Patent Application
20150068706
The present invention relates to the field of radio frequency (RF) equipment, and, more particularly, to an apparatus for processing hydrocarbon resources using RF heating and related methods.
Energy consumption worldwide is generally increasing, and conventional hydrocarbon resources are being consumed. In an attempt to meet demand, the exploitation of unconventional resources may be desired. For example, highly viscous hydrocarbon resources, such as heavy oils, may be trapped in sands where their viscous nature does not permit conventional oil well production. This category of hydrocarbon resource is generally referred to as oil sands. Estimates are that trillions of barrels of oil reserves may be found in such oil sand formations.
In some instances, these oil sand deposits are currently extracted via open-pit mining. Another approach for in situ extraction for deeper deposits is known as Steam-Assisted Gravity Drainage (SAGD). The heavy oil is immobile at reservoir temperatures, and therefore, the oil is typically heated to reduce its viscosity and mobilize the oil flow. In SAGD, pairs of injector and producer wells are formed to be laterally extending in the ground. Each pair of injector/producer wells includes a lower producer well and an upper injector well. The injector/production wells are typically located in the payzone of the subterranean formation between an underburden layer and an overburden layer.
The upper injector well is used to typically inject steam, and the lower producer well collects the heated crude oil or bitumen that flows out of the formation, along with any water from the condensation of injected steam. The injected steam forms a steam chamber that expands vertically and horizontally in the formation. The heat from the steam reduces the viscosity of the heavy crude oil or bitumen, which allows it to flow down into the lower producer well where it is collected and recovered. The steam and gases rise due to their lower density. Gases, such as methane, carbon dioxide, and hydrogen sulfide, for example, may tend to rise in the steam chamber and fill the void space left by the oil defining an insulating layer above the steam. Oil and water flow is by gravity driven drainage urged into the lower producer well.
Many countries in the world have large deposits of oil sands, including the United States, Russia, and various countries in the Middle East. Oil sands may represent as much as two-thirds of the world's total petroleum resource, with at least 1.7 trillion barrels in the Canadian Athabasca Oil Sands, for example. At the present time, only Canada has a large-scale commercial oil sands industry, though a small amount of oil from oil sands is also produced in Venezuela. Because of increasing oil sands production, Canada has become the largest single supplier of oil and products to the United States. Oil sands now are the source of almost half of Canada's oil production, while Venezuelan production has been declining in recent years. Oil is not yet produced from oil sands on a significant level in other countries.
U.S. Published Patent Application No. 2010/0078163 to Banerjee et al. discloses a hydrocarbon recovery process whereby three wells are provided: an uppermost well used to inject water, a middle well used to introduce microwaves into the reservoir, and a lowermost well for production. A microwave generator generates microwaves which are directed into a zone above the middle well through a series of waveguides. The frequency of the microwaves is at a frequency substantially equivalent to the resonant frequency of the water so that the water is heated.
Along these lines, U.S. Published Patent Application No. 2010/0294489 to Dreher, Jr. et al. discloses using microwaves to provide heating. An activator is injected below the surface and is heated by the microwaves, and the activator then heats the heavy oil in the production well. U.S. Published Patent Application No. 2010/0294488 to Wheeler et al. discloses a similar approach.
U.S. Pat. No. 7,441,597 to Kasevich discloses using a radio frequency generator to apply radio frequency (RF) energy to a horizontal portion of an RF well positioned above a horizontal portion of an oil/gas producing well. The viscosity of the oil is reduced as a result of the RF energy, which causes the oil to drain due to gravity. The oil is recovered through the oil/gas producing well.
U.S. Pat. No. 7,891,421, also to Kasevich, discloses a choke assembly coupled to an outer conductor of a coaxial cable in a horizontal portion of a well. The inner conductor of the coaxial cable is coupled to a contact ring. An insulator is between the choke assembly and the contact ring. The coaxial cable is coupled to an RF source to apply RF energy to the horizontal portion of the well.
Unfortunately, long production times, for example, due to a failed start-up, to extract oil using SAGD may lead to significant heat loss to the adjacent soil, excessive consumption of steam, and a high cost for recovery. Significant water resources are also typically used to recover oil using SAGD, which impacts the environment. Limited water resources may also limit oil recovery. SAGD is also not an available process in permafrost regions, for example, or in areas that may lack sufficient cap rock, are considered “thin” payzones, or payzones that have interstitial layers of shale.
Increased power applied within the subterranean formation may result in antenna component heating. One factor that may contribute to the increased heating may be the length of the coaxial transmission line, for example. Component heating for the antenna may be undesirable, and may result in less efficient hydrocarbon resource recovery, for example.
A typical coaxial feed geometry may not allow for adequate flow of a cooling fluid based upon a relatively large difference in hydraulic volume between inner and outer conductors of the coaxial feed. More particularly, a typical coaxial feed may be assembled by bolted flanges with compressed face seals, for example. The coaxial feed also includes a small inner conductor with a standoff for the signal voltage. However, the typical coaxial feed may not be developed for use with a coolant and for increased thermal performance. Moreover, hydraulic volumes of the inner and outer conductors may be significantly different, which may affect overall thermal performance.
To more efficiently recover hydrocarbon resources, it may be desirable to inject a solvent, for example, in the subterranean formation. For example, the solvent may increase the effects of the RF antenna on the hydrocarbon resources. One approach for injecting a solvent within the subterranean formation includes the use of sidetrack wells that are typically used for instruction and are separate from the tubular conductors used for hydrocarbon resource recovery.
U.S. Patent Application Publication No. 2005/0103497 to Gondouin discloses a down-hole flow control apparatus, super-insulated tubular, and surface tools for producing heavy oil by steam injection. More particularly, Gondouin discloses using two dedicated and super-insulated vertical tubulars, coaxially carrying wet steam at the center, surrounded by heated oil through the coldest part of their environment.
U.S. Pat. No. 7,770,602 to Buschhoff discloses a double wall pipe. More particularly, Buschhoff discloses a double wall pipe with an inner high pressure pipe having an inner flow space for liquids. The double wall pipe also includes an outer protection pipe coaxially arranged around the inner pipe. The outer pipe has longitudinal grooves on an inner surface. The inner high pressure pipe is fitted tightly into the outer protection pipe.
It may thus be desirable to provide increased efficiency hydrocarbon resource recovery. More particularly, it may be desirable to provide increased cooling and/or coolant liquid injection along with an RF antenna.
In view of the foregoing background, it is therefore an object of the present invention to provide a hydrocarbon resource processing apparatus that provides increased heat removal.
This and other objects, features, and advantages in accordance with the present invention are provided by an apparatus for processing hydrocarbon resources in a subterranean formation that includes a radio frequency (RF) source, a dielectric cooling liquid source, and an RF applicator in the subterranean formation and coupled to the RF source to supply RF power to the hydrocarbon resources. The RF applicator includes a plurality of concentric tubular conductors defining cooling passageways therebetween coupled to the dielectric cooling fluid source. At least one property of the dielectric cooling liquid, a flow rate of the dielectric cooling liquid, and a configuration of the cooling passageways cooperate to generate a turbulent flow of the dielectric cooling liquid adjacent surfaces of the plurality of concentric tubular conductors to thereby enhance thermal transfer.
The at least one property of the dielectric cooling liquid may include a density and a viscosity. The dielectric cooling liquid source may include a dielectric cooling liquid supply and a heat exchanger. The dielectric cooling liquid may include mineral oil, for example.
A method aspect is directed to a method of processing hydrocarbon resources in a subterranean formation using an apparatus that includes a radio frequency (RF) source, a dielectric cooling liquid source, an RF applicator in the subterranean formation and coupled to the RF source to supply RF power to the hydrocarbon resources, and a plurality of concentric tubular conductors defining cooling passageways therebetween coupled to the dielectric cooling fluid source. The method includes generating a turbulent flow of the dielectric cooling liquid adjacent surfaces of the plurality of concentric tubular conductors to thereby enhance thermal transfer by at least configuring at least one property of the dielectric cooling liquid, configuring a flow rate of the dielectric cooling liquid, and configuring the cooling passageways.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.
Referring initially to
Referring now additionally to
The RF applicator 30 includes an RF transmission line 33 in the form of an RF coaxial transmission line. One of the concentric tubular conductors 31a advantageously defines the inner conductor of the RF coaxial transmission line 33, and the other of the concentric tubular conductors 31b defines the outer conductor of the RF coaxial transmission line.
Heating of the hydrocarbon resources within the subterranean formation 21 involves the use of relatively high voltages, for example, several kilovolts to tens of kilovolts. In some examples, supplied RF power may be up to 10 kW/m, have a relatively low associated power loss, for example less than 5%, and have a typical dissipation at 5 kW/m of about 100 W/m. Operation of a coaxial RF transmission line 33 at a temperature of less than 150° C., and, more particularly, 100° C. is desirable for increasingly reliable operation. Limited use of seals, spacers, and fluids may provide some cooling. However, this may not be sufficient for desired cooling.
Referring particularly to
The third electrically conductive sleeve 38 should generally be electrically isolated from the second electrically conductive sleeve 36. For ordinary wire dipoles in air, this may be accomplished by space or spacing, for example, air space, between the legs of the RF dipole antenna 34, or two dipole halves. However, for an installation, for example, as described herein, wherein the two legs of RF dipole antenna 34, or dipole halves, are to be mechanically connected for purposes of deployment in the wellbore 24, the two dipole halves may be separated by an isolator, for example, similar to dielectric tubular spacer 37 described herein.
Of course, while an RF dipole antenna is described herein, it will be appreciated that other types of RF antennas may be used, and may be configured with the RF transmission line in other arrangements. Additionally, while a balun, and more specifically a quarter wave balun, has been described, it will be appreciated that other elements, for example, a choke, such as a magnetic choke balun, may be alternatively or additionally used.
A startup temperature near the RF dipole antenna 34 may reach up to 260° C., and in-situ hydrocarbon recovery processes may reach temperatures of up to 700° C. Corrosive materials, such as, for example, steam, H2S, and salts, may be also be present within the wellbore 24. With particular respect to the RF dipole antenna 34, there is a relatively high field intensity near the antenna during the supplying of RF power. Spacing and/or insulating materials may limit the temperature adjacent isolator sections, for example. However, a temperature of less than 200° C., and more preferably, less than 150° C. is desirable. Thus, it may be particularly desirable to provide additional or increased cooling, especially if a casing if used. While a solvent in the form of a liquid or vapor and adjacent the RF dipole antenna 34 may be used to provide cooling, the solvent is typically superheated, for example, having a temperature of greater than 60° C. for propane dependent on local pressure conditions. Additional cooling may be desired.
The dielectric cooling liquid source 23 includes a dielectric cooling liquid supply 27 and a heat exchanger 25. The dielectric cooling liquid source 23 also includes a pump 26 coupled to the dielectric cooling liquid supply 27 and the heat exchanger 25. In particular, as the dielectric cooling liquid, which may be mineral oil, for example, is circulated by way of the pump 26 through the cooling passageways 32a, 32b, heat generated from the RF power may be dissipated within the dielectric cooling, for example, depending on the fluid used for a given implementation. The heat exchanger 25 removes heat from the dielectric cooling liquid as it flows from the subterranean formation 21. Thus, a reduced temperature dielectric liquid e.g., mineral oil, may remove heat from the RF transmission line 33 while RF power is being applied to the hydrocarbon resources. Other types of dielectric cooling liquids may be circulated, for example, a solvent, which may be delivered downhole via the cooling passageways 32a, 32b. Of course, other devices or parts of the RF applicator 30 may be cooled by dielectric cooling liquid.
At least one property of the dielectric cooling liquid, a flow rate of the dielectric cooling liquid, and a configuration of the cooling passageways cooperate to generate a turbulent flow of the dielectric cooling liquid adjacent surfaces of the concentric tubular conductors 31a, 31b. For example, the properties of the dielectric cooling liquid that may cooperate may include a density and a viscosity. A turbulent flow enhances thermal transfer. In other words, the turbulent flow removes an increased amount of heat from adjacent the surfaces of the concentric tubular conductors 31a, 31b. Of course, generating a turbulent flow may be particularly useful for other devices or elements part of or associated with the RF applicator, which may or may not be within the wellbore 24.
The turbulent flow may have a Reynolds number greater than 2500, for example. A Reynolds number is defined where a fluid is in relative motion to a surface and typically is based upon the fluid, i.e., dielectric cooling liquid, properties of density and viscosity, plus a velocity and a characteristic length or characteristic dimension. A Reynolds number Re may be defined as follows:
where:
For the flow in the concentric tubular conductors 31a, 31b, the Reynolds number is generally defined as:
where:
In the present embodiment, in particularly, for the annular or concentric tubular conductors 31a, 31b, the hydraulic diameter can be shown algebraically to reduce to
D
H,annulus
=D
0
−D
i
The turbulent flow provides an increased diametral temperature change for practical lengths and heat loading. For relatively long lengths, a practical inlet to outlet temperature delta tends to drive the desired flow. A relatively small diametral temperature variation may increase the reliability of controlling, via measurement, the inlet and outlet temperatures.
Referring to the graph 40 in
Referring now to
The Graetz number, is a dimensionless number that characterizes laminar flow in a conduit. The Graetz number is defined as:
where:
The Graetz number is particularly useful in determining the thermally developing flow entrance length in liquid passageways. For example, a Graetz number of approximately 1000 or less (inverse Graetz number of greater than 0.001) is the point at which a flow would be considered thermally fully developed.
Referring now to
A third coaxial tubular conductor 31c″ surrounds and is spaced from the outer conductor 31b″ and defines a third cooling passageway 32c″ (second coaxial annulus). An RF dipole antenna element 31d″ in the form of tubular conductor surrounds and is spaced apart from the third coaxial tubular conductor 31c″.
A balun tube 31e″ also in the form of a tubular conductor surrounds and is spaced apart from the third coaxial tubular conductor 31c″. A tubular dielectric spacer 37c″ is between the balun tube 31e″ and the RF dipole antenna element 31d″ so that, together, the tubular dielectric spacer, the balun tube and the RF dipole antenna element define a fourth cooling passageway 32d″ (coaxial-balun annulus). A tubular casing 31f″ surrounds and is spaced apart from the tubular dielectric spacer 37″, the balun tube 31e″ and the RF dipole antenna element 31d″ and defines a fifth cooling passageway 32e″ (tube-casing annulus).
Each of the cooling passageways 31a″-31e″ may have a different cooling fluid flowing therethrough. In one embodiment, above the subterranean formation, the apparatus 20″ includes a dielectric cooling liquid source 23″. The dielectric cooling liquid source 23″ includes a dielectric cooling liquid supply 27″ for the RF applicator, a heat exchanger 25″, and a pump 27″ coupled to dielectric cooling liquid supply and the heat exchanger. A dielectric cooling liquid processor 45″ is also coupled to the pump and may filter, desiccate, and/or purify the dielectric cooling liquid. An optional solvent supply may also be coupled to one or more of the cooling passageways 32a″-32e″. A casing cooling fluid source 46 and a balun cooling fluid source 47 may also be coupled to respective cooling passageways, for example, the fifth and fourth cooling passageways 32e″, 32d″, respectively. The casing cooling liquid source 46″ and balun cooling liquid source 47″ each may include a respective liquid supply, a pump, and a heat exchanger similar to the dielectric cooling liquid source 23″. Of course, other liquids and/or liquid configurations may be used. Moreover, the liquids may be pressurized at a pressure greater than the ambient pressure to reduce contaminant intrusion, for example.
The dielectric cooling liquid may provide increased cooling and reduce high voltage breakdown. Balun fluids also reduce high voltage breakdown, provide an increased heat transfer path, and may provide remote tuning and relatively low circulation for contamination removal. The casing cooling fluid reduces high voltage breakdown and provides cooling via natural or forced convection, for example.
The present embodiments, advantageously, by way of a turbulent flow, increase heat removal from the RF applicator 30 to maintain the temperature of the RF transmission line 33, for example, the outer conductor 31b at or below a desired temperature. Natural convection or laminar flow is advantageously used in, for example, the outermost concentric tubular conductor (annulus) to provide an additional layer of control of the temperature of an outer wall of an outermost concentric tubular conductor, to reduce total fluid recirculation to maintain acceptable assembly component temperatures.
A method aspect is directed to a method of processing hydrocarbon resources in a subterranean formation 21 using an apparatus 20 that includes a radio frequency (RF) source 22, a dielectric cooling liquid source 23, and an RF applicator 30 in the subterranean formation and coupled to the RF source to supply RF power to the hydrocarbon resources. The RF applicator 30 includes concentric tubular conductors 31a, 31b defining cooling passageways 32a, 32b therebetween coupled to the dielectric cooling fluid source 23.
The method includes generating a turbulent flow of the dielectric cooling liquid adjacent surfaces of the concentric tubular conductors 31a, 31b to thereby enhance thermal transfer. The turbulent flow may be generated to have a Reynolds number of greater than 2500, for example. To generate the turbulent flow, the variables that are used to determine the Reynolds number may be adjusted or configured. In particular, the method includes configuring at least one property of the dielectric cooling liquid, e.g., the viscosity and density. The properties of the dielectric cooling liquid may be chosen by choosing a dielectric cooling liquid with the desired properties. The method also includes configuring a flow rate of the dielectric cooling liquid. The flow rate may be configured by operation of the pump 26, for example. The turbulent flow is also generated by at least configuring the cooling passageways, for example, the diameters and cross-sectional areas of the concentric tubular conductors 31a, 31b. Where, for example, dielectric spacers 37′ are used, the turbulent flow may further be generated by configuring the openings 22a′-22d′ so that an inverse of the Graetz number is less than 0.05.
Many modifications and other embodiments of the invention will also come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
