hydrocarbon fluid is selected from the group consisting of crude oil, heavy oil, and bitumen.

27. A method for heating a hydrocarbon fluid with microwave radiation, comprising:

supplying microwave radiation to a resonant cavity defining an interior space, the resonant cavity configured to confine the microwave radiation within its interior space and characterized by a resonant frequency; loading hydrocarbon fluid into a tubular member extending through the interior space of the resonant cavity and entering and exiting the resonant cavity, wherein the hydrocarbon fluid loaded into the tubular member is subject to heating by microwave radiation confined within the interior space of resonant cavity;

tuning the resonant frequency of the resonant cavity by adjusting the volume of the resonant cavity; and

controlling power level of the microwave radiation that is supplied to the resonant cavity, the controlling based upon measurement of temperature of the hydrocarbon fluid contained within the tubular member.

28. A method for heating a hydrocarbon fluid with microwave radiation, comprising:

supplying microwave radiation to a resonant cavity defining an interior space, the resonant cavity configured to confine the microwave radiation within its interior space;

loading hydrocarbon fluid into a tubular member extending through the interior space of the resonant cavity and entering and exiting the resonant cavity, wherein the hydrocarbon fluid loaded into the tubular member is subject to heating by microwave radiation confined within the interior space of the resonant cavity; and

controlling frequency and power level of the microwave radiation that is supplied to the resonant cavity, the controlling based upon measurement of temperature of the hydrocarbon fluid contained within the tubular member.

29. A method according to claim 28, wherein the controlling controls frequency of the microwave radiation that is supplied to the resonant cavity such that it corresponds to a measured resonant frequency of the resonant cavity, wherein the measured resonant frequency of the resonant cavity is derived from a measurement of at least one of incident microwave power, transmitted microwave power, and reflected microwave power of the system.

30. A method according to claim 29, wherein the measured resonant frequency of the resonant cavity is derived by measuring phase difference between incident microwave power and transmitted microwave power of the system.

31. A method according to claim 28, wherein the controlling controls power level of the microwave radiation that is supplied to the resonant cavity such that the temperature of hydrocarbon fluid contained inside the tubular member is raised to a desired level.

32. A method according to claim 28, wherein the controlling is carried out by a first control block and a second control block, the first control block configured to interface to an EM signal generator to control frequency of the microwave radiation that is supplied to the resonant cavity, and the second control block configured to interface to an EM amplifier to control power level of the microwave radiation that is supplied to the resonant cavity.

33. A method according to claim 32, wherein the first and second control blocks have a configuration where the control operations of the first and second control blocks are performed in a continuous manner in parallel with respect to one another.

34. A method according to claim 32, wherein the first control block has a configuration where the control operation of the first control block is performed in an intermittent manner.

35. A method according to claim 34, wherein the control operation of the first control block is triggered by a condition involving expiration of a timer or at least one measurement of microwave power of the system.

36. A method according to claim 34, wherein the control operation of the second control block is triggered by a condition involving expiration of a timer or at least one measurement of microwave power of the system.

37. A method according to claim 28, wherein the resonant cavity is made of a material that is primarily reflective to microwave radiation, the resonant cavity is configured to confine microwave radiation within its interior space, and the tubular member is made of a material that is primarily transparent to microwave radiation.

38. A method according to claim 28, wherein the resonant cavity is configured to produce a predetermined standing wave pattern of the microwave radiation at a predefined resonant frequency.

39. A method according to claim 38, wherein the resonant frequency lies in a frequency band between 0.1 GHz and 100 GHz.