Abstract:
Method and recharging mechanism for resetting a pressure in a low pressure recipient. The recharging mechanism includes a low pressure recipient configured to have first and second chambers, the first chamber being configured to receive a hydraulic liquid at a high pressure and the second chamber being configured to include a gas at a low pressure. The recharging mechanism further includes a valve fluidly connected to a first port of the first chamber; a pumping device fluidly connected to a second port of the first chamber; and a blowout preventer (BOP) section fluidly connected to the valve and configured to close or open a ram block. The pumping device is configured to evacuate the hydraulic fluid from the first chamber of the low pressure recipient when the valve closes a fluid communication between the first port of the first chamber and the BOP section.

Description:
BACKGROUND 
     1. Technical Field 
     Embodiments of the subject matter disclosed herein generally relate to methods and devices and, more particularly, to mechanisms and techniques for recharging a device that generates a subsea force. 
     2. Discussion of the Background 
     During the past years, with the increase in price of fossil fuels, the interest in developing new production fields has dramatically increased. However, the availability of land-based production fields is limited. Thus, the industry has now extended drilling to offshore locations, which appear to hold a vast amount of fossil fuel. 
     The existing technologies for extracting the fossil fuel from offshore fields may use a system  10  as shown in  FIG. 1 . More specifically, the system  10  may include a vessel  12  having a reel  14  that supplies power/communication cords  16  to a controller  18 . A Mux Reel may be used to transmit power and communication. Some systems have hose reels to transmit fluid under pressure or hard pipe (rigid conduit) to transmit the fluid under pressure or both. Other systems may have a hose with communication or lines (pilot) to supply and operate functions subsea. However, a common feature of these systems is their limited operation depth. The controller  18  is disposed undersea, close to or on the seabed  20 . In this respect, it is noted that the elements shown in  FIG. 1  are not drawn to scale and no dimensions should be inferred from  FIG. 1 . 
       FIG. 1  also shows a wellhead  22  of the subsea well  23  and a drill line  24  that enters the subsea well  23 . At the end of the drill line  24  there is a drill (not shown). Various mechanisms, also not shown, are employed to rotate the drill line  24 , and implicitly the drill, to extend the subsea well. 
     However, during normal drilling operation, unexpected events may occur that could damage the well and/or the equipment used for drilling. One such event is the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure exceeds the pressure of the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent it, the well and/or the associated equipment may be damaged. 
     Thus, a pressure controlling device, for example, a blowout preventer (BOP), might be installed on top of the well to seal the well in case that the integrity of the well is affected. The BOP is conventionally implemented as a valve to prevent the release of pressure either in the annular space between the casing and the drill pipe or in the open hole (i.e., hole with no drill pipe) during drilling or completion operations.  FIG. 1  shows BOPs  26  or  28  that are controlled by the controller  18 , commonly known as a POD. The controller  18  controls an accumulator  30  to close or open BOPs  26  and  28 . More specifically, the controller  18  controls a system of valves (not shown) for opening and closing the BOPs. Hydraulic fluid, which is used to open and close the valves, is commonly pressurized by equipment on the surface. The pressurized fluid is stored in accumulators on the surface and subsea to operate the BOPs. The fluid stored subsea in accumulators may also be used to shear and/or to support acoustic functions when the control of the well is lost. The accumulator  30  may include containers (canisters) that store the hydraulic fluid under pressure and provide the necessary pressure to open and close the BOPs. The pressure from the accumulator  30  is carried by pipe  32  to BOPs  26  and  28 . 
     As understood by those of ordinary skill in the art, in deep-sea drilling, in order to overcome the high hydrostatic pressures generated by the seawater at the depth of operation of the BOPs, the accumulator  30  has to be initially charged to a pressure above the ambient subsea pressure. Typical accumulators are charged with nitrogen but as precharge pressures increase, the efficiency of nitrogen decreases which adds additional cost and weight because more accumulators are required subsea to perform the same operation on the surface. For example, a 60-liter (L) accumulator on the surface may have a useable volume of 24 L on the surface but at 3000 m of water depth the usable volume is less than 4 L. To provide that additional pressure deep undersea is expensive, the equipment for providing the high pressure is bulky, as the size of the canisters that are part of the accumulator  30  is large, and the range of operation of the BOPs is limited by the initial pressure difference between the charge pressure and the hydrostatic pressure at the depth of operation. 
     In this regard,  FIG. 2  shows the accumulator  30  connected via valve  34  to a cylinder  36 . The cylinder  36  may include a piston (not shown) that moves when a first pressure on one side of the piston is higher than a second pressure on the other side of the piston. The first pressure may be the hydrostatic pressure plus the pressure released by the accumulator  30  while the second pressure may be the hydrostatic pressure. Therefore, the use of pressured canisters to store high-pressure fluids to operate a BOP make the operation of the offshore rig expensive and require the manipulation of large parts. 
     As discussed above with regard to  FIG. 2 , the accumulator  30  is bulky because of the low efficiency of nitrogen at high pressures. As the offshore fields are located deeper and deeper (in the sense that the distance from the sea surface to the seabed is becoming larger and larger), the nitrogen based accumulators become less efficient given the fact that the difference between the initial charge pressure to the local hydrostatic pressure decreases for a given initial charge, thus, requiring the size of the accumulators to increase (it is necessary to use 16 320-L bottles or more depending on the required shear pressure and water depth), and increasing the price to deploy and maintain the accumulators. 
     As disclosed in U.S. patent application Ser. No. 12/338,652, filed on Dec. 18, 2008, entitled “Subsea Force Generating Device and Method” to R. Gustafson, the entire disclosure of which is incorporated herein, a novel arrangement, as shown in  FIG. 3 , may be used to generate the force F.  FIG. 3  shows an enclosure  36  that includes a piston  38  capable of moving inside the enclosure  36 . The piston  38  divides the enclosure  36  into a chamber  40 , defined by the cylinder  36  and the piston  38 . Chamber  40  is called the closing chamber. Enclosure  36  also includes an opening chamber  42  as shown in  FIG. 3 . The enclosure  36  may be formed in a BOP and the opening chamber  42  and the closing chamber  40  actuate the ram block (not shown) connected to rod  44 . 
     The pressure in both chambers  40  and  42  may be the same, i.e., the sea pressure (ambient pressure). The ambient pressure in both chambers  40  and  42  may be achieved by allowing the sea water to freely enter these chambers via corresponding valves (not shown). Thus, as there is no pressure difference on either side of the piston  38 , the piston  38  is at rest and no force F is generated. 
     When a force is necessary to be supplied for activating a piece of equipment, the rod  44  associated with the piston  38  has to be moved. This may be achieved by generating a pressure imbalance on two sides of the piston  38 . 
     Although the arrangement shown in  FIG. 3  and described in patent application Ser. No. 12/338,652, to R. Gustafson discloses how to generate the undersea force without the use of the accumulators, however, as discussed later, the accumulators still may be used to supply a supplemental pressure.  FIG. 3  shows that the opening chamber  42  may be connected to a low pressure recipient  60 . A valve  62  may be inserted between the opening chamber  42  and the low pressure recipient  60  to control the pressures between the opening chamber  42  and the low pressure recipient  60 . 
     As shown in  FIG. 3 , when there is no need to supply the force, the pressure in both the closing and opening chambers is P amb  while the pressure inside the recipient  60  is approximately P r =1 atm or lower to improve efficiency. When a force is required for actuation of a piece of equipment of the rig, for example, a ram block of the BOP, the seawater is prevented to enter the opening chamber  42  and valve  62  opens such that the opening chamber  42  may communicate with the low pressure recipient  60 . The following pressure changes take place in the closing chamber  40 , the opening chamber  42  and the low pressure recipient  60 . The closing chamber  40  remains at the ambient pressure as more seawater enters via pipe  64  to the closing chamber  40  as the piston  38  starts moving from left to right in  FIG. 4 . The pressure in the opening chamber  42  decreases as the low pressure P r  becomes available via the valve  62 , i.e., seawater from the opening chamber  42  moves to the low pressure recipient  60  to equalize the pressures between the opening chamber  42  and the low pressure recipient  60 . Thus, a pressure imbalance occurs between the closing chamber  40  and the opening chamber  42  (which is now sealed from the ambient) and this pressure imbalance triggers the movement of the piston  38  to the right in  FIG. 3 , thus generating the force F. 
     One feature of the device shown in  FIG. 3  is the fact that the low pressure recipient  60  has a limited functionality. More specifically, once the seawater from the opening chamber  42  was released into the low pressure recipient  60  and the opening chamber  42  was sealed from ambient, the low pressure recipient  60  cannot again supply the low pressure unless a mechanism is implemented to empty the low pressure recipient  60  of the received sea water. In other words, the seawater that occupies the low pressure recipient  60  after valve  62  has been opened, has to be removed and the gas at the atmospheric pressure that existed in the low pressure recipient  60  prior to opening the valve  62  has to be reestablished for recharging the low pressure recipient  60 . 
     According to an exemplary embodiment and as shown in  FIG. 4 , the low pressure recipient  60  may be reused by providing a reset recipient  70  connected to the low pressure recipient  60 , as described in U.S. patent application Ser. No. 12/338,669, filed on Dec. 18, 2008, entitled “Rechargeable Subsea Force Generating Device and Method” to R. Gustafson, the entire disclosure of which is incorporated herein. The reset recipient  70  and the low pressure recipient  60  may be formed integrally, i.e., in one piece.  FIG. 4  shows the low pressure recipient  60  and the reset recipient  70  formed in a single reset module  72 . 
     The low pressure recipient  60  may include a movable piston  74  that defines a low pressure gas chamber  76 . This low pressure gas (or vacuum) chamber  76  is the chamber that is filled with gas (air for example) at atmospheric pressure and provides the low pressure to the opening chamber  42  of the BOP. The low pressure recipient  60  may include a port  78 , which may be a hydraulic return port to the BOP. 
     A piston assembly  80  penetrates into the low pressure recipient  60 . The piston assembly  80  is provided in the reset recipient  70 . The piston assembly  80  includes a piston  82  and a first extension element  84 . The piston  82  is configured to move inside the reset recipient  70  while the first extension element  84  is configured to enter the low pressure recipient  60  to apply a force to the piston  74 . The piston  82  divides the reset recipient  70  into a reset opening retract chamber  86  and a reset closing extend chamber  88 . The reset opening retract chamber  86  is configured to communicate via a port  90  with a pressure source (not shown). The reset closing extend chamber  88  is configured to communicate via a port  92  to the pressure source or another pressure source. The release of the pressure from the pressure source to the reset recipient  70  may be controlled by valves  94  and  96 . A solid wall  98  may be formed between the low pressure recipient  60  and the reset recipient  70  to separate the two recipients. A second extension element  100  of the piston  82  may be used to lock the piston  82 . The piston  82  may be locked in a desired position by a locking mechanism  102 . Mechanisms for locking a piston are know in the art, for example, Hydril Multiple Position Locking (MPL) clutch, from Hydril Company LP, Houston, Tex. or other locking device such as a collet locking device or a ball grip locking device. 
     However, it would be desirable to provide other systems and methods for recharging the low pressure recipient. 
     SUMMARY 
     According to one exemplary embodiment, there is a recharging mechanism for resetting a pressure in a low pressure recipient connected to a subsea pressure control device. The recharging mechanism includes the low pressure recipient configured to have first and second chambers, the first chamber being configured to receive a hydraulic liquid at a high pressure and the second chamber being configured to include a gas at a low pressure; a valve fluidly connected to a first port of the first chamber of the low pressure recipient; a pumping device fluidly connected to a second port of the first chamber of the low pressure recipient; and a blowout preventer (BOP) section fluidly connected to the valve and configured to close or open a ram block. The pumping device is configured to evacuate the hydraulic fluid from the first chamber of the low pressure recipient when the valve closes a fluid communication between the first port of the first chamber and the BOP section. 
     According to another exemplary embodiment, there is a pumping device configured to reestablish a low pressure in a low pressure recipient connected to a subsea pressure control device. The pumping device includes first and second enclosures connected to each other by a passage; a piston provided in the first enclosure to split the first enclosure in first and second chambers; a first port connected to the first chamber and configured to fluidly communicate with a source of high pressure; a second port connected to the second chamber and configured to fluidly communicate with the source of high pressure; and a rod connected to the piston and configured to extend through the first enclosure, the passage and the second enclosure in such a way that a fluid from the second enclosure is prevented to enter the first enclosure. 
     According to still another exemplary embodiment, there is a method for reestablishing a low pressure in a low pressure recipient with a pumping device. The method includes a step of connecting first and second enclosures of the pumping device to each other by a passage; a step of providing a piston in the first enclosure that splits the first enclosure in first and second chambers; a step of connecting a first port to the first chamber to fluidly communicate with a source of high pressure; a step of connecting a second port to the second chamber to fluidly communicate with the source of high pressure; and a step of connecting a rod to the piston to extend through the first enclosure, the passage and the second enclosure in such a way that a fluid from the second enclosure is prevented to enter the first enclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings: 
         FIG. 1  is a schematic diagram of a conventional offshore rig; 
         FIG. 2  is a schematic diagram of an accumulator for generating an undersea force; 
         FIG. 3  is a schematic diagram of a low pressure recipient connected to a BOP; 
         FIG. 4  is a schematic diagram of a device for recharging a low pressure recipient; 
         FIG. 5  is a schematic diagram of a pumping system for recharging a low pressure recipient according to an exemplary embodiment; 
         FIG. 6  is a more detailed schematic diagram of a pumping system for recharging a low pressure recipient according to an exemplary embodiment; 
         FIG. 7  is a schematic diagram of a device used to control an undersea well; 
         FIG. 8  is a schematic diagram of a pumping system according to an exemplary embodiment; and 
         FIG. 9  is a flow chart of a method for recharging a low pressure recipient according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of BOP systems. However, the embodiments to be discussed next are not limited to these systems, but may be applied to other systems that require the repeated supply of force when the ambient pressure is high such as in a subsea environment, as for example a subsea pressure control device. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
     According to an exemplary embodiment, a novel way to recharge a low pressure recipient is discussed next. According to this embodiment, a pump may be connected to the low pressure recipient to remove the seawater or other fluid and reestablish a low pressure of a gas inside the low pressure recipient. The pump may be configured to vent into the sea the seawater from the low pressure recipient or to recirculate the seawater. The pump may be configured to handle one or more low pressure recipients. The pump may be placed undersea, next to the low pressure recipient or on a ship above the well. 
     According to an exemplary embodiment illustrated in  FIG. 5 , a recharging system  110  may include the low pressure recipient  60 , a pumping device  120 , a BOP section  140 , and a valve  140 . The pumping device  120  may have ports  122  and  124  that activate the pumping device for removing the seawater from the low pressure recipient  60 . A fluid connection  160  (e.g., pipe) is provided between the pumping device  120  and the low pressure recipient  60 . 
     Valve  150  is configured to place in fluid communication the low pressure recipient  60  with an opening chamber  142  the BOP section  140  and also to allow a pressure source  170  to provide pressure to the BOP section  140 , as will be discussed later. Another pressure source may be connected to a closing chamber  144  of the BOP section  140  and this pressure source may include another low pressure recipient  180 , one or more accumulators  182 , and/or a pipe  184  connected to a ship (not shown) at the sea level. All these power sources are connected to a port  186  of the BOP section  140 . Pipe  184  may be connected to a pump provided on the ship. BOP section  140  is part of a BOP and includes the closing and opening mechanism for a ram block  146  that is connected via a rod  148  to a piston  149 . The pressure differences on the piston  149 , pressures created in the closing chamber  144  and the opening chamber  142 , determine the movement direction of the ram block  146 . 
     According to an exemplary embodiment illustrated in  FIG. 6 , the low pressure recipient  60  has a piston  74  that separates gas chamber  76  from chamber  77 . However, according to another exemplary embodiment, the piston  74  may be removed as the gas in the gas chamber  76  separates from a fluid in the chamber  77  due, for example, to gravity. Gas chamber  76  is configured to hermetically seal a gas provided in this chamber. The gas is provided at sea level to have a pressure around 1 atm. One possible gas is air. However, it is possible to provide vacuum in gas chamber  76 . Optional piston  74  is provided with seals (not shown) where contacting the inside wall of the low pressure recipient  60  to prevent an escape of the gas from gas chamber  76  or to prevent sea water (or other fluid) from chamber  77  entering the gas chamber  76 . Thus, in one application, gas chamber  76  is completely isolated from ambient or other mediums, i.e., there are no ports or valves connected to the gas chamber  76 . On the contrary, chamber  77  is connected via a first port  79   a  to the valve  150  and to the BOP section  140  and via a second port  79   b  to pipe  160  and to the pumping device  120 . 
     Pumping device  120  may include a pump or a similar device that is capable of moving a fluid. According to an exemplary embodiment, the pumping device  120  includes a first enclosure  126  and a second enclosure  128  connected to each other via a passage  130 . The first enclosure  126  has a larger cross-sectional area A 1  than a cross-sectional area A 2  of the second enclosure  128 . The cross-sectional areas A 1  and A 2  represent the area of each of the enclosures taken substantially perpendicular on axis X along which a piston  132  moves inside the first enclosure  126 . Piston  132  is connected to a rod  134  that extends in the first enclosure  126 , the passage  130 , and the second enclosure  128 . A cross-sectional area A 3  of the rod  134  may be smaller than area A 2 . Optionally, a piston  136  having area A 3  may be connected to the rod  134 . Areas A 1  to A 3  may be chosen to amplify the effect on the pump. By providing an appropriate pressure at ports  122  and/or  124 , the piston  132  is forced to move along axis X. Thus, rod  134  moves inside the second chamber  128  to absorb fluid from chamber  77  and to discharge the absorbed fluid outside the pumping device  120 . 
     A movement of the rod  134  along a direction opposite to X absorbs the seawater from chamber  77  of the low pressure recipient  60 . A movement of the rod  134  along X forces the seawater absorbed from chamber  77  along pipe  137 . Valves  190  and  192  (directional valves configured to allow a flow only in one direction) prevent the seawater from entering back into chamber  77  or absorbing the seawater along pipe  137 . Pipe  137  may be configured to release the seawater in the ambient or may send the seawater along pipe  194  and  174  to the pressure source  170 . Piston  132  may have a seal  138  for reducing fluid communication between the chambers  126   a  and  126   b  of the first enclosure  126 . 
     Chamber  77  of the low pressure recipient  60  also communicates with valve  150 . Valve  150  may be a conventional sub plate mounted (SPM) valve or other known valve. An SPM valve is actuated between the various positions by a pilot valve  152 . The pilot valve  152  may be a solenoid valve (electrically activated valve). The pilot valve  152  is connected to the SPM valve  150  as shown in the figure. 
     In one application, both the SPM valve  150  and the pilot valve  152  are provided in the MUX POD (not shown) device. The MUX POD may be located on the lower marine riser package (LMRP) while the BOP section  140  is located on the BOP stack. In this regard,  FIG. 7  schematically illustrates the possible distribution of the elements discussed above. In this exemplary embodiment, the well head  200  is connected to the sea floor  202  and also to the BOP stack  204 . The BOP stack  204  is connected to the LMRP  206  which in turn is connected via a riser  208  to a ship  210  at sea level  212 . The MUX POD  214 , which hosts the SPM valve  150  and the pilot valve  152  may be located on the LRMP  206 . In other embodiment, the SPM valve  150  and the pilot valve  152  are located in a kicker pod  216  that is located on the BOP stack  204 . The kicker pod  216  may include two connecting parts, one including the SPM valve  150  and one including the pilot valve  152 . The part including the SPM valve  150  may be fixedly connected to the BOP stack  204  while the part including the pilot valve  152  is removably connected to the other part. Thus, the part including the pilot valve  152  may be removed by a remote operated vehicle (ROV) from the BOP stack  204 . 
     Returning to  FIG. 6 , SPM valve  150  may include various ports  150   a  to  150   d , which are configured to block or allow a fluid flow as indicated by the figure. Port  150   b  communicates with chamber  77  of the low pressure recipient  60  and blocks a fluid communication between chamber  77  and the BOP section  140 . Port  150   c  allow a communication between pressure source  170  and the BOP section  140 . When activated to the other position, port  150   a  of the SPM valve  150  blocks the fluid communication with the pressure source  170  and allows fluid communication between chamber  77  and the BOP section  140 . Thus, in the position not shown in  FIG. 6 , the fluid in the opening chamber  142  is allowed to enter chamber  77  of the low pressure recipient  60  and to close the ram block  146  (see  FIG. 5 ) by moving piston  149  from left to right in the figure. 
     After this operation is performed, the SPM valve  150  moves in the position shown in  FIG. 6  to block fluid communication to chamber  77 . At this stage, as shown in  FIG. 8 , piston  74  (if the low pressure recipient  60  has not piston  74 , the fluid in chamber  77  compresses the gas in chamber  76 ) has compressed the gas in the gas chamber  76  and chamber  77  is full with sea water. This sea water needs now to be removed so that piston  74  may come back to the initial position shown in  FIG. 6 . Pumping device  120  is used to achieve this functionality as already discussed. 
     Pressure source  170  may be used to provide the necessary high pressure for closing the ram block in the BOP section  140 . The pressure source  170  may include, for example, an enclosure  172 . The enclosure  172  may be configured to hold a fluid under pressure. The enclosure  172  may also be configured to directly communicate via a pipe  174  with the ship  210  for receiving more pressure under given conditions. Alternatively, the enclosure  172  may be connected to the pumping device  120 , via pipe  194 , to boost its pressure. 
     According to an exemplary embodiment, at least a pressure sensor may be provided in chamber  76  of the low pressure recipient  60  to monitor the low pressure in this chamber. Further, according to another exemplary embodiment, position detection sensors as described in U.S. Provisional Patent Application Ser. No. 61/138,005, filed on Dec. 16, 2008, to R. Judge, the entire disclosure of which is incorporated herein by reference, may be provided (i) in the pumping device  120  to detect the position of piston  132 , (ii) in the low pressure recipient  60  to detect the position of piston  74 , and/or (iii) in the BOP section  140  to detect the position of piston  149 . Knowing some or all of the positions of the pistons  74 ,  132 , and/or  149 , may allow a controller (not shown) to control the release of high pressure from power source  170  to port  152   c  and also to control valve  152  and the pumping device  120 . 
     According to an exemplary embodiment illustrated in  FIG. 9 , there is a method for reestablishing a low pressure in a low pressure recipient with a pumping device. The method includes a step  900  of connecting first and second enclosures of the pumping device to each other by a passage, a step  902  of providing a piston in the first enclosure that splits the first enclosure in first and second chambers, a step  904  of connecting a first port to the first chamber to fluidly communicate with a source of high pressure, a step  906  of connecting a second port to the second chamber to fluidly communicate with the source of high pressure, and a step  908  of connecting a rod to the piston to extend through the first enclosure, the passage and the second enclosure in such a way that a fluid from the second enclosure is prevented to enter the first enclosure. 
     The disclosed exemplary embodiments provide a device and a method for repeatedly recharging a low pressure recipient. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. 
     Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. 
     This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.