Hydrocarbon resource recovery apparatus including RF transmission line and associated methods

An apparatus for hydrocarbon resource recovery from a subterranean formation includes a radio frequency (RF) source, an RF antenna to be positioned within the subterranean formation to deliver RF power to the hydrocarbon resource within the subterranean formation, and an RF transmission line extending between the RF source and the RF antenna. The RF transmission line may include RF transmission line sections coupled together in end-to-end relation. Each section may include an inner conductor, an outer conductor surrounding the inner conductor, and an outer load-carrying tubular member surrounding the outer conductor. A respective coupling assembly joins ends of adjacent sections together. Each coupling assembly may include an electrical coupler being fixedly connected to first ends of corresponding inner and outer conductors and being slidably connected to opposing second ends of adjacent inner and outer conductors, and a mechanical coupler connecting ends of adjacent load-bearing tubular members together.

FIELD OF THE INVENTION

The present invention relates to the field of radio frequency (RF) equipment, and, more particularly, to an RF transmission line, such as, for hydrocarbon resource recovery using RF heating and related methods.

BACKGROUND

To recover a hydrocarbon resource from a subterranean formation, wellbore casings or pipes are typically coupled together in end-to-end relation within the subterranean formation. The wellbore casings are generally rigid and often times made of steel. In order to more efficiently recover a hydrocarbon resource from the subterranean formation, it may be desirable to apply radio frequency (RF) power to the subterranean formation within (or adjacent to) the hydrocarbon resource.

For example, U.S. Pat. No. 8,616,273 to Trautman, et al. and U.S. Pat. No. 8,960,291 to Parsche, which are both assigned to Harris Corporation of Melbourne, Fla., the assignee of the present application, disclose a method of heating a petroleum ore by applying RF energy to a mixture of petroleum ore.

As an example of improvements to RF transmission lines, U.S. Pat. No. 8,847,711 to Wright et al., assigned to the assignee of the present application, discloses a series of rigid coaxial sections coupled together in end-to-end relation for use in hydrocarbon resource recovery. Each rigid coaxial section includes an inner conductor and a rigid outer conductor surrounding the inner conductor. Each of the rigid outer conductors includes a rigid outer layer having opposing threaded ends defining overlapping mechanical threaded joints with adjacent rigid outer layers.

U.S. Pat. No. 8,960,272 to Wright et al., also assigned to the assignee of the present application, discloses an RF apparatus for hydrocarbon resource recovery that includes a series of tubular conductors. Each of the tubular conductors may have threads at opposing ends. In addition, the RF apparatus may include bendable tubular dielectric couplers that rotationally interlock opposing ends of the tubular conductors to define a tubular antenna.

To apply the RF energy to the hydrocarbon resource, a rigid coaxial feed arrangement or RF transmission line may be desired to couple to an antenna in the subterranean formation. Typical commercial designs of a rigid coaxial feed arrangement are not generally designed for structural loading or subterranean use, as installation generally requires long runs of the transmission line along the lines of 500-1500 meters. In addition, the transmission line is subjected to significant compressive and tensile loads from thermal expansion and the physical weight of the components of the transmission line.

As an example, a typical overhead transmission line may be capable of 1,000 lbs tension, while it may be desirable for a downhole RF transmission line to have 150,000 to 500,000 lbs tensile capability, which may amount to 150 to 500 times the capacity of an existing commercial product.

In addition, the commercial rigid coaxial designs may be bulky, and require multiple nuts, bolts, washers, and other fasteners to hold the coaxial sections together. Further, larger diameter coaxial sections may limit subterranean uses and a lower profile increases high voltage margins, while reducing antennae bore diameter and wellbore size requirements.

Further improvements to hydrocarbon resource recovery and RF transmission lines may be desirable. For example, it may be desirable to increase the efficiency of assembling a high strength RF transmission line that can withstand relatively high stresses associated with hydrocarbon resource recovery in a subterranean formation.

SUMMARY

In view of the foregoing background, it is therefore an object of the present invention to increase the efficiency of assembling a high strength RF transmission line that can withstand the relatively high stresses associated with hydrocarbon resource recovery in a subterranean formation.

This and other objects, features, and advantages in accordance with embodiments of the invention are provided by an apparatus for hydrocarbon resource recovery from a subterranean formation that may include an RF source, an RF antenna to be positioned within the subterranean formation to deliver RF power to the hydrocarbon resource within the subterranean formation, and an RF transmission line extending between the RF source and the RF antenna. The RF transmission line may include a plurality of RF transmission line sections coupled together in end-to-end relation. Each RF transmission line section may include an inner conductor, an outer conductor surrounding the inner conductor, and an outer load-carrying tubular member surrounding the outer conductor. A respective coupling assembly may join opposing ends of adjacent sections together. Each coupling assembly may include an electrical coupler being fixedly connected to first ends of opposing inner and outer conductors; and being slidably connected to second ends of corresponding inner and outer conductors, and a mechanical coupler connecting opposing ends of adjacent load-bearing tubular members together.

Another aspect is directed to a method for making an RF transmission line to be coupled between an RF source and an RF antenna within a subterranean formation to deliver RF power to a hydrocarbon resource within the subterranean formation. The method may include providing a plurality of RF transmission line sections to be coupled together in end-to-end relation with each RF transmission line section comprising an inner conductor, an outer conductor surrounding the inner conductor, and an outer load-carrying tubular member surrounding the outer conductor. In addition, the method may include using a respective coupling assembly to join opposing ends of adjacent sections together. Each coupling assembly may include an electrical coupler fixedly connected to first ends of corresponding inner and outer conductors and being slidably connected to second ends of opposing inner and outer conductors, and a mechanical coupler connecting opposing ends of adjacent load-bearing tubular members together.

DETAILED DESCRIPTION

Effective pressure balancing of cooling fluid pumped through the coaxial feed is essential to minimizing cost of copper transmission lines by allowing thin wall tubular. Also, decoupling thermal stresses from thin wall transmission line is highly desirable.

It may thus be desirable to provide a high strength RF transmission line for use in a subterranean formation. More particularly, it may be desirable to provide a high strength RF transmission line that includes efficient non-threaded connections for fragile inner and outer conductors but uses standard connections for the tubular, which can withstand relatively high stresses associated with hydrocarbon resource recovery in a subterranean formation. To address this, one approach uses a tubular with inner and outer conductors carried therein, where the tubular assumes the installation and operational loads rather than the inner and outer conductors.

Referring initially toFIG. 1, a radio frequency (RF) transmission line108is positioned within a wellbore112in a subterranean formation102. The subterranean formation102includes hydrocarbon resources105. The wellbore112is illustratively in the form of a vertically extending wellbore112, for example, as may be particularly advantageous for use with RF assisted hydrocarbon resource recovery techniques. Of course, more than one wellbore112and RF transmission line108may be used, and/or other techniques for hydrocarbon resource recovery may be used, for example, the steam assisted gravity drainage (SAGD) hydrocarbon resource recovery technique. A separate producer well could be positioned below the wellbore112. The wellbore112could also be horizontal in other embodiments.

The RF transmission line108is coupled to an RF source104and cooling fluid source107, which are positioned at the wellhead above the subterranean formation102. The RF source104cooperates with the RF transmission line108to transmit RF energy from the RF source104to within the subterranean formation102and the hydrocarbon resources105, for example, for heating the subterranean formation102. An antenna106is coupled to the RF transmission line108within the wellbore112. The RF transmission line108includes a series of RF transmission line sections110a,110b, for example, each on the order of forty feet in length, coupled together in end-to-end relation.

Referring now toFIG. 2, a perspective fragmentary view of the RF transmission line sections110a,110bis provided. The RF transmission line sections110a,110binclude a respective inner conductor114a,114b, an outer conductor116a,116bsurrounding the respective inner conductor114a,114b, and an outer load-carrying tubular member118a,118bsurrounds the respective outer conductor116a,116b. The RF transmission line sections110a,110balso include coupling assemblies120a,120bfor joining opposing ends of adjacent RF transmission line sections together. Mechanical couplers124a,124bof the coupling assemblies120a,120bmay be used to connect opposing ends of adjacent load-bearing tubular members together as described below.

At least one outer spacer156a,156bis carried by an interior of the respective outer load-bearing tubular member118a,118band supporting the respective outer conductor116a,116b, where the outer spacer156a,156bincludes fluid passageways therethrough connected to the cooling fluid source107. Similarly, at least one inner spacer158a,158bis carried by an interior of the respective outer conductor116a,116band supporting the respective inner conductor114a,114b, where the respective inner spacer158a,158bincludes fluid passageways also connected to the cooling fluid source107. The path of the cooling fluid may flow from the cooling fluid source107through the inner114a,114band outer conductors116a,116band back towards the cooling fluid source107(FIG. 1) via a return passageway defined between the tubular118a,118band the outer conductors116a,116b. Pressure balancing with cooling fluid on both sides of the inner114a,114band outer conductors116a,116breduces copper wall thickness allowing for access to deeper reservoirs of hydrocarbon resources105(FIG. 1).

The outer load-carrying tubular members118a,118bmay be a wellbore casing, which may be available from any number of manufacturers. For example, the outer load-carrying tubular member118a,118bmay be steel or stainless steel, and may be a GRANT PRIDECO wellbore casing available from National Oilwell Varco of Houston, Tex., or an ATLAS BRADFORD wellbore casing available from Tenaris S.A. of Liuxembourg. Advantageously, the outer load-carrying tubular members118a,118bof the RF transmission line108(FIG. 1) may be formed using a commercial off the shelf (COTS) tubular or well pipe, for example. Additionally, the coupling arrangement between adjacent outer load-carrying tubular members118a,118bmay include an exterior interrupt arrangement, a flush interrupt arrangement, a semi-flush interrupt arrangement, or a pin-box-pin arrangement, for example. Of course, other coupling arrangements may be used.

More particularly, the outer load-carrying tubular members118a,118bmay have an outer diameter of 5 inches, a maximum tensile strength of 546,787 lbs, and a maximum internal pressure of 12,950 psi. The outer load-carrying tubular members118a,118bmay be another type of wellbore casing having different sizes or strength parameters. The outer load-carrying tubular members118a,118b, while being relatively strong, may not be a relatively good conductor compared to copper, for example.

Each coupling assembly120a,120bof the apparatus may include a respective electrical coupler122a,122bbeing fixedly connected to first ends of corresponding inner114aand respective outer conductors116aand being slidably connected to opposing second ends of adjacent inner114band outer conductors116b. Some elements of the electrical couplers122a,122bare not shown inFIG. 2for sake of clarity.

Referring now toFIG. 3, the inner conductor114aincludes an open interior defining a fluid passageway160afor receiving a cooling fluid from the cooling fluid source107(FIG. 1), which is in turn connected to the fluid passageway160aof the inner conductor114a. In addition, an intermediate fluid passageway162ais defined between the outer conductor116aand the inner conductor114a, and an outer fluid passageway154ais similarly defined between the outer load-carrying tubular member118aand the outer conductor116afor receiving the cooling fluid from the cooling fluid source107(FIG. 1).

Referring now toFIG. 4, the electrical coupler122aincludes an outer sleeve126a having a respective first end128ato be fixedly connected to the first end of the corresponding outer conductor116a(FIG. 2) and a second end130ato be slidably connected to the second end of the corresponding outer conductor116b(FIG. 2). The electrical coupler12amay also include an outer spacer flange146areceived within the outer load-carrying tubular member118a(FIG. 2) and carrying the electrical coupler122a. The mechanical coupler124a described above captures the corresponding electrical coupler122aat a first end of the corresponding load-bearing tubular member118a(FIG. 2) The inner114aand outer conductors116a(FIG. 2) are supported at one of the outer load-carrying tubular members and are uncoupled from thermal elastic effects of the outer load-carrying tubular members118a,118b(FIG. 2). The outer load-carrying tubular members118a,118b(FIG. 2) can rotate with respect to the inner114a,114band outer conductors116a,116b(FIG. 2) to minimize wear. In addition, welds and solder joints may be eliminated by the use of the electrical couplers122a,122bto electrically couple the inner114a,114band outer conductors116a,116b(FIG. 2) of RF transmission line sections110a,110btogether.

The electrical coupler122amay also include at least one contact ring136awithin the first end128aof the outer sleeve126a. The contact ring136amay include a watchband conductive spring contact and an expansion spring carried thereby. The electrical coupler122amay also include a fluid seal142awithin the first end128aof the outer sleeve126a.

Referring now toFIG. 5, the electrical coupler122aincludes an inner contact132ahaving a first end fixedly connected to the first end of the corresponding inner conductor114aand a second end slidably connected to the opposing second end of the adjacent inner conductor114b. A dielectric spacer134ais received within the outer sleeve126aand supports the inner contact132a. The inner conductor114amay be copper, for example, because of its relatively high conductivity. Of course, the inner conductor114amay be another material, for example, aluminum, nickel, gold, brass, beryllium, or a combination thereof.

Referring now toFIGS. 6 and 7, the coupling assembly120amay include the mechanical coupler124ahaving threads127afor connecting opposing ends of the adjacent load-bearing tubular members118a,118btogether, where each of the outer load-carrying tubular members118a,118bincludes threaded ends125a,125b. Accordingly, the outer load-carrying tubular members118a,118bare coupled together using the mechanical coupler threads127adefining overlapping mechanical threaded joints.

In another particular illustrative embodiment, a method is directed to making an RF transmission line108to be coupled between an RF source104and an RF antenna106within a subterranean formation102to deliver RF power to a hydrocarbon resource105within the subterranean formation102. The method includes forming a plurality of RF transmission line sections110a,110bto be coupled together in end-to-end relation so that each RF transmission line section110a,110bincludes a respective inner conductor114a,114b, an outer conductor116a,116bsurrounding the respective inner conductor, and an outer load-carrying tubular member118a,118bsurrounding the respective outer conductor116a,116b.

The method also includes using a respective coupling assembly120a,120bto join opposing ends of adjacent sections110a,110btogether. As described above, each coupling assembly120a,120bmay include an electrical coupler122a,122bfixedly connected to first ends of corresponding inner114a,114band outer conductors116a,116b, and slidably connected to opposing second ends of adjacent inner114a,114band outer conductors116a,116b. A mechanical coupler124a,124bconnects opposing ends of adjacent load-bearing tubular members118a,118btogether. In addition, the method includes positioning a contact ring136awithin the first end128aof the outer sleeve126adescribed above, and positioning a fluid seal142awithin the first end128aof the outer sleeve126a.

The modular nature of the RF transmission line108offloads weight and expansion, and decouples thermal, structural, and weight stresses from thin wall tubes. Moreover, the loads are independent of total length of the RF transmission line108. Thus, decoupling stresses from the RF transmission line108relieves structural stress and allows for smaller wellbore diameter, which directly affects costs of installation of the RF transmission line108.

Another advantage of the RF transmission line108is that it uses a sliding interface rather than threads between the ends of adjacent inner114a,114band outer conductors116a,116bso that the rig does not require rotation during assembly of the RF transmission line108. Also, visual inspection for coupling the inner114a,114band outer conductors116a,116binto the respective electrical coupler122a,122bis permitted. The sliding interface also reduces part count and complexity, and reduces installation time on the rig, which greatly increases the efficiency of assembling the high strength RF transmission line108and reduces installation costs of the RF transmission line108.

Of course, the RF transmission line embodiments as described herein may have application other than for hydrocarbon resource recovery in a subterranean formation as described above. For example, the RF transmission line may be used in any long transmission line run with a significant amount of power (heat) variations. The transmission line could be strung along towers, up tall buildings or coupled among wellheads hundreds of meters apart. High power runs may heat substantially and the temperatures in certain locations can fluctuate fairly drastically between seasons, and this might account for variations in the ground/support structures moving by isolating the loads. In addition, many modifications and other embodiments of the invention will 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.