Abstract:
A hydrodynamic pulse tool and method for cleaning, stimulation and production enhancement of oil, gas and injection wells by propagating successive pressure waves through the wellbore and/or the producing/injecting formation in a directional or vectored manner. The tool comprises a resonance chamber defined by a generally cylindrical hollow tubular member adapted for connection to conventional coiled or jointed tubing, and at least one hydraulically driven pulse generator rotatably disposed within the resonance chamber. The hydraulic force of pressurized fluid pumped through the tool drives the rotation of the at least one pulse generator, which generates successive sequential hydraulic pressure pulses in a sequential, sequential offsetting and/or sequential reinforcing manner.

Description:
TECHNICAL FIELD 
       [0001]    The presently described subject matter relates to apparatus and methods for the cleaning, stimulation, and production enhancement of oil, gas and injection wells. 
       BACKGROUND 
       [0002]    Sonic pulse tools that emit pressure waves to vibrate/pulse fluids and solids within the production formation of a petroleum or gas production well are commonly used in the oilfield industry to stimulate production or injection enhancement. Without restriction to a theory, it is believed that the propagation of pressure waves through the production or injection formation may cause the vibration at the molecular level of fluids and solids within the producing/injection zone, and that this in turn assists in the mobilization and production of fluids. Molecular vibration may also result in one or more of the following beneficial effects: repair and removal of naturally occurring or man-made formation damage; suspension of wellbore damage in suspension fluid; removal of scale, filter cake, wax, asphaltenes, bitumen or other materials; increasing reservoir connectivity, injectivity and production; selective enhancement of stimulation fluid; and decreasing viscosity of heavy oil to facilitate mobilization. Sonic pulse tools may also be used to facilitate the cleaning of the wellbore itself, or of individual production, injection or casing string components thereof. 
         [0003]    By way of example, U.S. Pat. No. 8,069,914 describes a hydraulic actuated pump system that may include a sonic pulse tool comprising a hydraulic coupling or resonance assembly that generates pulsed pressure waves, which are emitted into a formation production zone through a plurality of jet members. The pressure waves propagate radially outward from the pulse tool through the formation, in some embodiments up to about 12 feet, and together with the venturi effect created by the action of the jet members generate a radial “push/pull” type of positive/negative pressure face at the formation to mobilize production fluids into the wellbore. The wave frequency is determined by the number of pulses per second, which can be used to calculate the wavelength being exerted on the production formation. The pressure or flowrate at which hydraulic fluid is injected through the sonic pulse tool determines the amplitude or power of the pressure waves. 
         [0004]    U.S. patent publication no. US 2010/0290313 describes downhole pulse stimulation tools comprising a resonance chamber defining at least one pulse emitting opening, and a pulse generator that is either rotatably disposed within the resonance chamber and directly or indirectly rotated by the wellbore rod string, or that is slidingly disposed within the resonance chamber and directly or indirectly reciprocated by the rod string. The pulse generator defines at least one pulse generating opening that periodically aligns with the at least one pulse emitting opening as the pulse generator cycles within the resonance chamber housing. The fluid pressure within the pulse generator is at a higher pressure than the outside pressure due to pump action, so a pulse of fluid pressure is emitted outward from the resonance chamber with each cycle of the pulse stimulation tool. 
         [0005]    As with the sonic pulse tools described in U.S. Pat. No. 8,069,914 and other prior-known pulse stimulation tools, each pressure pulse generated by the pulse stimulation tools of U.S. 2010/0290313 is emitted generally simultaneously through each of the plurality of pulse emitting openings (or jets) that are provided. In some embodiments of U.S. 2010/0290313, paired upper and lower pulse emitting openings generate two sequential pulses for each rotation of the single pulse generator. Nevertheless, in such embodiments, each sequential pulse continues to comprise a simultaneous pulse from each of the upper and lower pluralities of pulse emitting openings. 
         [0006]    The pressure waves that are generated within a producing formation by prior-known pulse stimulation tools accordingly propagate outward from the tool in a generally radial “push/pull” positive/negative, but non-directional manner. 
       SUMMARY 
       [0007]    Improvements in the cleaning, stimulation and/or production enhancement of a hydrocarbon production or injection well may be achieved by propagating successive pressure waves through the wellbore and/or the producing/injecting formation in a directional or vectored manner. The presently described subject matter is accordingly directed to hydrodynamic pulse tools and methods that generate sequential hydraulic pressure pulses that propagate pressure waves radially outward along successively different directional vectors. In some embodiments, sequential offsetting and/or reinforcing pressure pulses may also be generated. 
         [0008]    In preferred embodiments, a hydrodynamic pulse tool comprises a resonance chamber defined by a generally cylindrical hollow tubular member adapted for connection to conventional coiled or jointed tubing, and at least one hydraulically driven pulse generator rotatably disposed within the resonance chamber. The hydraulic force of pressurized fluid pumped through the tool is employed to drive the rotation of the at least one pulse generator substantially about the longitudinal axis of the tubular resonance chamber. 
         [0009]    The inner profile of the generally tubular resonance chamber may in some embodiments define one or more internal flanges or seats for retaining or limiting the longitudinal travel of the at least one pulse generator within the resonance chamber, and in some embodiments these flanges or seats may further include a taper that corresponds with an outside taper of the pulse generator. In some applications, annular bushings or bearings may also be used to facilitate the rotation and/or the longitudinal location of the at least one pulse generator within the resonance chamber. 
         [0010]    In preferred embodiments, each of the at least one pulse generators of the tool comprises a generally cylindrical member with a central longitudinal bore. The outside diameter of at least a portion of each pulse generator comprises a zone that is dimensioned for rotational sliding fit within the resonance chamber, and a plurality of tangential jets extend through the annular body of the pulse generator tangentially from the central longitudinal bore surface to the outside radial surface of the pulse generator within the zone. In preferred embodiments, the tangential jets extend in an orientation that is substantially perpendicular to the longitudinal axis of the pulse generator and the tool. 
         [0011]    The resonance chamber further comprises a plurality of spaced-apart pulse emitting outlets positioned to correspond with the tangential jets of the pulse generator, and through which pressurized fluid may exit the tool to create a hydraulic pressure pulse. At least one of the tangential jets is in fluid communication with a corresponding one of the plurality of pulse emitting outlets provided in the resonance chamber at any one time. As pressurized fluid passes through a tangential jet that is in fluid communication with a corresponding pulse emitting outlet, fluid pressure acts on a wall surface of the pulse emitting outlet and the reactionary force thereby created causes rotation of the pulse generator. The release of the pressurized fluid through the pulse emitting outlet also creates a pressure pulse that propagates a pressure wave through the wellbore and/or the producing/injection formation. 
         [0012]    To sustain the rotational drive of the at least one pulse generator during use, the tangential jets of the pulse generator and the pulse emitting outlets of the resonance chamber are suitably oriented and dimensioned to provide a selected limited degree of overlap, such that fluid communication between a subsequent tangential jet/emitting outlet pairing is initiated just before the rotation of the pulse generator closes off the fluid communication between a current tangential jet/emitting outlet paring. Accordingly, apart from this required but limited overlap, only one tangential jet of each pulse generator (or, in the case of a “multi-level” hydrodynamic pulse tool, one tangential jet of each level—see, below) is substantially in fluid communication with a pulse emitting outlet at any one time. The degree of overlap that may be necessary to sustain rotational drive of the at least one pulse generator is dependent in part upon the pressure and viscosity of the fluid being pumped through the tool. In most embodiments, the cross-sectional dimensions of the pulse emitting outlets are larger than those of the tangential jets. 
         [0013]    In order to generate sequential hydraulic pressure pulses that cause the propagation of pressure waves along successively different directional vectors (as opposed to the generally radial “push/pull” positive/negative, but non-directional propagation of pressure waves of prior-known devices) while sustaining rotational drive, in embodiments of the tool that employ a single one-level pulse generator, the resonance chamber comprises at least three pulse emitting outlets and the pulse generator comprises at least four corresponding tangential jets. In such a configuration, which may be designated a “3:4 tool” configuration, each of the three pulse emitting outlets are oriented about the radial periphery of the resonance chamber and spaced apart at roughly 120° intervals relative to the longitudinal axis of the resonance chamber, and each of the four tangential jets are spaced apart at roughly 90° intervals relative to the longitudinal axis of the pulse generator. As the pulse generator is rotated by the hydraulic force of the pressurized fluid, the pressurized fluid is sequentially released through each of the three pulse emitting outlets, thereby generating sequential hydraulic pressure pulses that propagate pressure waves radially outward at 0°, 120° and 240° vectors relative to the longitudinal axis of the tool. 
         [0014]    Similar preferred single pulse generator embodiments include “4:5 tool” and “5:6 tool” configurations, in which sequential hydraulic pressure pulses propagate sequential pressure waves radially outward at 0°, 90°, 180° and 270° vectors (in the case of a “4:5 tool”), and at 0°, 72°, 144°, 216° and 288° vectors (in the case of a “5:6 tool”) respectively relative to the longitudinal axis of the tool. Single generator pulse stimulation tools in accordance with embodiments of the present subject matter may theoretically be provided in any ratio of “n” pulse emitting outlets to “n+1” tangential jets, but for tools that are adapted for connection to conventional coiled or jointed tubing, size and manufacturing constraints typically limit the upper ratio to tools with a configuration of about “7:8”. 
         [0015]    In other preferred embodiments comprising a single pulse generator, the tangential jets and the corresponding pulse emitting outlets are arranged in two or more discrete levels along the longitudinal axis of the tool to provide a “multi-level” single pulse generator hydrodynamic pulse tool. In one such multi-level tool embodiment, which may be designated a “double 3:4 tool”, the upper level of pulse emitting outlets comprises three outlets that are spaced apart by 120° relative to one another about the longitudinal axis of the resonance chamber and the lower level of pulse emitting outlets similarly comprises three pulse emitting outlets that are also spaced apart by 120° relative to one another about the longitudinal axis of the resonance chamber, but that are out of phase with the outlets of the upper level by about 60°. In combination, this “double-deck” multi-level single pulse generator embodiment accordingly comprises a single pulse emitting outlet at roughly every 60° about the longitudinal axis of the tool. The single pulse generator of this embodiment comprises two sets of four tangential jets, each set of four being spaced apart at 90° intervals relative to the longitudinal axis of the pulse generator (for a total of eight tangential jets, four corresponding to the upper level of pulse emitting outlets and the other four corresponding to the lower level of pulse emitting outlets). The two sets of four tangential jets may be in phase or “aligned”, such that each of the four tangential jets of the upper level is located directly in line longitudinally above a corresponding one of the four tangential jets of the lower level, or the two sets of four tangential jets may alternatively be out of phase by a selected angle such as 60°. 
         [0016]    If the two sets of tangential jets of this “double 3:4 tool” embodiment are aligned, then as the pulse generator is driven by the pressurized fluid, the tool will sequentially propagate offsetting pressure waves radially outward along simultaneous 0° and 180°; 120° and 300°; and 60° and 240° vectors relative to the longitudinal axis of the tool. Conversely, if the two sets of tangential jets of this embodiment are out of phase by 60°, then as the pulse generator is driven by the pressurized fluid, the tool will sequentially propagate reinforcing pressure waves along simultaneous 0°, 60°, 180° and 240°; followed by 0°, 120°, 180° and 300°; and then 60°, 120°, 240° and 300° vectors relative to the longitudinal axis of the tool. 
         [0017]    As will be readily apparent to those of skill in the art from an appreciation of the present disclosure, numerous other degrees of phase shift or “offset” between the upper and lower levels of pulse emitting outlets and/or between the tangential jets, as well as other tool configurations (such as “double 4:5 tools”, “double 5:6 tools”, etc.) may also be selected to provide further alternate embodiments that generate pressure pulses to propagate pressure waves radially outward along, for example, sequential 0°, 60°, 120°, 180°, 240° and 300° vectors, or along offsetting 0° and 180° vectors alternating with 90° and 270° vectors. 
         [0018]    By way of example, in one family of “double-deck” single pulse generator embodiments that may be designated “double 4:5 tools”, the upper level of pulse emitting outlets comprises four outlets that are spaced apart by 90° relative to one another about the longitudinal axis of the tool and the lower level of pulse emitting outlets similarly comprises four pulse emitting outlets that are also spaced apart by 90° relative to one another about the longitudinal axis of the tool. In one such embodiment, the upper and lower sets of pulse emitting outlets are longitudinally aligned so that twin pulse emitting outlets (one upper outlet and one lower outlet) are positioned at every 90° about the longitudinal axis of the tool. The single multi-level pulse generator of this embodiment comprises two sets of five tangential jets, each set of five being spaced apart at 72° intervals relative to the longitudinal axis of the pulse generator (for a total of ten tangential jets, five corresponding to the upper level of pulse emitting outlets and the other five corresponding to the lower level of pulse emitting outlets), and in which the upper and lower sets of tangential jets are either aligned or out of phase by a selected angle such as 45°. It will also be readily apparent to those of skill in the art from an appreciation of the present disclosure that numerous other single multi-level pulse generator embodiments comprising, for example, three or more levels of jets and corresponding outlets (such as “triple 3:4 tools”, “triple 4:5 tools”, “quadruple 4:5 tools”, etc.) may also be provided. 
         [0019]    Further alternate embodiments that are within the scope of the presently disclosed subject matter include multiple independent pulse generator embodiments, in which two or more individual pulse generators (as opposed to a single pulse generator) are driven independently or in unison within a single resonance chamber to propagate sequential, offsetting and/or reinforcing pressure waves along successively different directional vectors. Yet further alternate embodiments within the scope of the presently disclosed subject matter comprise multiple independent pulse generators in which two or more individual pulse generators are driven independently or in unison within two or more individual resonance chambers to generate sequential, offsetting and/or reinforcing hydraulic pressure pulses that propagate pressure waves radially outward along successively different directional vectors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    For a fuller understanding of the nature and advantages of the disclosed subject matter, as well as the preferred mode of use thereof, reference should be made to the following detailed description read in conjunction with the accompanying simplified drawings. The drawings are not necessarily to scale, with the emphasis instead being placed upon the principles of the disclosed subject matter. The drawings are intended to be illustrative, and therefore should not be used to limit the scope of the disclosed subject matter. In the following drawings, like reference numerals designate like or similar parts or steps. 
           [0021]      FIG. 1  is a schematic perspective view of a hydrodynamic pulse tool in accordance with an embodiment of the presently disclosed subject matter. 
           [0022]      FIG. 2  is a front elevational view of the hydrodynamic pulse tool of  FIG. 1 . 
           [0023]      FIG. 3  is a front elevational cage line view of the hydrodynamic pulse tool of  FIG. 1 . 
           [0024]      FIG. 4  is a front elevational cage line view of the pulse generator of the hydrodynamic pulse tool of  FIG. 1 . 
           [0025]      FIG. 5  is schematic perspective view of a hydrodynamic pulse tool in accordance with another embodiment of the presently disclosed subject matter. 
           [0026]      FIG. 6  is a front elevational view of the hydrodynamic pulse tool of  FIG. 5 . 
           [0027]      FIG. 7  is a top plan cage line view of a “3:4 tool” hydrodynamic pulse tool in accordance with an embodiment of the presently disclosed subject matter. 
           [0028]      FIG. 8  is a top plan cage line view of a “4:5 tool” hydrodynamic pulse tool in accordance with an embodiment of the presently disclosed subject matter. 
           [0029]      FIG. 9  is a schematic perspective view of a representative downhole assembly comprising a hydrodynamic pulse tool in accordance with an embodiment of the presently disclosed subject matter. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    With reference to  FIGS. 1 to 4 , there is illustrated a hydrodynamic pulse tool  10  in accordance with an embodiment of the presently disclosed subject matter. Pulse tool  10  generally comprises cylindrical hollow resonance chamber  12  having upper  14  and lower  16  ends adapted respectively for connection to conventional coiled or jointed tubing, or other conventional downhole well elements (not shown), such as by conventional threaded connection recognized and accepted in the oilfield industry. Rotatably disposed within resonance chamber  12  is single one-level pulse generator  18 . Both the resonance chamber  12  and the pulse generator  18  may be constructed of  4140  steel or other materials suitable for downhole applications, the selection of which is within the ordinary knowledge of those of skill in the art. 
         [0031]    Resonance chamber  12  further comprises a plurality of spaced-apart pulse emitting outlets  20  and, in the illustrated embodiment, a lower flange  22  for limiting downward longitudinal travel of pulse generator  18  within the resonance chamber  12 . Pulse generator  18  further comprises outside taper  24  for rotational sliding contact with flange  22 . In other embodiments, annular bushings or bearings (not shown) may be disposed between flange  22  and outside taper  24 . 
         [0032]    Pulse generator  18  further comprises zone  26  having an outside diameter dimensioned for rotational sliding fit within the resonance chamber  12 , and a central longitudinal bore  28  extending therethrough. A plurality of tangential jets  30 , two of which are illustrated in  FIG. 1  as tangential gets  30   a  and  30   b  respectively, extend through the annular body of the pulse generator  18  tangentially from the surface of central longitudinal bore  28  to the outside radial surface of the pulse generator within the zone  26 . As best seen in  FIGS. 2 and 3 , pulse emitting outlets  20  of resonance chamber  12  have a cross-sectional dimension that is larger than that of tangential jets  30 , and are positioned to sequentially correspond with tangential jets  30  as pulse generator  18  rotates within resonance chamber  12 . 
         [0033]    Pressurized fluid (indicated by arrow A in  FIG. 1 ) is pumped through the hydrodynamic pulse tool  10  to drive the rotation of pulse generator  18  substantially about the longitudinal axis of the resonance chamber  12 . As pressurized fluid passes through a given tangential jet  30  that is in fluid communication with a corresponding pulse emitting outlet  20  (as best seen in  FIG. 2 ), fluid pressure acts on a wall surface  32  of the pulse emitting outlet  20  and the reactionary force thereby created causes rotation of the pulse generator  18 . The release of the pressurized fluid through the tangential jet  30  and thence through pulse emitting outlet  20  also creates a pressure pulse that propagates a pressure wave through the wellbore and/or the producing/injection formation in the vicinity of hydrodynamic pulse tool  10 . The rotational sliding fit between zone  26  of the pulse generator  18  and the resonance chamber  12  substantially prevents bypass of pressurized fluid directly between the cylindrical hollow resonance chamber  12  and the pulse emitting outlets  20 . 
         [0034]    As best understood with reference to  FIGS. 1 ,  7  and  8 , to sustain the rotational drive of the pulse generator  18  during use, tangential jets  30  and pulse emitting outlets  20  are oriented and dimensioned to provide a selected limited degree of overlap, such that fluid communication between a subsequent tangential jet/emitting outlet pairing ( 30   a  and  20  respectively in  FIG. 1 ) is initiated just before the rotation of the pulse generator  18  closes off the fluid communication between a current tangential jet/emitting outlet paring ( 30   b  and  20  respectively in  FIG. 1 ). Accordingly, apart from this required but limited overlap, only one tangential jet  30  of each pulse generator  18  is substantially in fluid communication with a pulse emitting outlet  20  at any one time. The degree of overlap that may be necessary to sustain rotational drive of pulse generator  18  is dependent in part upon the pressure and viscosity of the fluid being pumped through the tool, and the calculation thereof is within the ordinary skill of those in the art. 
         [0035]      FIGS. 1 through 4  illustrate a single one-level pulse generator  18 , and  FIGS. 5 and 6  illustrate an alternate embodiment comprising a single multi-level pulse generator  40  (discussed in further detail below). In order to generate sequential hydraulic pressure pulses that cause the propagation of pressure waves along successively different directional vectors (as opposed to the generally radial “push/pull” positive/negative, but non-directional propagation of pressure waves of prior-known devices) while sustaining rotational drive of a single one-level pulse generator  18  during use, the resonance chamber  12  comprises at least three pulse emitting outlets  20  and the pulse generator  18  comprises at least four corresponding tangential jets  30 . In such a configuration, which may be designated a “3:4 tool” configuration, each of the three pulse emitting outlets  20  are oriented about the radial periphery of the resonance chamber  12  and spaced apart at roughly 120° intervals relative to the longitudinal axis of the resonance chamber  12 , and each of the four tangential jets  30  are spaced apart at roughly 90° intervals relative to the longitudinal axis of the pulse generator  18  (see  FIG. 7 ). As the pulse generator  18  is rotated by the hydraulic force of the pressurized fluid, the pressurized fluid is sequentially released through each of the three pulse emitting outlets  20 , thereby generating sequential hydraulic pressure pulses that propagate pressure waves radially outward at 0°, 120° and 240° vectors relative to the longitudinal axis of the tool  10 . 
         [0036]    Referring now to  FIG. 8 , there are illustrated in top plan cage line view a “4:5 tool” embodiment of a hydrodynamic pulse tool  50  from which sequential hydraulic pressure pulses propagate sequential pressure waves radially outward at 0°, 90°, 180° and 270° vectors. Apart from the number and size of the pulse emitting outlets and tangential jets, the structure of tool  50  is essentially parallel to that of tool  10  described above with reference to  FIGS. 1-4  and  7 . As seen in  FIG. 8 , tool  50  comprises resonance chamber  52  having four pulse emitting outlets  54  oriented about the radial periphery of the resonance chamber  52  and spaced apart at roughly 90° intervals relative to the longitudinal axis of the resonance chamber  52 . As pulse generator  56  is rotated by the hydraulic force of the pressurized fluid, the pressurized fluid is sequentially released through each of the five tangential jets  58  and the four pulse emitting outlets  54 , thereby generating sequential hydraulic pressure pulses that propagate pressure waves radially outward at 0°, 90°, 180° and 270° vectors relative to the longitudinal axis of the tool  50 . 
         [0037]    Returning again to  FIGS. 5 and 6 , a multi-level single pulse generator hydrodynamic pulse tool  40  is illustrated. As shown, multi-level single pulse generator tool  40  comprises a resonance chamber  41  with two opposing upper pulse emitting outlets  42  (one shown in  FIG. 6 ), and two opposing lower pulse emitting outlets  43  (both shown in  FIG. 5 ). Opposing pairs of pulse emitting outlets  42  and  43  are out of phase by 90°, so in combination, the illustrated “double-deck” multi-level single pulse generator tool  40  comprises a single pulse emitting outlet at roughly every 90° about the longitudinal axis of the tool  40 . As best seen in  FIG. 5 , tool  40  further comprises pulse generator  44  with three upper tangential jets  45  and three lower tangential jets  46 . Each of the three upper tangential jets  45  and each of the three lower tangential jets  46  are spaced apart at roughly 120° intervals relative to the longitudinal axis of the pulse generator  40 , and the upper and lower sets of tangential jets  45 ,  46  are out of phase by roughly 60° such that, in combination, the pulse generator  44  comprises a tangential jet at roughly every 60° about the longitudinal axis of the pulse generator  44 . Accordingly, as the pulse generator  44  is driven by the pressurized fluid in use, the tool  40  will sequentially propagate pressure waves radially outward along 0°, 90°; 180° and 270° vectors relative to the longitudinal axis of the tool  40 . 
         [0038]      FIG. 9  illustrates a schematic perspective view of a representative downhole assembly comprising a hydrodynamic pulse tool in accordance with embodiments of the presently disclosed subject matter. Downhole assembly  60  comprises a hydrodynamic pulse tool  62  that may be constructed in accordance with any of the pulse tool embodiments described above with reference to any of the preceding Figures. However, for ease of reference, pulse tool  62  is described in the following discussion in relation to the embodiment of  FIGS. 1-4 . Pulse tool  62  is connected such as by conventional thread means at its lower end  16  to a section of cylindrical tube  64 , and at the opposite end of tube  64  is similarly connected a tip portion  66  of a conventional well entry guide system that has a bevelled development to allow ease of access into well bores that may have inset or upset applications within the primary well bore itself (such as packer restrictions, profile nipples, etc. . . . ). Cylindrical tube  64  may or may not comprise “reflective focusing chambers” of conventional form and construction to provide an entry/exit point for fluid or fluid/gas, and/or to allow a pulse to enter and respectively exit the reflective focusing chambers. 
         [0039]    Pulse tool  62  may similarly be connected such as by conventional thread means at its upper end  14  to a further cylindrical tube  68  that may again comprise reflective focusing chambers of conventional form and construction. If present, these upper reflective focusing chambers are typically oriented in the opposite manner relative to the lower reflective focusing chambers. A conventional jetted top  70  having an angle of declination away from the main central axis of downhole assembly  60  may optionally also be connected to the opposite end of tube  68  and used to facilitate downward thrust while providing for the appropriate removal of solids from around the assembly  60  to be evacuated from the well bore. The entire downhole assembly  60  may be connected such as by thread means to coiled or jointed tubing in a conventional manner. 
         [0040]    The present description includes the best presently contemplated mode of carrying out the subject matter disclosed and claimed herein. While specific terminology may have been used herein, other equivalent features and functions are intended to be included. The description is made for the purpose of illustrating the general principles of the subject matter and not be taken in a limiting sense; the claimed subject matter can find utility in a variety of implementations without departing from the scope of the invention made, as will be apparent to those of skill in the art from an understanding of the principles that underlie the invention.