Method of heating a hydrocarbon resource including slidably positioning an RF transmission line and related apparatus

A method for heating hydrocarbon resources in a subterranean formation may include positioning a tubular conductor within a wellbore in the subterranean formation and slidably positioning a radio frequency (RF) transmission line within the tubular conductor so that a distal end of the transmission line is electrically coupled to the tubular conductor. The method may also include supplying RF power, via the RF transmission line, to the tubular conductor so that the tubular conductor serves as an RF antenna to heat the hydrocarbon resources in the subterranean formation.

FIELD OF THE INVENTION

The present invention relates to the field of hydrocarbon resource recovery, and, more particularly, to hydrocarbon resource recovery using RF heating.

BACKGROUND OF THE INVENTION

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 tar sands where their viscous nature does not permit conventional oil well production. Estimates are that trillions of barrels of oil reserves may be found in such tar sand formations.

In some instances these tar 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 pay zone 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 so that steam is not produced at the lower producer well and steam trap control is used to the same affect. 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, into the lower producer.

Operating the injection and production wells at approximately reservoir pressure may address the instability problems that adversely affect high-pressure steam processes. SAGD may produce a smooth, even production that can be as high as 70% to 80% of the original oil in place (OOIP) in suitable reservoirs. The SAGD process may be relatively sensitive to shale streaks and other vertical barriers since, as the rock is heated, differential thermal expansion causes fractures in it, allowing steam and fluids to flow through. SAGD may be twice as efficient as the older cyclic steam stimulation (CSS) process.

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, although due to the 2008 economic downturn work on new projects has been deferred, 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, namely 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 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 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 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.

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.

Moreover, despite the existence of systems that utilize RF energy to provide heating, such systems may suffer from inefficiencies as a result of impedance mismatches between the RF source, transmission line, and/or antenna. These mismatches may become particularly acute with increased heating of the subterranean formation.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of the present invention to provide a hydrocarbon resource heating method and apparatus that provides more efficient hydrocarbon resource heating.

This and other objects, features, and advantages in accordance with the present invention are provided by a method for heating hydrocarbon resources in a subterranean formation that includes positioning a tubular conductor within a wellbore in the subterranean formation, and slidably positioning a radio frequency (RF) transmission line within the tubular conductor so that a distal end of the transmission line is electrically coupled to the tubular conductor. The method also includes supplying RF power, via the RF transmission line, to the tubular conductor so that the tubular conductor serves as an RF antenna to heat the hydrocarbon resources in the subterranean formation.

The method may further include slidably removing the RF transmission line after supplying RF power. The method may further include slidably positioning another RF transmission line within the tubular conductor so that a distal end of the another transmission line is electrically coupled to the tubular conductor, for example. Accordingly, the method may advantageous increase hydrocarbon resource heating efficiency, for example, by permitting removal of the RF transmission line and substitution of another RF transmission line for adjustment of impedance as the formation is heated.

The tubular conductor may carry an electrical receptacle therein, and the RF transmission line may carry an electrical plug at the distal end thereof. Slidably positioning the RF transmission line may include slidably positioning the RF transmission line so that the electrical plug engages the electrical receptacle, for example.

Positioning the tubular conductor may include positioning the tubular conductor with a tubular dielectric section therein so that the tubular conductor defines a dipole antenna, for example. Slidably positioning the RF transmission line may include slidably positioning a coaxial RF transmission line.

The method may further include flowing at least one fluid through the tubular conductor. Flowing the at least one fluid may include flowing the at least one fluid to control at least one of a temperature and pressure. Flowing the at least one fluid may include flowing at least one of a dielectric fluid, a solvent, and a hydrocarbon resource.

An apparatus aspect is directed to an apparatus for heating hydrocarbon resources in a subterranean formation having a wellbore therein. The apparatus includes a tubular conductor positioned within the wellbore. The tubular conductor has an electrical receptacle carried therein. A radio frequency (RF) transmission line has an electrical plug carried at a distal end thereof slidably positioned within the tubular conductor so that the electrical plug engages the electrical receptacle. The apparatus also includes an RF power source configured to supply RF power, via the RF transmission line, to the tubular conductor so that the tubular conductor serves as an RF antenna to heat the hydrocarbon resources in the subterranean formation.

DETAILED DESCRIPTION

Referring initially toFIGS. 1 and 2, and with respect to the flow chart80inFIG. 3, an apparatus20and method for heating hydrocarbon resources in a subterranean formation21are described. The subterranean formation21includes a wellbore24therein. The wellbore24illustratively extends laterally within the subterranean formation21. In other embodiments, the wellbore24may be a vertically extending wellbore. Although not shown, in some embodiments a respective second or producing horizontal wellbore may be used below the wellbore24, such as would be found in a SAGD implementation, for the collection of oil, etc., released from the subterranean formation21through RF heating.

Referring additionally toFIGS. 4-6, beginning at Block82, the method includes positioning a tubular conductor30within the wellbore24(Block84). The tubular conductor30may be slidably positioned through an intermediate casing25, for example, in the subterranean formation21extending from the surface. The tubular conductor30may couple to the intermediate casing25via a thermal liner packer26or debris seal packer (DSP), for example. In particular, the intermediate casing25may be a TenarisHydril Wedge 563™ 13⅜″ J55 casing available from Tenaris S.A. of Luxembourg. The tubular conductor30may be a tubular liner, for example, a slotted or flush absolute cartridge system (FACS) liner. In particular, the tubular conductor30may be a TenarisHydril Wedge 532™ 10¾″ stainless steel liner also available from Tenaris S.A. of Luxembourg. Of course either or both of the intermediate casing25and tubular conductor30may be another type of casing or conductor.

The tubular conductor30has a tubular dielectric section31therein so that the tubular conductor defines a dipole antenna. In other words, the tubular dielectric section31defines two tubular conductive segments32a,32beach defining a leg of the dipole antenna. Of course, other types of antennas may be defined by different or other arrangements of the tubular conductor30. The tubular conductor30may also have a second dielectric section35therein defining a balun isolator. The balun isolator35may be adjacent the thermal packer26. Additional dielectric sections may be used to define additional baluns.

The tubular conductor30carries an electrical receptacle33therein. More particularly, the electrical receptacle33includes first and second electrical receptacle contacts34a,34bthat electrically couple, respectively, to the two tubular conductive segments32a,32b. Each of the first and second electrical receptacle contacts34a,34bmay have openings36a,36btherein, respectively, to permit the passage of fluids, as will be explained in further detail below.

At Block86, the method includes slidably positioning a radio frequency (RF) transmission line40within the tubular conductor30so that a distal end41of the RF transmission line is electrically coupled to the tubular conductor. In particular, the RF transmission line40is illustratively a coaxial RF transmission line and includes an inner conductor42surrounded by an outer conductor43. An end cap51couples to the inner conductor42and extends outwardly therefrom. The end cap51may be an extension of the second electrical receptacle contact34b. The inner conductor42may be spaced apart from the outer conductor43by dielectric spacers52. The dielectric spacers52may have openings53therein to permit the passage or flow of fluids, as will be explained in further detail below.

The RF transmission line40carries an electrical plug44at the distal end41to engage the electrical receptacle33. More particularly, the electrical plug44includes first and second electrical plug contacts45a,45belectrically coupled to the inner and outer conductors42,43. The first and second electrical plug contacts45a,45bengage the first and second electrical receptacle contacts34a,34bof the electrical receptacle33.

Each electrical plug contact45a,45bmay include an electrically conductive body48a,48band spring contacts49a,49bthat may deform when compressed or coupled to the first and second electrical receptacle contacts34a,34b. Of course, other or additional types of electrical plugs44and/or coupling techniques may be used. The RF transmission line40at the distal end41may be spaced from the tubular conductor30by dielectric spacers47, for example, bow spring centralizers.

At Block88, the method includes supplying RF power, from an RF source28and via the RF transmission line40, to the tubular conductor30so that the tubular conductor serves as an RF antenna to heat the hydrocarbon resources in the subterranean formation21.

The method may include flowing a fluid through the tubular conductor30(Block90). The fluid may include a dielectric fluid, a solvent, and/or a hydrocarbon resource. For example, the tubular conductor30and the RF transmission line40may be spaced apart to define a fluid passageway55. A solvent may be flowed through the fluid passageway55. In some embodiments, the solvent may be dispersed into the subterranean formation21through openings in the tubular conductor30adjacent the hydrocarbon resources.

In some embodiments, a fluid may be circulated through the RF transmission line40. For example, the inner conductor42may be tubular defining a first fluid passageway56, and the outer conductor43may be spaced apart from the inner conductor to define a second fluid passageway57. A coolant, for example, may be passed through the first fluid passageway56from above the subterranean formation21to the RF antenna, and the coolant may be returned via the second fluid passageway57. Of course, other fluids may be passed through the first and second fluid passageways56,57, and the fluid may not be circulated. In other embodiments, the fluid may be passed through other or additional annuli.

In other embodiments, for example, as illustrated inFIG. 7, an additional casing61′ or annuli, may surround the RF transmission line40′ and define a balun. The additional casing61′ may define a third fluid passageway62′, for example. In some embodiments, the third fluid passageway62′ may be filled with a balun fluid whose level may be adjusted, for example, to match resonate frequency of the balun to the resonate frequency of the RF antenna. For example, as the subterranean formation21′ changes, the frequency may be adjusted, and thus, also the balun. A pressure check valve may be used to return balun fluid via a fluid passageway designated for fluid return. Additional casings may be used to define additional baluns.

A temperature sensor29and/or a pressure sensor27may be positioned in the tubular conductor30, or more particularly, coupled to the RF transmission line40. The fluid may be flowed (Block90) to control the temperature and/or pressure. Other or additional sensors may be positioned in the wellbore24, and the fluid may be flowed to control other parameters.

After supplying RF power to heat the hydrocarbon resources, if, for example, the properties of subterranean formation21or RF antenna changed (i.e., impedance), the RF transmission line40may be slidably removed (Block92). Of course, the RF transmission line40may be removed for any or other reasons.

If, for example, additional heating of the hydrocarbon resources is desired, the method may include slidably positioning another RF transmission line within the tubular conductor30so that a distal end of the another transmission line is electrically coupled to the tubular conductor (Block94). The method ends at Block96.

Indeed, the apparatus20may advantageously support multiple hydrocarbon resource processes, for example, injection of a gas or solvent while RF power is being supplied, producing or recovering hydrocarbon resources while applying RF power, and using a single wellbore for injection and production. Performing these functions, for example, without an additional wellbore, may provide increased cost savings, thus increasing efficiency.

Moreover, the apparatus20allows removal of the RF transmission line40from the wellbore24, and common mode suppression, thus resulting in further cost savings. Also, the RF transmission line impedance may be adjusted during use, which may result in even further cost savings and increased efficiency. For example, at startup (1-2 years) a 50-Ohm RF transmission line may be used. For long term operation (e.g. after 2 years), a 25-30 Ohm RF transmission line may be used.