Patent Publication Number: US-2021189837-A1

Title: Erosion control system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 16/173,732, filed Oct. 29, 2018, entitled “Erosion Control System,” which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates generally to hydrocarbon extraction systems. 
     BACKGROUND 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Wells are drilled to extract resources, such as oil and gas, from subterranean reserves. These resources can be difficult to extract because they may flow relatively slowly to the well bore. Frequently, a substantial portion of the resource is separated from the well by bodies of rock and other solid materials. These solid formations impede fluid flow to the well and tend to reduce the well&#39;s rate of production. 
     In order to release more oil and gas from the formation, the well may be hydraulically fractured. Hydraulic fracturing involves pumping a frac fluid that contains a combination of water, chemicals, and proppant (e.g., sand, ceramics) into a well at high pressures. The high pressures of the fluid increases crack size and crack propagation through the rock formation, which releases more oil and gas, while the proppant prevents the cracks from closing once the fluid is depressurized. Unfortunately, the high-pressures and abrasive nature of the frac fluid may wear components. 
     BRIEF DESCRIPTION 
     In one embodiment, a hydrocarbon extraction system that includes an erosion control system. The erosion control system includes a housing defining a first inlet, a second inlet, and an outlet. The housing receives and directs a flow of a particulate laden fluid between the first inlet and the outlet. A conduit rests within the housing. The conduit changes a direction of the particulate laden fluid and reduces erosion of the housing. The conduit is inserted into the housing through the second inlet. The conduit defines a plurality of apertures between an exterior surface and an interior surface of the conduit. The apertures direct the fluid into a conduit cavity. The conduit guides the fluid entering the conduit cavity to the outlet. The erosion control system excludes a plug and/or a sleeve around or in the conduit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a block diagram of an embodiment of a hydrocarbon extraction system; 
         FIG. 2  is a cross-sectional perspective view of an embodiment of an erosion control system; 
         FIG. 3  is a partial cross-sectional view of an embodiment of an erosion control system; 
         FIG. 4  is a partial cross-sectional view of an embodiment of an erosion control system; 
         FIG. 5  is a partial cross-sectional view of an embodiment of an erosion control system; 
         FIG. 6  is a partial cross-sectional view of an embodiment of a conduit of an erosion control system; and 
         FIG. 7  is a partial cross-sectional view of an embodiment of a conduit of an erosion control system. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” “said,” and the like, are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” “having,” and the like are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, the use of “top,” “bottom,” “above,” “below,” and variations of these terms is made for convenience, but does not require any particular orientation of the components. 
     The present embodiments disclose an erosion control system that reduces erosion of the pipes and other components of a mineral extraction system by an erosive fluid while changing a flow direction of the erosive fluid. The erosive fluid may be a frac fluid, oil carrying particulate (e.g., sediment, rock), among others. Because these fluids flow at high velocities with abrasive materials they may increase wear on hydrocarbon extraction system components as the fluid flow path changes the fluid flow direction. As will be explained below, the erosion control system includes a housing that defines a cavity. A conduit with apertures is placed within the cavity. In operation, the erosive fluid flows through an inlet in the housing and through the apertures in the conduit. The conduit changes the flow direction of the erosive fluid and directs the erosive fluid to an outlet in the housing. The conduit may also reduce turbulence as the fluid flows through the housing by controlling the fluid flow direction. By controlling how the erosive fluid flows through the housing with the conduit, the erosion control system may reduce erosion/wear of the housing. It should be understood that the erosion control system may be used in systems other than mineral extraction systems. 
       FIG. 1  is a block diagram that illustrates an embodiment of a hydrocarbon extraction system  10  capable of hydraulically fracturing a well  12  to extract various minerals and natural resources (e.g., oil and/or natural gas). The hydrocarbon extraction system  10  includes a frac tree  14  coupled to the well  12  via a wellhead hub  16 . The wellhead hub  16  generally includes a large diameter hub disposed at the termination of a well bore  18  and is designed to connect the frac tree  14  to the well  12 . The frac tree  14  may include multiple components that enable and control fluid flow into and out of the well  12 . For example, the frac tree  14  may route oil and natural gas from the well  12 , regulate pressure in the well  12 , and inject chemicals into the well  12 . 
     The well  12  may have multiple oil and/or gas formations  20  at different locations. In order to access each of these formations (e.g., hydraulically fracture), the hydrocarbon extraction system may use a downhole tool coupled to a tubing (e.g., coiled tubing, conveyance tubing). In operation, the tubing pushes and pulls the downhole tool through the well  12  to align the downhole tool with each of the formations  20 . Once the tool is in position, the tool prepares the formation to be hydraulically fractured by plugging the well  12  and boring through the casing  22 . For example, the tubing may carry a pressurized cutting fluid that exits the downhole tool through cutting ports. After boring through the casing, the hydrocarbon extraction system  10  pumps frac fluid  24  (e.g., a combination of water, proppant, and chemicals) into the well  12 . 
     As the frac fluid  24  pressurizes the well  12 , the frac fluid  24  fractures the formations  20  releasing oil and/or natural gas by propagating and increasing the size of cracks  26 . Once the formation  20  is hydraulically fractured, the hydrocarbon extraction system  10  depressurizes the well  12  by reducing the pressure of the frac fluid  24  and/or releasing frac fluid  24  through valves (e.g., wing valves). 
     The frac tree  14  includes valves  28  and  30  that couple to a frac head or housing  32  at a first inlet  34 . These valves  28  and  30  fluidly couple to pumps that pressurize and drive the frac fluid into the well  12 . In some embodiments, the valves  28  and  30  may be gate valves. To facilitate insertion of tools into the well  12 , the fracturing tree or frac tree  14  may include a lubricator  36  coupled to the frac head or housing  32 . The lubricator  36  is an assembly with a conduit that enables tools to be inserted into the well  12 . These tools may include logging tools, perforating guns, among others. For example, a perforating gun may be placed in the lubricator  36  for insertion in the well  12 . After performing downhole operations (e.g., perforating the casing), the tool is withdrawn back into the lubricator  36  with a wireline. In order to block the flow of frac fluid into the lubricator  36  while fracing the well  12 , the frac tree  14  includes one or more valves  38 , such as gate valves. 
     As illustrated, as the frac fluid  24  flows through the housing  32 , the housing  32  changes the flow path direction of the frac fluid  24 . In  FIG. 1  the change is ninety degrees; however, it should be understood that the change in direction (i.e., angle) may vary depending on the embodiment. The change in the flow path may increase wear of the housing  32  as particulate repeatedly contacts sections of the housing  32 . In order to reduce wear on the housing  32 , the hydrocarbon extraction system  10  includes the erosion control system  40 . The erosion control system  40  includes the housing  32  and a conduit  42  (e.g., cage) placed within the housing  32 . As will be explained below, the conduit  42  receives the frac fluid  24  (e.g., erosive fluid) flowing through the housing  32  and redirects the frac fluid  24  to reduce wear on the housing  32 . As the frac fluid  24  flows into and through the conduit  42 , the conduit  42  may reduce turbulence of the frac fluid  24 . 
       FIG. 2  is a cross-sectional perspective view of an embodiment of an erosion control system  40 . As explained above, the erosion control system  40  includes the housing  32 . The housing  32  defines an inlet  60  and an outlet  62  and a flow path  64  between the inlet  60  and the outlet  62 . In operation, fluid flows through the housing  32  between the inlet  60  and the outlet  62 . However, because of the significant change in direction of the flow path  64  between the inlet  60  and the outlet  62  (e.g., ninety degree bend), an erosive fluid may create undesirable wear on the housing  32 . For example, erosive fluid may erode the bend or corner  66  in the housing  32 . 
     In order to redirect the flow of erosive fluid away from the corner  66  and/or other portions of the housing  32 , the erosion control system  40  includes the conduit  42  (e.g., cage). The conduit  42  rests within a cavity  68  defined by the housing  32  and receives the fluid through apertures  70  into a conduit cavity  72 . The conduit  42  then directs the fluid flow through the conduit cavity  72  to the outlet  62 . In some embodiments, the volume of the cavity  68  is at least 1.5 times greater than the volume of the portion of the conduit  42  within the cavity  68 . This difference in volume enables the housing  32  to reduce the velocity of the fluid within the cavity  68  and thus reduce the velocity of the fluid before it enters and flows through the apertures  70 . Reducing the velocity of the fluid may reduce erosion of the housing  32  and/or the conduit  42 . The apertures  70  may be circular, rectangular, semi-circular, etc. 
     The conduit  42  is inserted into the housing  32  through a second inlet  74 . A bonnet  76  may couple to the housing  32  with fasteners  78  over the second inlet  74  in order to retain the conduit  42  within the housing  32 . Over time the flow of erosive fluid through the housing  32  and conduit  42  may erode the conduit  42 . When this occurs, the conduit  42  may be removed and replaced with another conduit. By replacing the conduit  42 , the erosion control system  40  may increase the life of the housing  32  and reduce operating costs. It should be noted that the erosion control system  40  excludes a sleeve and/or plug for opening and closing the apertures  70  in the conduit  42 . The apertures  70  are therefore always open and able to transfer fluid between the inlet  60  and the outlet  62 . 
     The apertures  70  extend about the circumference of the conduit  42  and along a longitudinal axis  80  of the conduit  42 . In some embodiments, the apertures  70  may be centered on an axis  80  of a first flow passage  84  that extends between the inlet  60  and the cavity  68 . In some embodiments, the apertures  70  may be offset from the axis  80  of the first flow passage  84 . In  FIG. 2 , the conduit  42  includes two rows of apertures  70  that extend about the circumference of the conduit  42 . However, it should be understood that other embodiments may include different numbers of rows, such as 1, 2, 3, 4, 5, or more. In some embodiments, the size of the apertures and number of apertures may differ between rows. In some embodiments, the spacing between rows may also differ. For example, some rows may be placed closer together. In some embodiments, the apertures  70  may also be arranged to facilitate hydrodynamic energy dissipation. For example, the apertures  70  may be arranged in pairs so that each aperture  70  is aligned with and offset from a corresponding aperture  70  by one-hundred eighty degrees. In operation, fluid flow (e.g., fluid jets) through these pairs of apertures  70  contacts each other in the conduit cavity  72  dissipating/reducing the energy of the fluid before it flows out of the conduit  42 . 
     In some embodiments, the erosion control system  40  may include seals  82  and  84  (e.g. circumferential elastomeric seals) that rest in corresponding grooves on the conduit  42  and/or in the housing  32 . The seals  82  and  84  form seals between the housing  32  and the conduit  42 , which may reduce erosion of the housing  32  by blocking fluid flow from bypassing the apertures  70  in the conduit  42 . 
       FIG. 3  is a partial cross-sectional view of an embodiment of an erosion control system  110 . The erosion control system  110  includes a housing  112  (e.g., frac head, goat head) with multiple flow passages. For example the housing  112  may include a first flow passage  114 , a second flow passage  116 , and a third flow passage  118  (i.e., behind the conduit  122 ). It should be understood that the housing  112  may include numbers of flow passages (e.g., 1, 2, 3, 4, 5, 6, or more). The flow passages  114 ,  116 , and  118  direct fluid flow to the cavity  120  containing the conduit  122 . Like the discussion above, the conduit  122  reduces wear/erosion on housing  112  by forcing the fluid to flow through the conduit  122 . For example, the conduit  122  may reduce undesirable wear around the surface  124  (e.g., bend, edge) proximate the outlet flow passage  126  created by the change in fluid flow direction through the housing  112 . 
     In order to redirect the flow of erosive fluid away from the surface  124 , the conduit  122  defines apertures  128  that receive the fluid. As the fluid flows through the apertures  128  the conduit  122  directs the fluid flow through the conduit cavity  130  to the outlet  132 . In some embodiments, the volume of the cavity  120  is at least 1.5 times greater than the volume of the conduit  122  within the cavity  120  in order to reduce the velocity of the fluid and thus wear. 
     The conduit  122  is inserted into the housing  112  through an inlet  134  and into a passage  136 . During insertion of the conduit  122 , a first end  138  of the conduit  122  passes through the passage  136  and through the cavity  120  before contacting and resting in a counterbore  140 . In operation, the counterbore  140  enables the housing  112  to retain the conduit  122  in position within the housing  112 . More specifically, the counterbore  140  enables the housing  112  to block and/or reduce movement of the conduit  122  in directions  142  and  144 . The counterbore  104  may also properly position the apertures  128  within the cavity  120 , or in other words offset the apertures  128  a desired distance  146  from the surface  124 . 
     As illustrated, the first end  138  defines a first diameter  148  that is smaller than a second diameter  150  of a second end  152  of the conduit  122 . The difference between the diameters  148  and  150  may facilitate insertion of the first end  138  into the housing  112  and thus placement of the conduit  122  within the housing  112  by enabling the first end  138  to easily pass through the passage  136 . 
     The conduit  122  forms a seal with the housing  112  with one or more seals  154  (e.g. circumferential elastomeric seals) that rest in corresponding grooves on the conduit  122  and/or in the housing  112 . Both the first and second ends  138  and  152  include one or more seals  154  that enable the first end  138  to form a seal with the counterbore  140  and a seal between the second end  152  and the passage  136 . The seals  154  may reduce erosion of the housing  112  by blocking fluid flow from bypassing the apertures  128  in the conduit  122 . 
     The apertures  128  extend about the circumference of the conduit  122  and along a longitudinal axis  156  of the conduit  122 . In  FIG. 3 , the conduit  122  includes five rows of apertures  128  that extend about the circumference of the conduit  122 . However, it should be understood that other embodiments may include different numbers of rows, such as 1, 2, 3, 4, 5, 10, or more. In some embodiments, the apertures  128  may be arranged to facilitate hydrodynamic energy dissipation. For example, the apertures  128  may be arranged in pairs so that each aperture  128  is aligned with and offset from a corresponding aperture  128  by one-hundred eighty degrees (as illustrated with lines  158 ). In operation, fluid flow (e.g., fluid jets) through these pairs of apertures  128  contacts each other in the conduit cavity  130  dissipating/reducing the energy of the fluid before flowing out of the conduit  122 . 
     While not illustrated, a bonnet or other piece of equipment (e.g., spool, valve) may couple to the housing  112  in order to retain the conduit  122  within the housing  112 . Over time the flow of erosive fluid through the housing  112  and conduit  122  may erode the conduit  122 . When this occurs, the conduit  122  may be removed and replaced with another conduit. In this way, the erosion control system  110  may increase the life of housing  112 , which may reduce operating costs. Again, the erosion control system  40  excludes a sleeve and/or plug for opening and closing the apertures  128  in the conduit  122 . The apertures  128  are therefore always open enabling fluid to flow through the conduit  122 . In addition, the conduit  122  may reduce turbulence of the fluid as it flows through the housing  112 . 
       FIG. 4  is a partial cross-sectional view of an embodiment of an erosion control system  180 . The erosion control system  180  includes a housing  182  with first and second flow inlet passages  184 ,  186 . It should be understood that the housing  182  may include additional flow passages (e.g., 3, 4, 5, 6, or more). The flow passages  184  and  186  direct fluid flow to respective cavities  238  and  240 . Positioned within these respective cavities  238  and  240  are first and second conduits  192  and  194 . Like the discussion above, the conduits  192  and  194  reduce wear/erosion on the housing  182  by forcing the fluid to flow through one or both of the conduits  192 ,  194 . For example, the conduit  192  may reduce undesirable wear around the surface  196  (e.g., bend, edge) defining the outlet  198  and around the surface  200  defining the outlet  202 . 
     In order to redirect the flow of erosive fluid away from the surfaces  196  and  200 , the conduits  192  and  194  define respective apertures  204  and  206  that receive the fluid. As the fluid flows through the apertures  204  and  206  the conduits  192  and  194  direct the fluid flow to an outlet  208  in the housing  182 . As illustrated, the first and second conduits  192  and  194  are in fluid communication. Accordingly, fluid flow through the first conduit  192  will flow through the second conduit  194  before exiting the housing  182  or vice versa. Similar to the discussion above, the volume of the cavities  238  and  240  is at least 1.5 times greater than the volume of the portions of the respective conduits  192 ,  194  within the cavities  238 ,  240  in order to reduce fluid velocity. 
     As illustrated, the conduit  192  is inserted through inlet  210  and into a passage  212 . The conduit  192  passes through the passage  212  and through the cavity  238  before contacting and resting in a counterbore  214 . The counterbore  214  enables the housing  182  to retain the conduit  192  in position within the housing  182 . The conduit  194  is inserted through the outlet  208  and into the passage  212 . The conduit  194  passes through the passage  212  and through the cavity  240  before contacting and resting in a counterbore  216 . The counterbore  216  enables the housing  182  to retain the conduit  194  in position within the housing  182 . The conduits  192  and  194  seal with the housing  182  with one or more seals  218  (e.g. circumferential elastomeric seals) that rest in corresponding grooves on the conduits  192  and  194  and/or the housing  182 . 
     The apertures  204  and  206  extend about the circumferences of the respective conduits  192  and  194 . In  FIG. 4 , the conduits  192  and  194  include three rows of apertures. However, it should be understood that other embodiments may include different numbers of rows, such as 1, 2, 3, 4, 5, 10, or more. The number, size, and/or rows of apertures may differ between the conduits  192  and  194  with one of the conduits defining more apertures, differently sized apertures, and/or more rows of apertures. The apertures  204  and  206  may also be arranged to facilitate hydrodynamic energy dissipation as discussed above. 
     While not illustrated, bonnets or other pieces of equipment (e.g., spool, valve) may couple to the housing  182  in order to retain the conduit  192  and  194  within the housing  182 . Over time the flow of erosive fluid through the housing  182  may erode the conduits  192  and  194 . When this occurs, the conduits  192  and  194  may be removed and replaced. In this way, the erosion control system  180  may increase the life of housing  182 , which may reduce operating costs. The erosion control system  180  excludes sleeves and/or plugs for opening and closing the apertures  204  and  206  in the respective conduits  192  and  194 . The apertures  204  and  206  are therefore always open to fluid flow through the housing  182 . 
       FIG. 5  is a partial cross-sectional view of an embodiment of an erosion control system  230 . The erosion control system  230  includes a housing  232  with first and second inlet flow passages  234 ,  236 . It should be understood that the housing  232  may include additional flow passages (e.g., 3, 4, 5, 6, or more). The inlet flow passages  234  and  236  direct fluid flow to respective cavities  238  and  240 . Positioned within these respective cavities  238  and  240  is a conduit  242 . The conduit  242  reduces wear/erosion on the housing  232  by forcing the fluid to flow through first and second sets of apertures  250  and  252 . For example, the conduit  242  may reduce undesirable wear around the surface  246  (e.g., bend, edge) that defines the cavity  238  and around the surface  248  that defines the cavity  240 . 
     After flowing through the apertures  250  and  252 , the conduit  242  directs the fluid to an outlet  254  in the housing  232 . As illustrated, the conduit  242  is inserted into a passage  256  through an inlet  258  in the housing  232 . The conduit  242  seals with the housing with one or more seals  260  (e.g. circumferential elastomeric seals) that rest in corresponding grooves. 
     The sets of apertures  250  and  252  extend about the circumferences of the conduit  242 . As illustrated, the sets of apertures  250  and  252  are positioned within the respective cavities  240  and  242  to receive fluid flow through the inlet passages  234  and  236 . The sets of apertures  250  and  252  include three rows of apertures. However, other embodiments may include different numbers of rows, such as 1, 2, 3, 4, 5, 10, or more. The number of apertures, aperture rows, and/or aperture sizes may differ between the sets of apertures  250  and  252 . For example one of the sets of apertures  250  or  252  may include more apertures and/or more rows of apertures. The sets of apertures  250  and  252  may also be arranged to facilitate hydrodynamic energy dissipation as discussed above. 
     While not illustrated, a bonnet or another piece of equipment (e.g., spool, valve) may couple to the housing  232  in order to retain the conduit  242  within the housing  232 . Over time the flow of erosive fluid through the housing  232  may erode the conduit  242 . When this occurs, the conduit  242  may be removed and replaced. In this way, the erosion control system  230  may increase the life of housing  232 . The erosion control system  230  excludes a sleeve and/or plug for opening and closing the sets of apertures  250  and  252  in the conduit  242 . 
       FIG. 6  is a partial cross-sectional view of a conduit  280  (e.g., conduits  42 ,  122 ,  192 ,  194 ,  242 ) that forms part of an erosion control system (e.g., erosion control system  40 ,  110 ,  180 ,  230 ). As illustrated, the conduit  280  includes a plurality apertures  282 . The apertures  282  enable a fluid to enter a conduit cavity  284 . The conduit cavity  284  fluidly communicates with an outlet of the erosion control system enabling the conduit  280  to change a flow direction of a fluid. In some embodiments, the conduit  280  may include inserts  286  (e.g., wear inserts) that are placed within one or more of the apertures  282 . The inserts  286  define respective apertures  288  that fluidly communicate with the conduit cavity  284 . In some embodiments, the inserts  286  may be made out of a material that is tougher than the material of the conduit  280 . For example, the inserts  286  may be made out of polycrystalline diamond, cubic boron nitride, ceramic, tungsten carbide, hardened tool steels, nitrided alloy steels, hardened stainless steels, among others. In operation, these inserts  286  resist erosion of the conduit  280  as an erosive fluid flows through the apertures  282 . 
       FIG. 7  is a partial cross-sectional view of a conduit  300  (e.g., conduits  42 ,  122 ,  192 ,  194 ,  242 ) that forms part of an erosion control system (e.g., erosion control system  40 ,  110 ,  180 ,  230 ). As illustrated, the conduit  300  includes a plurality apertures  302 . The apertures  302  enable a fluid to enter a conduit cavity  304 . The conduit cavity  304  fluidly communicates with an outlet of the erosion control system. In some embodiments, the conduit  300  may be formed out of a plurality of layers  306  (e.g., 2, 3, 4, 5, or more). As illustrated, the conduit  300  includes a first layer  308  (e.g., outer layer) and a second layer  310  (e.g., inner layer). These layers  306  may be formed from different materials. For example, the first layer  308  may be formed from a softer and/or more ductile material (e.g., low alloy steel, tempered stainless steels, aged stainless steels, tempered alloy steels), while the second layer  310  may be formed from a tougher and/or more abrasion resistant material (e.g., nitride steel, tungsten carbide, hardened stainless steels, hardened tool steels, nitrided alloy steels, ceramics). A softer and/or more ductile material for the first layer  308  may enable the conduit  300  to withstand impacts from material in the fluid flow (e.g., rock) passing through the erosion control system. A tougher and/or abrasion resistant material for the second layer  310  may enable the conduit  300  to resist wear as an abrasive fluid flow enters the apertures  302  and flows through the conduit  300 . In some embodiments, the first layer  308  may be formed from a tough and/or more abrasion resistant material, while the second layer  310  may be formed from a softer and/or more ductile material. By forming the conduit  300  out of different layers of material, the conduit  300  may resist wear while changing the direction of a fluid flowing through an erosion control system. 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.