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BACKGROUND  
         [0001]    This invention relates generally to wellbores, and in particular to cementing systems for wellbores.  
           [0002]    Referring to FIG. 1 a , a conventional system  10  for cementing a wellbore  12  includes a shoe  14  defining a passage  14   a  that is coupled to an end of a tubular member  16  defining a passage  16   a . The tubular member  16  typically includes one or more tubular members threadably coupled end to end. The other end of the tubular member  16  is coupled to an end of a float collar  18  including a float  18   a . The other end of the float collar  18  is coupled to an end of a tubular member  20  defining a passage  20   a . Centralizers  22   a ,  22   b , and  22   c  are coupled to the exteriors of the tubular members,  16  and  18 . More generally, the system  10  may include any number of centralizers. The other end of the tubular member  20  is coupled to a fluid injection assembly  24  defining a passage  24   a  and radial passages  24   b ,  24   c , and  24   d , and including retaining pins  24   e  and  24   f . The fluid injection head  24  is commonly referred to as a cementing head. A bottom cementing plug  26  and a top cementing plug  28  are retained within the passage  24   a  of the fluid injection assembly  24  by the retaining pins  24   e  and  24   f . The bottom cementing plug  26  typically includes a longitudinal passage that is sealed off by a frangible diaphragm.  
           [0003]    During operation, as illustrated in FIG. 1 a , drilling mud  30  is circulated through the wellbore  12  by injecting the drilling mud into the fluid injection assembly  24  through the radial passage  24   b . The drilling mud  30  then passes through the passages  24   a ,  20   a ,  18   a , and  14   a  into the annulus between the tubular member  20 , the float collar  18 , the tubular member  16 , and the shoe  14 . As illustrated in FIG. 1 b , the bottom cementing plug  26  is then released and a spacer fluid  32  followed by a cement slurry  34  are injected into the injection assembly  24  through the radial passage  24   c  behind and above the bottom cementing plug. As illustrated in FIG. 1 c , the top cementing plug  28  is then released and a displacing fluid  36  is injected into the injection assembly  24  through the radial passage  24   d  behind and above the top cementing plug. As illustrated in FIG. 1 d , the continued injection of the displacing fluid  36  displaces the bottom cementing plug  26  into contact with the float collar  18  and breaks the frangible membrane of the bottom cementing plug thereby causing the cement slurry  34  to flow into the annulus between the wellbore  12  and the shoe  14 , the tubular member  16 , the float collar  18 , and the tubular member  20 . As illustrated in FIG. 1 e , the continued injection of the displacing fluid  36  then displaces the top cementing plug  28  downwardly until the top cementing plug impacts the bottom cementing plug  26 . The float element  18   a  of the float collar  18  prevents back flow of the cement slurry  34  into the tubular member  20 . The cement slurry  34  may then be allowed to cure.  
           [0004]    Referring to FIG. 2 a , another conventional system  100  for cementing a wellbore  102  having a preexisting wellbore casing  104  includes a float shoe  106  including a float element  106   a  that is coupled to an end of a tubular member  108  defining a passage  108   a . The other end of the tubular member  108  is coupled to an end of a landing collar  110  defining a passage  110   a . The other end of the landing collar  110  is coupled to an end of a tubular member  112  defining a passage  112   a . A liner hanger  114  is coupled to the tubular member  112  for permitting the tubular member to be coupled to and supported by the preexisting wellbore casing  104 . A centralizer  116  is also coupled to the exterior of the tubular member  112  for centrally positioning the tubular member inside the preexisting wellbore casing  104 . An end of a tubular support member  118  defining a passage  118   a  extends into the other end of the tubular member  112 . A releasable coupling  120  is coupled to the tubular support member  118  for releasably coupling the tubular support member to the tubular member  112 . A wiper plug  122  defining a restricted passage  122   a  is coupled to an end of the tubular support member  118  within the other end of the tubular member  112 . A bumper  124  and a cup seal  126  are coupled to the exterior of the end of the tubular support member  118  within the tubular member  112 .  
           [0005]    During operation, as illustrated in FIG. 2 a , drilling mud  128  is circulated through the wellbore  102  by injecting the drilling mud through the passages  118   a ,  122   a ,  112   a ,  110   a ,  108   a , and  106   a  into the annulus between the float shoe  106 , the tubular member  108 , the landing collar  110 , and the tubular member  112 . As illustrated in FIG. 2 b , a spacer fluid  130  followed by a cement slurry  132  are then injected into the passages  118   a ,  122   a , and  112   a  behind and above the drilling mud  128 . As illustrated in FIG. 2 c , a pump down plug  134  is then injected into the passage  118   a  followed by a displacing fluid  136 . As illustrated in FIG. 2 d , the continued injection of the displacing fluid  136 , causes the pump down plug  134  to engage the restricted passage  122   a  of the wiper plug  122  thereby disengaging the wiper plug from the end of the tubular support member  118 . As a result, the wiper plug  122  and the pump down plug  134  are driven downwardly within the tubular member  112  by the continued injection of the displacing fluid  136  which in turn displaces the spacer fluid  130  and the cement slurry  132  into the annulus between the wellbore  102  and the float shoe  106 , the tubular member  108 , the landing collar  110  and the tubular member. As illustrated in FIG. 2 e , the continued injection of the displacing fluid  136  causes the wiper plug  122  and the pump down plug  134  to impact the landing collar  110  and engage the passage  110   a . Furthermore, as illustrated in FIG. 2 e , the continued injection of the displacing fluid  136  fills the annulus between the wellbore  102  and the tubular member  112  with the cement slurry  132 . The float element  106   a  of the float shoe  106  prevents back flow of the cement slurry into the tubular member  108 . As illustrated in FIG. 2 f , the tubular support member  118  is then decoupled from the tubular member  112  and raised away from the end of the tubular member  112 . The spacer liquid  130  and any excess cement slurry  132  may then be removed by circulating drilling mud  138  through the annulus between the tubular support member  118  and the preexisting wellbore casing  104 . The cement slurry  132  may then be allowed to cure.  
           [0006]    Referring to FIG. 3 a , yet another conventional system  200  for cementing a wellbore  202  having a preexisting wellbore casing  204  includes a float shoe  206  including a float element  206   a  that is coupled to an end of a tubular member  208  defining a passage  208   a . The other end of the tubular member  208  is coupled to an end of a landing collar  210  defining a passage  210   a . The other end of the landing collar  210  is coupled to an end of a tubular member  212  defining a passage  212   a . A centralizer  214  is coupled to the exterior of the tubular member  212  for centrally positioning the tubular member inside the preexisting wellbore casing  204 . An end of a tubular support member  216  defining a passage  216   a  extends into the other end of the tubular member  212  and the other end of the tubular support member  216  is coupled to a conventional subsea cementing head. A releasable coupling  218  is coupled to the tubular support member  216  for releasably coupling the tubular support member to the tubular member  212 . A wiper plug  220  defining a restricted passage  220   a  is coupled to an end of the tubular support member  216  within the other end of the tubular member  212 . A bumper  222  and a cup seal  224  are coupled to the exterior of the end of the tubular support member  216  within the tubular member  212 .  
           [0007]    During operation, as illustrated in FIG. 3 a , drilling mud  226  is circulated through the wellbore  202  by injecting the drilling mud through the passages  216   a ,  220   a ,  212   a ,  210   a ,  208   a , and  206   a  into the annulus between the float shoe  206 , the tubular member  208 , the landing collar  210 , and the tubular member  212 . As illustrated in FIG. 3 b , a spacer fluid  228  followed by a cement slurry  230  are then injected into the passages  216   a ,  220   a , and  212   a  behind and above the drilling mud  226 . As illustrated in FIG. 3 c , a pump down plug  232  is then injected into the passage  216   a  followed by a displacing fluid  234 . As illustrated in FIG. 3 d , the continued injection of the displacing fluid  234 , causes the pump down plug  232  to engage the restricted passage  220   a  of the wiper plug  220  thereby disengaging the wiper plug from the end of the tubular support member  216 . As a result, the wiper plug  220  and the pump down plug  232  are driven downwardly within the tubular member  212  by the continued injection of the displacing fluid  234  which in turn displaces the spacer fluid  228  and the cement slurry  230  into the annulus between the wellbore  202  and the float shoe  206 , the tubular member  208 , the landing collar  210  and the tubular member. As illustrated in FIG. 3 e , the continued injection of the displacing fluid  234  causes the wiper plug  220  and the pump down plug  232  to impact the landing collar  210  and engage the passage  210   a . Furthermore, as illustrated in FIG. 3 e , the continued injection of the displacing fluid  234  fills the annulus between the wellbore  202  and the tubular member  212  with the cement slurry  230 . The float element  206   a  of the float shoe prevents back flow of the cement slurry  230  into the tubular member  208 . The tubular support member  216  is then decoupled from the tubular member  212  and raised out of the wellbore  202 . The cement slurry  230  may then be allowed to cure.  
           [0008]    Thus, conventional systems for cementing a wellbore require the use of a float collar and/or a float shoe in order to prevent the back flow of the cement slurry. As a result, conventional systems for cementing a wellbore typically restrict circulation, and generate surge pressures that can damage the subterranean formations or induce the loss of valuable drilling fluids. Furthermore, conventional systems also increase casing and liner running times and open hole exposure times, and expose floating valves to drilling fluid circulation thereby eroding the floating valves and compromising their proper operation. Furthermore, the conventional equipment used for cementing wellbores are also limited in size, is complex, and is expensive to operate. In addition, because conventional float collars and/or float shoes, and the required related operating equipment, are large, heavy, and fragile, the cost of transporting such equipment is often expensive.  
           [0009]    The present invention is directed to overcoming one or more of the limitations of existing cementing systems for wellbores.  
         SUMMARY  
         [0010]    According to one embodiment of the invention, an apparatus for cementing an annulus between a wellbore casing and a wellbore is provided that includes a landing collar defining a restricted passage, a wellbore casing defining a passage coupled to the landing collar, a top cementing plug for sealingly engaging the wellbore casing, a bottom cementing plug for sealingly engaging the wellbore casing, and a fluid injection assembly coupled to the wellbore casing for injecting fluidic materials into the wellbore casing and controllably releasing the top cementing plug and the bottom cementing plug into the wellbore casing. The bottom cementing plug includes a plug body defining a plug passage, a frangible membrane for sealing the plug passage, and a one-way valve for controlling the flow of fluidic materials through the plug passage.  
           [0011]    According to another embodiment of the invention, a method of cementing an annulus between a wellbore casing and a wellbore is provided that includes positioning a wellbore casing defining a passage and including a landing collar at one end defining a restricted passage into the wellbore, injecting a non-hardenable fluidic material into the other end of the wellbore casing, injecting a bottom cementing plug into the other end of the wellbore casing, the bottom cementing plug including a plug body defining a plug passage, a frangible membrane for sealing the plug passage, and a one-way valve for controlling the flow of fluidic materials through the plug passage, injecting a hardenable fluidic sealing material into the other end of the wellbore casing, injecting a top cementing plug into the other end of the wellbore casing, injecting a non-hardenable fluidic material into the other end of the wellbore casing, breaking the frangible membrane of the bottom cementing plug to permit the hardenable fluidic sealing material to pass through the plug passage, the one-way valve, and the restricted passage into the annulus between the tubular member and the wellbore, and the one-way valve preventing the hardenable fluidic sealing material from passing from annulus back into the wellbore casing.  
           [0012]    According to another embodiment of the invention, a system for cementing an annulus between a wellbore casing and a wellbore is provided that includes means for positioning the wellbore casing into the wellbore, means for injecting a non-hardenable fluidic material into the wellbore casing, means for injecting a hardenable fluidic sealing material into the wellbore casing, means for separating the non-hardenable fluidic material and the hardenable fluidic sealing material within the wellbore casing, means for pressurizing the hardenable fluidic sealing material within the wellbore casing, means for controllably releasing the hardenable fluidic sealing material into the annulus between the wellbore casing and the wellbore, and means for preventing the hardenable fluidic sealing material from flowing from the annulus into the wellbore casing.  
           [0013]    According to another embodiment of the invention, a bottom cementing plug for use in a system for cementing an annulus between a wellbore casing and a wellbore is provided that includes a plug body defining a plug passage, a sealing element coupled to the plug body for sealingly engaging the wellbore casing, a frangible membrane for sealing the plug passage, and a one-way valve for controlling the flow of fluidic materials through the plug passage.  
           [0014]    According to another embodiment of the invention, an apparatus for cementing an annulus between a tubular liner and a wellbore including a preexisting wellbore casing is provided that includes a tubular support member, a wiper plug releasably coupled to an end of the tubular support member, a tubular liner releasably coupled to tubular support member, a landing collar defining a restricted passage coupled to an end of the tubular liner, a cementing plug for sealingly engaging the tubular liner and releasably coupled to the wiper plug, including a plug body defining a plug passage and a valve for controlling the flow of fluidic materials through the plug passage, and a fluid injection assembly coupled to the tubular support member for injecting fluidic materials into the tubular support member and controllably releasing a ball and a pump down plug into the tubular support member for engaging the cementing plug and the wiper plug.  
           [0015]    According to another embodiment of the invention, a method of cementing an annulus between a tubular liner and a wellbore including a preexisting wellbore casing is provided that includes releasably supporting a tubular liner defining a passage and including a landing collar at one end defining a restricted passage within the wellbore using a tubular support member defining a passage fluidicly coupled to the passage of the tubular liner and including a wiper plug releasably coupled to an end of the tubular support member, releasably coupling a cementing plug to the wiper plug within the tubular member, the cementing plug including a plug body defining a plug passage and a valve for controlling the flow of fluidic materials through the plug passage, injecting a non-hardenable fluidic material into the passage of the tubular support member, injecting a ball into the passage of the tubular support member, injecting a hardenable fluidic sealing material into the passage of the tubular support member, the ball decoupling the cementing plug from the wiper plug, the cementing plug engaging the landing collar, injecting a pump down plug into the passage of the tubular support member, injecting a non-hardenable fluidic material into the passage of the tubular support member, decoupling the wiper plug from the end of the tubular support member, and the wiper plug and the pump down plug engaging the cementing plug.  
           [0016]    According to another embodiment of the invention, a system for cementing an annulus between a tubular liner and a wellbore is provided that includes means for injecting a non-hardenable fluidic material into the tubular liner, means for injecting a hardenable fluidic sealing material into the tubular liner, means for separating the non-hardenable fluidic material and the hardenable fluidic sealing material within the tubular liner, means for pressurizing the hardenable fluidic sealing material within the tubular liner, means for controllably releasing the hardenable fluidic sealing material into the annulus between the tubular liner and the wellbore, and means for preventing the hardenable fluidic sealing material from flowing from the annulus into the tubular liner.  
           [0017]    According to another embodiment of the invention, a bottom cementing plug for use in a system for cementing an annulus between a wellbore casing and a wellbore is provided that includes a plug body defining a passage, a frangible ball seat positioned within one end of the passage, a one way valve positioned within another end of the passage for controlling the flow of fluidic materials through the passage, and a frangible retaining member positioned within the other end of the passage for retaining the one way valve in a stationary position.  
           [0018]    The present embodiments of the invention provide a number of advantages over conventional systems for cementing wellbores. For example, the present embodiments of the invention eliminate the float collar that is required in conventional systems. As a result, during the operation of the present embodiments of the invention, drilling mud does not have to be circulated in order to stabilize the wellbore prior to cementing. Furthermore, the present embodiments of the invention also permit a larger internal diameter system to be used throughout thereby increasing the operational efficiency. In addition, the surge pressures created by conventional float collars is eliminated by the present embodiments of the invention. Furthermore, the operational and logistical costs associated with shipping and assembling the float collar, and related equipment, are eliminated by the present embodiments of the invention. In addition, the present embodiments of the invention reduce restrictions to circulation, reduce surge pressures, reduce fluid losses to the subterranean formation, reduce casing and liner running times, reduces the open hole time, and reduces the loss of valuable drilling fluids to the formation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIGS. 1 a - 1   e  are fragmentary cross-sectional illustrations of an embodiment of a conventional system for cementing a wellbore.  
         [0020]    [0020]FIGS. 2 a - 2   f  are fragmentary cross-sectional illustrations of another embodiment of a conventional system for cementing a wellbore.  
         [0021]    [0021]FIGS. 3 a - 3   e  are fragmentary cross-sectional illustrations of another embodiment of a conventional system for cementing a wellbore.  
         [0022]    [0022]FIGS. 4 a - 4   e  are fragmentary cross-sectional illustrations of an embodiment of a system for cementing a wellbore.  
         [0023]    [0023]FIG. 5 is a cross-sectional illustration of an embodiment of a bottom cementing plug for use in the system of FIGS. 4 a - 4   e.    
         [0024]    [0024]FIG. 6 is a cross-sectional illustrations of an embodiment of a bottom cementing plug for use in the system of FIGS. 4 a - 4   e.    
         [0025]    [0025]FIG. 7 is a cross-sectional illustrations of an embodiment of a bottom cementing plug for use in the system of FIGS. 4 a - 4   e.    
         [0026]    [0026]FIGS. 8 a - 8   f  are fragmentary cross-sectional illustrations of an embodiment of a system for cementing a wellbore.  
         [0027]    [0027]FIG. 9 a  is a cross-sectional illustration of an embodiment of a bottom cementing plug for use in the system of FIGS. 8 a - 8   f  in an initial operational position.  
         [0028]    [0028]FIG. 9 b  is an illustration of bottom cementing plug of FIG. 9 a  after removing the ball seat and flapper valve retainer.  
         [0029]    [0029]FIG. 9 c  is an illustration of bottom cementing plug of FIG. 9 b  after rotating the flapper valve to the closed position.  
         [0030]    [0030]FIG. 9 d  is an illustration of an alternative embodiment of the bottom cementing plug of FIG. 9 a.    
         [0031]    [0031]FIG. 9 e  is a top view of the bottom cementing plug of FIG. 9 d.    
         [0032]    [0032]FIG. 9 f  is a cross sectional illustration of the bottom cementing plug of FIG. 9 d.    
         [0033]    [0033]FIGS. 10 a - 10   e  are fragmentary cross-sectional illustrations of an embodiment of a system for cementing a wellbore.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]    Referring to FIGS. 4 a - 4   e , the reference numeral  400  refers, in general, to a system for cementing a wellbore  402  according to an embodiment of the invention that includes a shoe  404  defining a passage  404   a  that is coupled to an end of a tubular member  406  defining a passage  406   a . The other end of the tubular member  406  is coupled to an end of a landing collar  408  defining a passage  408   a . The other end of the landing collar  408  is coupled to an end of a tubular member  410  defining a passage  410   a . Centralizers  412   a ,  412   b , and  412   c  may be coupled to the exteriors of the tubular members,  406  and  410 . The other end of the tubular member  410  is coupled to a fluid injection assembly  414  defining a passage  414   a  and radial passages  414   b ,  414   c , and  414   d , and including retaining pins  414   e  and  414   f . A bottom cementing plug  416  and a top cementing plug  418  are retained within the passage  414   a  of the fluid injection assembly  414  by the retaining pins  414   e  and  414   f.    
         [0035]    Referring to FIG. 5, in an exemplary embodiment, the bottom cementing plug  416  includes a tubular body  416   a  defining a passage  416   aa  and a passage  416   ab . A frangible disc  416   b  is coupled to an end of the tubular body  416   a  to seal off an end of the passage  416   aa . A flapper check valve  416   c  is pivotally coupled to the other end of the tubular body  416   a  by a pivot support  416   d  and positioned within the intersection of the passages,  416   aa  and  416   ab , for preventing the flow of fluidic materials from the passage  416   ab  into the passage  416   aa . In an exemplary embodiment, the flapper check valve  416   c  is resiliently biased to pivot about the pivot support  416   d  and thereby close off the passage  416   aa . A resilient tubular sealing member  416   e  is coupled to the exterior of the tubular body  416   a  for sealing the interface between the bottom cementing plug  416  and the tubular member  410 . During operation, the flapper check valve  416   c  permits fluidic materials to flow from the passage  416   aa  into the passage  416   ab , and prevents fluidic materials from flowing from the passage  416   ab  into the passage  416   aa.    
         [0036]    During operation, as illustrated in FIG. 4 a , drilling mud  420  is circulated through the wellbore  402  by injecting the drilling mud into the fluid injection assembly  414  through the radial passage  414   b . The drilling mud  420  then passes through the passages  414   a ,  410   a ,  408   a ,  406   a , and  404   a  into the annulus between the tubular member  410 , the landing collar  408 , the tubular member  406 , and the shoe  404 .  
         [0037]    As illustrated in FIG. 4 b , the bottom cementing plug  416  is then released and a spacer fluid  422  followed by a cement slurry  424  are injected into the injection assembly  414  through the radial passage  414   c  behind and above the bottom cementing plug.  
         [0038]    As illustrated in FIG. 4 c , the top cementing plug  418  is then released and a displacing fluid  426  is injected into the injection assembly  414  through the radial passage  414   d  behind and above the top cementing plug.  
         [0039]    As illustrated in FIG. 4 d , the continued injection of the displacing fluid  426  further displaces the bottom cementing plug  416  until it impacts and engages the landing collar  408 . Further injection of the displacing fluid  426  pressurizes the portion of the passage  410   a  between the top cementing plug  418  and the bottom cementing plug  416  thereby breaking the frangible disc  416   b . As a result, the cement slurry  424  flows through the passages  416   aa  and  416   ab  of the bottom cementing plug and the passage  408   a  into the annulus between the wellbore  402  and the shoe  404 , the tubular member  406 , the landing collar  408 , and the tubular member  410 .  
         [0040]    As illustrated in FIG. 4 e , the continued injection of the displacing fluid  426  then displaces the top cementing plug  418  downwardly until the top cementing plug impacts the bottom cementing plug  416 . The flapper check valve  416   c  of the bottom cementing plug  416  prevents back flow of the cement slurry  424  into the tubular member  410 . The cement slurry  424  may then be allowed to cure.  
         [0041]    The system  400  provides a number of advantages over conventional systems for cementing wellbores. For example, the system  400  eliminates the float collar that is required in conventional systems. As a result, during the operation of the system  400 , drilling mud does not have to be circulated in order to stabilize the wellbore prior to cementing. Furthermore, the system  400  permits a larger internal diameter to be used throughout thereby increasing the operational efficiency. In addition, the surge pressure created by conventional float collars is eliminated by the system  400 . Furthermore, the operational and logistical costs associated with shipping and assembling the float collar, and related equipment, is eliminated by the system  400 . In addition, the system  400  reduces restrictions to circulation, reduce surge pressures, reduce fluid losses to the subterranean formation, reduce casing and liner running times, reduces the open hole time, and reduces the loss of valuable drilling fluids to the formation.  
         [0042]    In an alternative embodiment, the shoe  404  and the tubular member  406  may be omitted.  
         [0043]    Referring to FIG. 6, an alternative embodiment of a bottom cementing plug  500  includes a tubular body  500   a  defining a passage  500   aa , a passage  500   ab , and a passage  500   ac . A frangible disc  500   b  is coupled to an end of the tubular body  500   a  to seal off an end of the passage  500   aa . A ball valve retaining member  500   c  is coupled to the other end of the tubular body  500   a  within the passage  500   ac . A ball valve  500   d  is positioned within the passage  500   ab  for preventing the flow of fluidic materials from the passage  500   ab  into the passage  500   aa . A resilient tubular sealing member  500   e  is coupled to the exterior of the tubular body  500   a  for sealing the interface between the bottom cementing plug  500  and a tubular member. During operation, the ball valve  500   d  permits fluidic materials to pass from the passage  500   aa  into the passage  500   ac  but prevents the flow of fluidic materials from the passage  500   ac  into the passage  500   aa.    
         [0044]    Referring to FIG. 7, an alternative embodiment of a bottom cementing plug  505  includes a tubular body  505   a  defining a passage  505   aa , a throat passage  505   ab , and a passage  505   ac . A frangible disc  505   b  is coupled to an end of the tubular body  505   a  to seal off an end of the passage  505   aa . A tubular check valve retaining member  505   c  is coupled to the other end of the tubular body  505   a  within the passage  505   ac . A spring  505   d  and a dart check valve  505   e  are positioned within the passage  505   ac  for preventing the flow of fluidic materials from the passage  500   ac  into the passage  505   aa . A resilient tubular sealing member  505   f  is coupled to the exterior of the tubular body  505   a  for sealing the interface between the bottom cementing plug  505  and a tubular member. During operation, the dart check valve  505   e  permits fluidic materials to pass from the passage  505   aa  into the passage  505   ac  but prevents the flow of fluidic materials from the passage  505   ac  into the passage  505   aa.    
         [0045]    In several alternative embodiments, the system  400  utilizes the bottom cementing plugs  500  or  505  in place of the bottom cement plug  416  in order to prevent the back flow of the cement slurry  424  into the tubular member  410 .  
         [0046]    Referring to FIGS. 8 a - 8   f , an alternative embodiment of a system  600  for cementing a wellbore  602  having a preexisting wellbore casing  604  includes a shoe  606  defining a passage  606   a  that is coupled to an end of a tubular member  608  defining a passage  608   a . The other end of the tubular member  608  is coupled to an end of a landing collar  610  defining a passage  610   a . The other end of the landing collar  610  is coupled to an end of a tubular member  612  defining a passage  612   a . A liner hanger  613  is coupled to the exterior of the tubular member  612  for coupling the tubular member  612  to the preexisting wellbore casing  604 . A centralizer  614  may be coupled to the exterior of the tubular member  612  for centrally positioning the tubular member inside the preexisting wellbore casing  604 . An end of a tubular support member  616  defining a passage  616   a  extends into the other end of the tubular member  612 . A releasable coupling  618  is coupled to the tubular support member  616  for releasably coupling the tubular support member to the tubular member  612 . A wiper plug  620  defining a restricted passage  620   a  is releasably coupled to an end of the tubular support member  616  within the other end of the tubular member  612 , and a bottom cementing plug  622  is releasably coupled to and end of the wiper plug  620  within the tubular member. A bumper  624  and a cup seal  626  are coupled to the exterior of the end of the tubular support member  616  within the tubular member  612 .  
         [0047]    As illustrated in FIG. 9 a , in an exemplary embodiment, the bottom cementing plug  622  includes a tubular body  622   a  defining a passage  622   aa  and a passage  622   ab . A frangible tubular ball seat  622   b  is positioned within, and coupled to, the interior surface of an end of the passage  622   aa  aa for receiving a conventional ball. A flapper check valve  622   c  is positioned within, and pivotally coupled to, the interior surface of the passage  622   ab  by a pivot support  622   d  for controllably for preventing the flow of fluidic materials from the passage  622   ab  into the passage  622   aa . In an exemplary embodiment, the flapper check valve  622   c  is resiliently biased to pivot about the pivot support  622   d  and thereby close off the passage  622   aa . An end of a frangible tubular retaining member  622   e  is positioned within, and coupled to, the passage  622   aa . The other end of the frangible tubular retaining member  622   e  extends into the passage  622   ab  for preventing the flapper check valve  622   c  from pivoting to seal off the passage  622   aa . A resilient tubular sealing member  622   f  is coupled to the exterior of the tubular body  622   a  for sealing the interface between the bottom cementing plug  622  and the tubular member  612 . During operation, after the frangible tubular retaining member  622   e  has been removed, the flapper check valve  622   c  permits fluidic materials to flow from the passage  622   aa  into the passage  622   ab , and prevents fluidic materials from flowing from the passage  622   ab  into the passage  622   aa.    
         [0048]    During operation, as illustrated in FIG. 8 a , drilling mud  628  is circulated through the wellbore  602  by injecting the drilling mud through the passages  616   a ,  620   a ,  612   a , the bottom cementing plug  626 , the passages  610   a ,  608   a , and  606   a  into the annulus between the shoe  606 , the tubular member  608 , the landing collar  610 , and the tubular member  612 . A ball  630  is introduced into the injected drilling mud  628  for reasons to be described.  
         [0049]    As illustrated in FIG. 8 b , a spacer fluid  632  followed by a cement slurry  632  are then injected into the passages  616   a ,  620   a , and  612   a  behind and above the drilling mud  628 . The ball  630  impacts and mates with the ball seat  622   b  of the bottom cementing plug  622  and decouples the bottom cementing plug from engagement with the wiper plug  620 . As a result, the bottom cementing plug  622  is displaced downwardly in the tubular member  612  and impacts and engages the landing collar  610 .  
         [0050]    As illustrated in FIG. 8 c , a pump down plug  636  is then injected into the passage  616   a  followed by a displacing fluid  638 . The continued injection of the displacing fluid  638  pressurizes the portion of the passage  612   a  above the bottom cementing plug  622  and ball  630 . As a result, the ball  630  breaks through and removes the frangible ball seat  622   b  and the retaining member  622   e  of the bottom cementing plug  622  and into the passage  608   a  thereby permitting fluidic materials to pass from the passage  612   a , through the passages  622   aa  and  622   ab  of the bottom cementing plug  622 , and into the passage  608   a . As a result, as illustrated in FIG. 9 b , the flapper valve  622   c  is no longer prevented from pivoting to close off the passage  622   a.    
         [0051]    As illustrated in FIG. 8 d , the continued injection of the displacing fluid  638 , causes the pump down plug  636  to engage the restricted passage  620   a  of the wiper plug  620  thereby disengaging the wiper plug from the end of the tubular support member  616 . As a result, the wiper plug  620  and the pump down plug  636  are driven downwardly within the tubular member  612  by the continued injection of the displacing fluid  638  which in turn displaces the spacer fluid  632  and the cement slurry  634  through the passages,  622   aa  and  622   ab , of the bottom cementing plug  626 , through the passages,  610   a ,  608   a , and  606   a , into the annulus between the wellbore  602  and the shoe  606 , the tubular member  608 , the landing collar  610  and the tubular member.  
         [0052]    As illustrated in FIG. 8 e , the continued injection of the displacing fluid  638  causes the wiper plug  620  and the pump down plug  634  to impact and engage the bottom cementing plug  622  and fills the annulus between the wellbore  602  and the tubular member  612  with the cement slurry  632 . The back pressure created by the injected cement slurry  634  then causes the flapper valve  622   c  to pivot and thereby close off the passage  622   aa  as illustrated in FIGS. 8 e  and  9   c . As a result, the back flow of the cement slurry  634  from the passage  608   a  into the passage  612   a  is prevented.  
         [0053]    As illustrated in FIG. 8 f , the tubular support member  616  is then decoupled from the tubular member  612  and raised out of the tubular member  612 . The spacer fluid  632  and cement slurry  634  above the tubular member  612  may then be removed by circulating drilling mud  640  through the annulus between the tubular support member  616  and the preexisting wellbore casing  604 . The cement slurry  634  may then be allowed to cure.  
         [0054]    The system  600  provides a number of advantages over conventional systems for cementing wellbores. For example, the system  600  eliminates the float shoe that is required in conventional systems. As a result, during the operation of the system  600 , drilling mud does not have to be circulated in order to stabilize the wellbore prior to cementing. Furthermore, the system  600  permits a larger internal diameter to be used throughout thereby increasing the operational efficiency. In addition, the surge pressures created by conventional float collars is eliminated by the system  600 . Furthermore, the operational and logistical costs associated with shipping and assembling the float collar, and related equipment, is eliminated by the system  600 . In addition, the system  600  reduces restrictions to circulation, reduce surge pressures, reduce fluid losses to the subterranean formation, reduce casing and liner running times, reduces the open hole time, and reduces the loss of valuable drilling fluids to the formation.  
         [0055]    In an alternative embodiment, the shoe  606  and the tubular member  608  may be omitted from the system  600 .  
         [0056]    In an alternative embodiment of the bottom cementing plug  622 , as illustrated in FIGS. 9 d ,  9   e , and  9   f , the frangible tubular ball seat  622   b  includes a frangible upper tubular ball seat  622   ba  and a lower frangible tubular member  622   bb  that are positioned within, and releasably coupled to, the end of the passage  622   aa . The frangible upper tubular ball seat  622   ba  is fabricated from a resilient and frangible material and defines a central passage  622   baa  and a plurality of auxiliary passages,  622   bab ,  622   bac ,  622   bad , and  622   bae . The frangible lower tubular member  622   bb  is fabricated from a frangible material and defines a central passage  622   bba  and a plurality of auxiliary passages,  622   bbb ,  622   bbc ,  622   bbd , and  622   bbe . In an exemplary embodiment, the auxiliary passages  622   bab ,  622   bac ,  622   bad , and  622   bae  are interleaved with the auxiliary passages  622   bbb ,  622   bbc ,  622   bbd , and  622   bbe . Furthermore, in an initial position, at least a portion of the frangible upper tubular ball seat  622   ba  is spaced apart from the frangible lower tubular member  622   bb . In this manner, in the initial position, fluidic materials may pass through the passages  622   baa  and  622   bba  and a serpentine path defined by the auxiliary passages  622   bab ,  622   bac ,  622   bad , and  622   bae  and the auxiliary passages  622   bbb ,  622   bbc ,  622   bbd , and  622   bbe . In this manner, in the initial position, the volumetric rate of flow of the fluidic materials through the bottom cementing plug  622  is enhanced.  
         [0057]    In a compressed position, such as, for example, when the ball  630  impacts and mates with the frangible tubular ball seat  622   ba , the tubular ball seat  622   ba  is compressed into contact with the frangible lower tubular member  622   bb . As a result, the passages  622   baa  and  622   bba  are sealed off by the ball  630 , and the serpentine path defined by the auxiliary passages  622   bab ,  622   bac ,  622   bad , and  622   bae  and the auxiliary passages  622   bbb ,  622   bbc ,  622   bbd , and  622   bbe  is closed off.  
         [0058]    Referring to FIGS. 10 a - 10   e , an alternative embodiment of a system  700  for cementing a wellbore  702  having a preexisting wellbore casing  704  includes a shoe  706  defining a passage  706   a  that is coupled to an end of a tubular member  708  defining a passage  708   a . The other end of the tubular member  708  is coupled to an end of a landing collar  710  defining a passage  710   a . The other end of the landing collar  710  is coupled to an end of a tubular member  712  defining a passage  712   a . A centralizer  714  may be coupled to the exterior of the tubular member  712  for centrally positioning the tubular member inside the preexisting wellbore casing  704 . An end of a tubular support member  716  defining a passage  716   a  extends into the other end of the tubular member  712 . A releasable coupling  718  is coupled to the tubular support member  716  for releasably coupling the tubular support member to the tubular member  712 . A wiper plug  720  defining a restricted passage  720   a  is coupled to an end of the tubular support member  716  within the other end of the tubular member  712 . The bottom cementing plug  622  is releasably coupled to an end of the wiper plug  720  and positioned within the passage  712   a . A bumper  724  and a cup seal  726  are coupled to the exterior of the end of the tubular support member  716  within the tubular member  712 .  
         [0059]    During operation, as illustrated in FIG. 10 a , drilling mud  728  is circulated through the wellbore  702  by injecting the drilling mud through the passages  716   a ,  720   a ,  712   a , the bottom cementing plug  726 , the passages  710   a ,  708   a , and  706   a  into the annulus between the shoe  706 , the tubular member  708 , the landing collar  710 , and the tubular member  712 . A ball  730  is also injected into the passage  716   a  with the injected drilling mud  728  for reasons to be described.  
         [0060]    As illustrated in FIG. 10 b , a spacer fluid  732  followed by a cement slurry  734  are then injected into the passages  716   a ,  720   a , and  712   a  behind and above the drilling mud  728 . The ball  730  impacts and mates with the ball seat  722   b  of the bottom cementing plug  622  and decouples the bottom cementing plug from engagement with the wiper plug  720 . As a result, the bottom cementing plug  622  is displaced downwardly in the tubular member  712  and impacts the landing collar  710 .  
         [0061]    As illustrated in FIG. 10 c , a pump down plug  736  is then injected into the passage  716   a  followed by a displacing fluid  738 . The continued injection of the displacing fluid  738  pressurizes the portion of the passage  712   a  above the bottom cementing plug  622  and the ball  730 . As a result, the ball  730  breaks through and removes the frangible tubular ball seat  622   b  and tubular retaining member  622   e  of the bottom cementing plug  622  thereby permitting fluidic materials to pass through the passage  622   aa  and  622   ab  of the bottom cementing plug.  
         [0062]    As illustrated in FIG. 10 d , the continued injection of the displacing fluid  738 , causes the pump down plug  736  to engage the restricted passage  720   a  of the wiper plug  720  thereby disengaging the wiper plug from the end of the tubular support member  716 . As a result, the wiper plug  720  and the pump down plug  736  are driven downwardly within the tubular member  712  by the continued injection of the displacing fluid  738  which in turn displaces the spacer fluid  732  and the cement slurry  734  through the bottom cementing plug  622  and the passages,  710   a ,  708   a , and  706   a , into the annulus between the wellbore  702  and the shoe  706 , the tubular member  708 , the landing collar  710  and the tubular member.  
         [0063]    As illustrated in FIG. 10 e , the continued injection of the displacing fluid  736  causes the wiper plug  720  and the pump down plug  734  to impact and engage the bottom cementing plug  622  and fills the annulus between the wellbore  702  and the tubular member  712  with the cement slurry  734 . The back pressure created by the cement slurry  734  pivots the flapper valve  622   c  of the bottom cementing plug  622  to close off the passage  622   aa  thereby preventing back flow of the cement slurry from the passage  708   a  into the passage  712   a.    
         [0064]    The tubular support member  716  may then be decoupled from the tubular member  712  and raised out of the tubular member  712 . The spacer fluid  730  and cement slurry  732  above the tubular member  712  may then be removed by circulating drilling mud through the annulus between the tubular support member  716  and the preexisting wellbore casing  704 . The cement slurry  732  may then be allowed to cure.  
         [0065]    The system  700  provides a number of advantages over conventional systems for cementing wellbores. For example, the system  700  eliminates the float shoe that is required in conventional systems. As a result, during the operation of the system  700 , drilling mud does not have to be circulated in order to stabilize the wellbore prior to cementing. Furthermore, the system  700  permits a larger internal diameter to be used throughout thereby increasing the operational efficiency. In addition, the surge pressures created by conventional float collars is eliminated by the system  700 . Furthermore, the operational and logistical costs associated with shipping and assembling the float collar, and related equipment, is eliminated by the system  700 . In addition, the system  700  reduces restrictions to circulation, reduce surge pressures, reduce fluid losses to the subterranean formation, reduce casing and liner running times, reduces the open hole time, and reduces the loss of valuable drilling fluids to the formation.  
         [0066]    In an alternative embodiment, the shoe  706  and the tubular member  708  may be omitted from the system  700 .  
         [0067]    It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, the present systems for cementing a wellbore can be utilized to provide an annular layer of cement around a pipeline or a structural support. Furthermore, in several alternative embodiments, the landing collars,  408 ,  610 , and  710 , of the systems,  400 ,  600  and  700 , include conventional anti-rotational locking devices and/or latching devices that further restrain the movement of the bottom cementing plugs,  416  and  622  after they engage the landing collars thereby improving the hydraulic seal between the bottom cementing plugs and the landing collars.  
         [0068]    Although illustrative embodiments of the invention have been shown and described, a wide range of modification, changes and substitution is contemplated in the foregoing disclosure. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Summary:
The present invention provides a cementing system and method for wellbores by cementing an annulus between a wellbore casing and a wellbore. In at least one embodiment, the invention includes a landing collar defining a restrictef passage, a wellbore casing defining a passage coupled to the landing collar, a top cementing plug for sealingly engaging the wellbore casing, a bottom cementing plug for sealingly engaging the wellbore casing, and a fluid injection assembly coupled to the wellbore casing for injecting fluidic materials into the wellbore casing and controllably releasing the top cementing plug includes a plug body defining a plug passage. a frangible membrane for sealing the plug passage, and a one-way valve for controlling the flow of fluidic materials through the plug passage. The invention also includes the bottom cementing plug and methods for operation.