Patent Publication Number: US-7896070-B2

Title: Providing an expandable sealing element having a slot to receive a sensor array

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. Ser. No. 11/688,089, entitled “Completion System Having a Sand Control Assembly, an Inductive Coupler, and a Sensor Proximate the Sand Control Assembly,” filed Mar. 19, 2007, which claims the benefit under 35 U.S.C. §119(e) of the following provisional patent applications: U.S. Ser. No. 60/787,592, entitled “Method for Placing Sensor Arrays in the Sand Face Completion,” filed Mar. 30, 2006; U.S. Ser. No. 60/745,469, entitled “Method for Placing Flow Control in a Temperature Sensor Array Completion,” filed Apr. 24, 2006; U.S. Ser. No. 60/747,986, entitled “A Method for Providing Measurement System During Sand Control Operation and Then Converting It to Permanent Measurement System,” filed May 23, 2006; U.S. Ser. No. 60/865,084, entitled “Welded, Purged and Pressure Tested Permanent Downhole Cable and Sensor Array,” filed Nov. 9, 2006; U.S. Ser. No. 60/866,622, entitled “Method for Placing Sensor Arrays in the Sand Face Completion,” filed Nov. 21, 2006; U.S. Ser. No. 60/867,276, entitled “Method for Smart Well,” filed Nov. 27, 2006 and U.S. Ser. No. 60/890,630, entitled “Method and Apparatus to Derive Flow Properties Within a Wellbore,” filed Feb. 20, 2007. Each of the above applications is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to providing an expandable sealing element having a slot to receive a sensor array. 
     BACKGROUND 
     A completion system is installed in a well to produce hydrocarbons (or other types of fluids) from reservoirs) adjacent the well, or to inject fluids into the reservoir(s). Sensors are typically installed in completion systems to measure various parameters, including temperature, pressure, and other well parameters that are useful for monitoring the status of the well and the fluids that are flowing in the well. 
     In some scenarios, presence of certain components in the completion system can make deployment of sensors difficult. One such example component is a packer used to seal around a portion of the completion system to isolate zones in the well. In many conventional systems, to allow for deployment of sensors past a sealing packer, a packer is provided with an axial port (which is a feedthrough port extending axially through the packer) to allow a communication line connected to the sensor to be passed through the packer. Typically, the communication line has to be spliced at the ported packer to allow the communication line to pass through the ported packer. However, an issue with splicing the communication line is that maintaining a hermetic seal would not be feasible since the communication line would have to be in separate segments to achieve the splicing. Also, performing splicing at the job site is time consuming and costly. 
     In other conventional configurations, instead of using ported packers, communication lines can be extended through a housing of a completion assembly on which the packer is mounted to avoid interference with the packer. However, such arrangements also add to the complexity and cost of the completion system. 
     SUMMARY 
     In general, according to an embodiment, an apparatus for use in a well includes a completion assembly, and an expandable sealing element provided on the outer surface of the completion assembly. The expandable element has a slot. The apparatus further includes a sensor array. The slot in the expandable sealing element enables the expandable sealing element to expand around the sensor array. 
     Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example arrangement that has a sensor array wound on a spool, where the sensor array can be deployed into a well by unwinding from the spool for attachment to a completion system. 
         FIGS. 2A-2B  illustrate the completion system with expanding sealing elements having slots to receive the sensor array, in accordance with an embodiment. 
         FIG. 3  illustrates the completion system with expanding sealing elements having slots to receive a sensor array that has one or more sensors, according to another embodiment. 
         FIG. 4  illustrates an assembly of a completion system housing segment, a sensor array, and an expandable sealing element having a slot to receive the sensor array, according to an embodiment. 
         FIG. 5  is a cross-sectional view of a portion of the assembly of  FIG. 4 . 
         FIGS. 6A-6C  illustrate a sensor array being received into a slot of an expandable sealing element, according to an embodiment. 
         FIG. 7  shows a two-stage completion system according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. 
     As used here, the terms “above” and “below”; “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or diagonal relationship as appropriate. 
       FIG. 1  illustrates an example arrangement that includes a sensor array  100  for deployment into a well  102 . The sensor array  100  is attached to a completion system  104  for deployment into the well  102 . A sensor array includes a continuous communication line having portions with sensors  106 . The sensor array  100  is “continuous” in the sense that the sensor array provides a continuous seal against external fluids, such as wellbore fluids, along its length. Note that in some embodiments, the continuous sensor array  100  can actually have discrete housing sections that are sealably attached together, such as by welding or by some other sealing mechanism. In other embodiments, the sensor array can be implemented with an integrated, continuous housing formed without breaks. 
     The sensor array  100  has an inner bore that can be hermetically sealed from an external environment. For example, the inner bore of the sensor array  100  can be filled with an inert gas (e.g., argon). 
     The sensor array  100  is wound onto a spool  108 , which is positioned at an earth surface or offshore platform above the well  102 . Initially, the entire length of the sensor array  100  may be wound onto the spool  108 . At the well site, as the completion system  104  is deployed into the wellbore  102 , the sensor array  106  can be unwound and attached to the completion system  104 , with both the combination of the completion system  104  and sensor array  100  inserted into the wellbore  102  together. Such a sensor array that is deployable into a wellbore from a spool is often referred to as a “spoolable sensor array.” 
     The completion system  104 , in the example depicted in  FIG. 1 , has perforated pipe sections  110  to enable flow of fluids between the outside of the completion system  104  (wellbore annulus) and an inner bore of the completion system  104 . In alternative implementations, other types of completion systems  104  can be used. 
     The pipe sections  110  are interconnected by connection mandrels  112 . Expandable sealing elements  114 , such as sealing packers, are arranged on outer surfaces of corresponding connection mandrels  112 . When the completion system  104  is deployed into the wellbore, the sealing elements  114  are initially in an unexpanded, deflated or retracted state such that the sealing elements  114  are withdrawn from an inner surface  116  of the wellbore  102 . This allows for movement of the completion system  104  inside the wellbore  102 . 
     An “expandable sealing element” refers to a sealing element that is enlargeable from a first radial point to a second radial point. One example of an expandable sealing element is a swellable sealing element that swells in response to an activating chemical. Another example of an expandable sealing element is an inflatable sealing element that is inflated by application of fluid pressure. 
     Once the completion system  104  is lowered to a target depth in the wellbore  102 , the sealing elements  114  are activated to expand radially outwardly from the completion system  104  to engage the inner surface  116  of the wellbore  102 . Engagement of the sealing elements  114  against the inner surface  116  of the wellbore allows for a fluid seal to be provided by such engagement. The inner surface  116  of the wellbore can either be a surface of a casing or liner (e.g., that lines the wellbore) or the inner wall of an open (i.e., un-cased or un-lined) wellbore. 
     In alternative implementations, instead of providing a complete seal by engaging the sealing elements  114  against the wellbore surface  116 , partial seals can be provided instead, where the sealing elements  114  expand radially outwardly to constrict or narrow an area of an annular flow path, which can be used to achieve a desired pressure drop for example. 
     As explained further below, in accordance with some embodiments, slots are provided in the sealing elements  114  to receive portions of the sensor array  100 . The slot in each sealing element  114  allows the sealing element  114  to expand outwardly around the sensor array  100  for engagement with the inner surface  116  of the wellbore  102 . Note that the sensor array  100  is sealably received inside the slot of each sealing element  114  such that a fluid seal may be provided between the sensor array  100  and the expandable sealing element  114  when the sealing element  114  is in an expanded state. This allows for proper sealing by each expandable sealing element  114  in the annular region between the completion system  104  and the wellbore  102  such that different zones of the wellbore  102  can be isolated. 
     Note that a slot can be pre-formed in the sealing element  114 , or alternatively, a slot can be formed in the sealing element  114  after deployment of the sealing element into the wellbore. The sealing element can be formed of a material into which a slot can be readily made without preventing the element&#39;s ability to perform its desired function. In this discussion, reference to a “slot” of a sealing element is to either a pre-formed slot or a slot created after deploying the sealing element into the wellbore. 
       FIG. 2A  shows the initial deployment of the completion system  104  and sensor array  100  in the wellbore  102 , in which the expandable sealing elements  114  are in their initial deflated state.  FIG. 2B , on the other hand, shows that the expandable sealing elements  114  have been activated to expand radially outwardly to engage the inner surface  116  of the wellbore  102 . Activation of the sealing elements  114  can be accomplished in one of a number of ways, including activation based on applying fluid pressure, providing an activating chemical to cause the expandable sealing elements  114  to swell, and so forth. As depicted in  FIG. 2B , the expanded sealing elements  114  have sealed around the sensor array  100  and have engaged the wellbore inner surface  116 . As a result, zones  202 ,  204 , and  206  are defined, where each of the zones  202 ,  204 , and  206  is isolated from other portions of the wellbore  102 . 
     Note that within each of the zones  202 ,  204 , and  206 , at least one sensor can be provided. For example, a sensor  106 A is provided in zone  202 , a sensor  106 B is provided in zone  204 , and a sensor  106 C is provided in zone  206 . The respective sensor  106 A,  106 B, or  106 C can be used to measure a property of the corresponding zone  202 ,  204 , or  206 . The measured property can include temperature, pressure, flow rate, fluid property, and so forth. The array of measurements can in turn be used to derive properties or characteristics of the wellbore such as the flow of reservoir fluid into the formation, for example to allocate flow across different producing zones. The data from the permanently installed sensor array can be combined with other reservoir and wellbore information, for example, from logging data that was obtained while drilling the well or obtained during a subsequent intervention. 
     The zones  202 ,  204 , and  206  are adjacent corresponding zones of a reservoir  210  through which the wellbore  102  extends. Fluid (e.g., hydrocarbon, fresh water, etc.) can be produced from the reservoir zones into the corresponding zones  202 ,  204 , and  206 . Alternatively, fluids can be injected into the reservoir  210  through the zones  202 ,  204  and  206 . 
     Although reference has been made to a sensor array in the foregoing discussion, it is noted that, in an alternative embodiment, a similar technique can be applied to a more traditional communications arrangement in which one or more sensors are connected to a communication line. Such an arrangement is depicted in  FIG. 3 , which shows a communication line  300  that has one end connected to one or more sensors  302 . The expandable sealing elements  114  with their respective slots are able to seal around the communication line  300  for engagement with the inner surface  116  of the wellbore. This assembly of the communication line  300  and the one or more sensors  302  may also be referred to as a “sensor array.” 
       FIG. 4  illustrates a portion of an assembly of a connector mandrel  112 , an expandable sealing element  114 , and a sensor array  100  or  300 .  FIG. 5  is a cross-sectional view of the assembly of  FIG. 4 . As depicted, the expandable sealing element  114  is provided on an outer surface  400  of the connector mandrel  112 . A slot  402  is provided in the expandable sealing element  114 . The slot  402  extends in a radial direction in the sealing element  114  from the outermost surface  404  of the sealing element  114  to a point  406  closer to the connector mandrel outer surface  400 . In the axial direction (indicated by X), the slot  402  extends along the length of the expandable sealing element  114 . The sensor array  100  or  300  is received in the slot  402 . The slot  402  has an open end  408  at the outermost surface  404  of the expandable sealing element  114 , where the open end  408  of the slot  402  is able to receive the sensor array  100  or  300  that is initially not received in the slot  402 . 
     Receipt of the sensor array in the slot  402  is depicted in  FIGS. 6A-6C . In  FIG. 6A , the sensor array  100  or  300  is depicted as being outside the expandable sealing element  114  prior to being received in the slot  402 .  FIG. 6B  shows the sensor array  100  or  300  as it is initially received at the open end  408  of the slot  402 .  FIG. 6C  shows the sensor array  100  or  300  received deeper (in the radial direction) into the slot  402 . Effectively, the slot  402  allows the sensor array  100  or  300  to be gradually received deeper into the slot  402  as the sealing element  112  expands. 
     By using a slot  402  that has an open end (end  408 ), a ported packer does not have to be used, since the expandable sealing element  114  can receive the sensor array  100  or  300  and seal around the sensor array  100  or  300  as the sealing element  112  expands. 
     By using techniques according to some embodiments, the expandable sealing elements  114  can be set against impermeable zones of a reservoir through which the wellbore  102  extends. Once set, the expandable sealing elements  114  provide zonal isolation such that flow can be produced from specific reservoir zones to flow within the wellbore. The sensors provided in each of the zones allow for measurement of characteristics associated with the flow. 
     The system according to some embodiments can also be used for reservoir stimulation in which a certain fluid, such as acid, can be pumped between two sealing elements in an isolated zone. 
     The system according to some embodiments can also be used in an injector well, where the sealing elements isolate injected fluids to particular zones of the reservoir. The sensors can be used to measure data so that fluid injection can be optimized. For example, the injection pressure can be monitored to keep it below the pressure that would fracture the rock. 
     A communication line that is part of a sensor array can also be used for deploying optical fibers across a wellbore with packers. In this case, a communication line has an inner axial bore. Once the communication line is deployed downhole, and the sealing elements  114  are expanded to seal around the communication line, an optical fiber can be pumped down the control line and positioned across a desired reservoir without the need for any splicing. The optical fiber can be used for performing distributed temperature sensing (in which the entire length of the optical fiber can be used to determine a temperature profile along the length). Alternatively, the optical fiber can be connected to the sensors. 
     In some embodiments, a completion system having at least two stages (an upper completion section and a lower completion section) is used. The lower completion section is run into the well in a first trip, where the lower completion section includes the sensor assembly. An upper completion section is then run in a second trip, where the upper completion section is able to be inductively coupled to the first completion section to enable communication and power between the sensor assembly and another component that is located uphole of the sensor assembly. The inductive coupling between the upper and lower completion sections is referred to as an inductively coupled wet connect mechanism between the sections. “Wet connect” refers to electrical coupling between different stages (run into the well at different times) of a completion system in the presence of well fluids. The inductively coupled wet connect mechanism between the upper and lower completion sections enables both power and signaling to be established between the sensor assembly and uphole components, such as a component located elsewhere in the wellbore at the earth surface. 
     The term two-stage completion should also be understood to include those completions where additional completion components are run in after the first upper completion, such as commonly used in some cased-hole frac-pack applications. In such wells, inductive coupling may be used between the lowest completion component and the completion component above, or may be used at other interfaces between completion components. A plurality of inductive couplers may also be used in the case that there are multiple interfaces between completion components. 
     Induction is used to indicate transference of a time-changing electromagnetic signal or power that does not rely upon a closed electrical circuit, but instead includes a component that is wireless. For example, if a time-changing current is passed through a coil, then a consequence of the time variation is that an electromagnetic field will be generated in the medium surrounding the coil. If a second coil is placed into that electromagnetic field, then a voltage will be generated on that second coil, which we refer to as the induced voltage. The efficiency of this inductive coupling increases as the coils are placed closer, but this is not a necessary constraint. For example, if time-changing current is passed through a coil is wrapped around a metallic mandrel, then a voltage will be induced on a coil wrapped around that same mandrel at some distance displaced from the first coil. In this way, a single transmitter can be used to power or communicate with multiple sensors along the wellbore. Given enough power, the transmission distance can be very large. For example, solenoidal coils on the surface of the earth can be used to inductively communicate with subterranean coils deep within a wellbore. Also note that the coils do not have to be wrapped as solenoids. Another example of inductive coupling occurs when a coil is wrapped as a toroid around a metal mandrel, and a voltage is induced on a second toroid some distance removed from the first. 
     In alternative embodiments, the sensor assembly can be provided with the upper completion section rather than with the lower completion section. In yet other embodiments, a single-stage completion system can be used. 
     Although reference is made to upper completion sections that are able to provide power to lower completion sections through inductive couplers, it is noted that lower completion sections can obtain power from other sources, such as batteries, or power supplies that harvest power from vibrations (e.g., vibrations in the completion system). Examples of such systems have been described in U.S. Publication No. 2006/0086498. Power supplies that harvest power from vibrations can include a power generator that converts vibrations to power that is then stored in a charge storage device, such as a battery. In the case that the lower completion obtains power from other sources, the inductive coupling will still be used to facilitate communication across the completion components. 
     Reference is made to  FIG. 7  in the ensuing discussion of a two-stage completion system according to an embodiment.  FIG. 7  shows the two-stage completion system with an upper completion section  700  engaged with a lower completion section  702 . 
     As shown in  FIG. 7 , an open hole region is below a lined or cased region that has a liner or a casing  706 . In the open hole region, a portion of the lower completion section  702  is provided proximate to a sand face  708 . 
     To prevent passage of particulate material, such as sand, a sand screen  710  is provided in the lower completion section  702 . Alternatively, other types of sand control assemblies can be used, including slotted or perforated pipes or slotted or perforated liners. A sand control assembly is designed to filter particulates, such as sand, to prevent such particulates from flowing from a surrounding reservoir into a well. 
     In accordance with some embodiments, the lower completion section  702  has a sensor assembly (or array)  712  that has multiple sensors  714  positioned at various discrete locations across the sand face  708 . In some embodiments, the sensor assembly  712  is in the form of a sensor cable (also referred to as a “sensor bridle”). The sensor cable  712  is basically a continuous control line having portions in which sensors  714  are provided. The sensor cable  712  is “continuous” in the sense that the sensor cable provides a continuous seal against fluids, such as wellbore fluids, along its length. Note that in some embodiments, the continuous sensor cable can actually have discrete housing sections that are sealably attached together. In other embodiments, the sensor cable can be implemented with an integrated, continuous housing without breaks. 
     In the lower completion section  702 , the sensor cable  712  is also connected to a controller cartridge  716  that is able to communicate with the sensors  714 . The controller cartridge  716  is able to receive commands from another location (such as at the earth surface or from another location in the well, e.g., from control station  746  in the upper completion section  700 ). These commands can instruct the controller cartridge  716  to cause the sensors  714  to take measurements or send measured data. Also, the controller cartridge  716  is able to store and communicate measurement data from the sensors  714 . Thus, at periodic intervals, or in response to commands, the controller cartridge  716  is able to communicate the measurement data to another component (e.g., control station  746 ) that is located elsewhere in the wellbore or at the earth surface. Generally, the controller cartridge  716  includes a processor and storage. The communication between sensors  714  and control cartridge  716  can be bi-directional or can use a master-slave arrangement. 
     The controller cartridge  716  is electrically connected to a first inductive coupler portion  718  (e.g., a female inductive coupler portion) that is part of the lower completion section  702 . As discussed further below, the first inductive coupler portion  718  allows the lower completion section  702  to electrically communicate with the upper completion section  700  such that commands can be issued to the controller cartridge  716  and the controller cartridge  716  is able to communicate measurement data to the upper completion section  700 . 
     In embodiments in which power is generated or stored locally in the lower completion section, the controller cartridge  716  can include a battery or power supply. 
     As further depicted in  FIG. 7 , the lower completion section  702  includes a packer  720  (e.g., gravel pack packer) that when set seals against casing  706 . The packer  720  isolates an annulus region under the packer  720 , where the annulus region is defined between the outside of the lower completion section  702  and the inner wall of the casing  706  and the sand face  708 . 
     A seal bore assembly  726  extends below the packer  720 , where the seal bore assembly  726  is to sealably receive the upper completion section  700 . The seal bore assembly  726  is further connected to a circulation port assembly  728  that has a slidable sleeve  730  that is slidable to cover or uncover circulating ports of the circulating port assembly  728 . During a gravel pack operation, the sleeve  730  can be moved to an open position to allow gravel slurry to pass from the inner bore  732  of the lower completion section  702  to the annulus region  724  to perform gravel packing of the annulus region  724 . The gravel pack formed in the annulus region  724  is part of the sand control assembly designed to filter particulates. 
     In the example implementation of  FIG. 7 , the lower completion section  702  further includes a mechanical fluid loss control device, e.g., formation isolation valve  734 , which can be implemented as a ball valve. When closed, the ball valve isolates a lower part of the inner bore from the part of the inner bore above the formation isolation valve  734 . When open, the formation isolation valve  734  can provide an open bore to allow flow of fluids as well as passage of intervention tools. Although the lower completion section  702  depicted in the example of  FIG. 7  includes various components, it is noted that in other implementations, some of these components can be omitted or replaced with other components. 
     As depicted in  FIG. 7 , the sensor cable  712  is provided in the annulus region outside the sand screen  710 . By deploying the sensors  714  of the sensor cable  712  outside the sand screen  710 , well control issues and fluid losses can be avoided by using the formation isolation valve  734 . Note that the formation isolation valve  734  can be closed for the purpose of fluid loss control during installation of the two-stage completion system. 
     As depicted in  FIG. 7 , the upper completion section  700  has a straddle seal assembly  740  for sealing engagement inside the seal bore assembly  726  of the lower completion section  702 . The outer diameter of the straddle seal assembly  740  of the upper completion section  700  is slightly smaller than the inner diameter of the seal bore assembly  726  of the lower completion section  702 . This allows the upper completion section straddle seal assembly  740  to sealingly slide into the lower completion section seal bore assembly  726 . In an alternate embodiment the straddle seal assembly can be replaced with a stinger that does not have to seal. 
     Arranged on the outside of the upper completion section straddle seal assembly  740  is a snap latch  742  that allows for engagement with the packer  720  of the lower completion section  702 . When the snap latch  742  is engaged in the packer  720 , as depicted in  FIG. 7 , the upper completion section  700  is securely engaged with the lower completion section  702 . In other implementations, other engagement mechanisms can be employed instead of the snap latch  742 . 
     Proximate to the lower portion of the upper completion section  700  (and more specifically proximate to the lower portion of the straddle seal assembly  740 ) is a second inductive coupler portion  744  (e.g., a male inductive coupler portion). When positioned next to each other, the second inductive coupler portion  744  and first inductive coupler portion  718  (as depicted in  FIG. 7 ) form an inductive coupler that allows for inductively coupled communication of data and power between the upper and lower completion sections. 
     An electrical conductor  747  (or conductors) extends from the second inductive coupler portion  744  to the control station  746 , which includes a processor and a power and telemetry module (to supply power and to communicate signaling with the controller cartridge  716  in the lower completion section  702  through the inductive coupler). The control station  746  can also optionally include sensors, such as temperature and/or pressure sensors. 
     The control station  746  is connected to an electric cable  748  (e.g., a twisted pair electric cable) that extends upwardly to a contraction joint  750  (or length compensation joint). At the contraction joint  750 , the electric cable  748  can be wound in a spiral fashion (to provide a helically wound cable) until the electric cable  748  reaches an upper packer  752  in the upper completion section  700 . The upper packer  752  is a ported packer to allow the electric cable  748  to extend through the packer  752  to above the ported packer  752 . The electric cable  748  can extend from the upper packer  752  all the way to the earth surface (or to another location in the well). 
     In another embodiment, the control station  746  can be omitted, and the electrical cable  748  can run from the second inductive coupler portion  744  (of the upper completion section  700 ) to a control station elsewhere in the well or at the earth surface. 
     The contraction joint  750  is optional and can be omitted in other implementations. The upper completion section  700  also includes a tubing  754 , which can extend all the way to the earth surface. The upper completion section  700  is carried into the well on the tubing  754 . 
     In operation, the lower completion section  702  is run in a first trip into the well and is installed proximate to the open hole section of the well. The packer  720  ( FIG. 2 ) is then set, after which a gravel packing operation can be performed. To perform the gravel packing operation, the circulating port assembly  728  is actuated to an open position to open the port(s) of the circulating port assembly  728 . A gravel slurry is then communicated into the well and through the open port(s) of the circulating port assembly  728  into the annulus region  724 . The annulus region  724  is then filled with slurry until the annulus region  724  is gravel packed. 
     Next, in a second trip, the upper completion section  700  is run into the well and attached to the lower completion section  702 . Once the upper end lower completion sections are engaged, communication between the controller cartridge  716  and the control station  746  can be performed through the inductive coupler that includes the inductive coupler portions  718  and  744 . The control station  746  can send commands to the controller cartridge  716  in the lower completion section  702 , or the control station  746  can receive measurement data collected by the sensors  714  from the controller cartridge  716 . 
     While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.