Moled foam plugs, plug systems and methods of using same

Abstract

The present invention is directed to plugs, plug systems and methods for using the plugs and systems in subterranean wells. The plugs comprise an inner mandrel and an outer sleeve formed of a compressible foam. The plug systems include an assembly comprising a top plug and a bottom plug having foam outer sleeves. The plug systems further comprise a float valve into which the assembly fits. In the method, the bottom plug is deployed ahead of the top plug to separate a second fluid from a first fluid and wipe the inside of the pipe string clean of the first fluid. The top plug is used to wipe the inside of the pipe string clean of the second fluid and stop the displacement of the second fluid into the annulus between the casing string and the well bore.

1 . A plug for separating fluids successively introduced into a wellbore comprising an inner mandrel and an outer foam sleeve secured thereto.  
   
   
       2 . The plug according to  claim 1  wherein the inner mandrel is generally cylindrical in shape having an upper and lower end and has a hollow inner passage through which fluids may pass.  
   
   
       3 . The plug according to  claim 2  wherein a nose is attached to the lower end of the inner mandrel.  
   
   
       4 . The plug according to  claim 3  wherein a recess is formed within the nose of the inner mandrel and the plug further comprises an elastomeric flat face seal ring disposed therein.  
   
   
       5 . The plug according to  claim 2  wherein a recess is formed within the upper end of the inner mandrel  
   
   
       6 . The plug according to  claim 5  wherein a high pressure disc is secured within the recess of the upper end of the inner mandrel.  
   
   
       7 . The plug according to  claim 5  wherein a rupturable member is secured within the recess formed within the upper end of the inner mandrel.  
   
   
       8 . The plug according to  claim 2  further comprising a rupture disc for selectively allowing fluid flow through the inner passage.  
   
   
       9 . The plug according to  claim 1  wherein the outer foam sleeve is generally cylindrical in shape and has a hollow inner passage inside of which the inner mandrel is coaxially disposed and bonded thereto.  
   
   
       10 . The plug according to  claim 1  wherein the outer foam sleeve comprises a compressible open-cell foam.  
   
   
       11 . The plug according to  claim 1  wherein the inner mandrel comprises a drillable material.  
   
   
       12 . The plug according to  claim 1  wherein the outer foam sleeve comprises a plurality of ribs.  
   
   
       13 . The plug according to  claim 1  wherein the inner mandrel is formed of a solid drillable material.  
   
   
       14 . The plug according to  claim 1  wherein a nose is attached to an end of the inner mandrel.  
   
   
       15 . The plug according to  claim 14  wherein the nose is threadably attached to the end of the inner mandrel.  
   
   
       16 . The plug according to  claim 14  wherein the nose has holes formed in an inner surface for receiving pins.  
   
   
       17 . The plug according to  claim 16  further comprising a fluid stopper plug disposed within the nose and secured thereto by pins held within the holes.  
   
   
       18 . The plug according to  claim 17  further comprising at least one elastomeric ring disposed between the fluid stopper plug and the inner surface of the nose, which creates a fluid seal therebetween.  
   
   
       19 . The plug according to  claim 1  wherein the inner mandrel has a funnel-shaped upper end adapted to receive a taper-shaped nose from an adjacent plug.  
   
   
       20 . A plug system for separating fluids successively introduced into a passage comprising an assembly of at least two plugs wherein at least one of the plugs comprises an inner mandrel and an outer foam sleeve secured thereto.  
   
   
       21 . The plug system for separating fluids according to  claim 20  wherein the assembly comprises two plugs each of which comprises an inner mandrel and an outer foam sleeve secured thereto.  
   
   
       22 . The plug system for separating fluids according to  claim 21  wherein the two plugs are linearly aligned in a top and bottom configuration.  
   
   
       23 . The plug system for separating fluids according to  claim 22  wherein the inner mandrel of each of the plugs is generally cylindrical in shape having an upper and lower end and has a hollow inner passage through which fluids may pass.  
   
   
       24 . The plug system for separating fluids according to  claim 23  wherein a nose is attached to the lower end of each inner mandrel.  
   
   
       25 . The plug system for separating fluids according to  claim 24  wherein a recess is formed within the nose of each inner mandrel and each plug further comprises an elastomeric flat face seal ring disposed within each such recess.  
   
   
       26 . The plug system for separating fluids according to  claim 25  wherein a recess is formed within the upper end of the inner mandrel of each plug.  
   
   
       27 . The plug system for separating fluids according to  claim 26  wherein at least part of the upper end of the inner mandrel of the bottom plug is adapted to mate with the nose of the top plug.  
   
   
       28 . The plug system for separating fluids according to  claim 26  wherein a high pressure disc is secured within the recess formed within the upper end of the inner mandrel of the top plug.  
   
   
       29 . The plug system for separating fluids according to  claim 26  wherein a rupturable member is secured within the recess formed within the upper end of the inner mandrel of the bottom plug.  
   
   
       30 . The plug system for separating fluids according to  claim 26  further comprising a float valve.  
   
   
       31 . The plug system for separating fluids according to  claim 30  wherein the nose of the bottom plug mates with the float valve.  
   
   
       32 . The plug system for separating fluids according to  claim 20  wherein the outer foam sleeve of the at least one plug is generally cylindrical in shape and has a hollow inner passage inside of which the inner mandrel is coaxially disposed and bonded thereto.  
   
   
       33 . The plug system for separating fluids according to  claim 20  wherein the outer foam sleeve of the at least one plug comprises a compressible open-cell foam.  
   
   
       34 . The plug system for separating fluids according to  claim 20  wherein the inner mandrel of the at least one plug comprises a drillable material.  
   
   
       35 . The plug system for separating fluids according to  claim 20  wherein the outer sleeve of the at least one plug comprises ribs.  
   
   
       36 . The plug system for separating fluids according to  claim 22  wherein the top plug comprises an inner mandrel having an upper and lower end with a taper-shaped nose attached at the lower end and the bottom plug comprises an inner mandrel having an upper and lower end with a nose attached at the lower end and a funnel-shaped recess formed at the upper end for engagement with the nose of the top plug.  
   
   
       37 . The plug system for separating fluids according to  claim 36  wherein the inner mandrel of the top plug is formed of a solid material and the inner mandrel of the bottom plug is tubular-shaped.  
   
   
       38 . The plug system for separating fluids according to  claim 37  wherein the nose of the top plug is threadably attached to the lower end of the solid inner mandrel and the nose of the bottom plug is integrally formed with the lower end of the tubular-shaped inner mandrel.  
   
   
       39 . The plug system for separating fluids according to  claim 38  further comprising a fluid flow stopper secured within the nose of the bottom plug.  
   
   
       40 . The plug system for separating fluids according to  claim 39  wherein the outer sleeves of the top and bottom plugs comprise ribs.  
   
   
       41 . The plug system for separating fluids according to  claim 36  wherein both inner mandrels are tubular-shaped defining internal flow channels.  
   
   
       42 . The plug system for separating fluids according to  claim 41  wherein the nose of the top plug is taper-shaped and integrally formed with the lower end of the inner mandrel and the nose of the bottom plug is taper-shaped and integrally formed with lower end of the tubular-shaped inner mandrel.  
   
   
       43 . The plug system for separating fluids according to  claim 42  further comprising fluid flow stoppers having adjustable release pressures secured within each of the noses of the top and bottom plugs.  
   
   
       44 . The plug system for separating fluids according to  claim 43  wherein the outer sleeves of the top and bottom plugs comprise ribs.  
   
   
       45 . A method of separating fluids successively introduced into a subterranean well bore, comprising the steps of: 
 suspending an assembly comprising a plurality of plugs within a casing string, wherein at least one of the plugs comprises an inner mandrel and an outer foam sleeve secured thereto introducing a first fluid into the well bore through the casing string;    introducing a second fluid into the well bore behind the first fluid such that an interface between the two fluids is formed; and    deploying the at least one plug within the casing string at the interface of the first and second fluids.    
   
   
       46 . The method of separating fluids according to  claim 45  further comprising the step of installing a float valve within the casing string proximate the deepest part of the well bore.  
   
   
       47 . The method of separating fluids according to  claim 45  wherein the assembly comprises two plugs linearly aligned in a top to bottom configuration and wherein both the top and bottom plugs comprise an inner mandrel and outer foam sleeve secured thereon.  
   
   
       48 . The method of separating fluids according to  claim 47  wherein the inner mandrel of each of the plugs is generally cylindrical in shape has an upper and lower end and has a hollow inner passage through which fluids may pass.  
   
   
       49 . The method of separating fluids according to  claim 48  wherein a nose is attached to the lower end of each inner mandrel.  
   
   
       50 . The method of separating fluids according to  claim 49  wherein a recess is formed within the nose of each plug and each plug further comprises an elastomeric flat face seal ring formed therein.  
   
   
       51 . The method of separating fluids according to  claim 50  wherein a recess is formed within the upper end of each plug.  
   
   
       52 . The method of separating fluids according to  claim 51  wherein at least part of the upper end of the inner mandrel of the bottom plug is adapted to mate with the nose of the top plug.  
   
   
       53 . The method of separating fluids according to  claim 52  wherein a high pressure disc is secured within the recess formed within the upper end of the inner mandrel of the top plug.  
   
   
       54 . The method of separating fluids according to  claim 53  wherein a rupturable member is secured within the recess formed within the upper end of the inner mandrel of the bottom plug.  
   
   
       55 . The method of separating fluids according to  claim 54  wherein the bottom plug is deployed at the interface of the first and second fluids and wipes an inside surface of the casing string clean of the first fluid as it travels down the casing string.  
   
   
       56 . The method of separating fluids according to  claim 55  wherein once the bottom plug reaches the float valve the nose of the bottom plug mates with the float valve.  
   
   
       57 . The method of separating fluids according to  claim 56  wherein the second fluid is pumped down the casing string under pressure until the rupturable member fails.  
   
   
       58 . The method of separating fluids according to  claim 57  wherein the top plug is released behind the second fluid and travels down the casing string wiping the inside surface of the casing string clean of the second fluid.  
   
   
       59 . The method of separating fluids according to  claim 58  wherein the top plug engages with the bottom plug at the float valve.  
   
   
       60 . The method of separating fluids according to  claim 59  wherein approximately all of the second fluid has completely filled an annulus disposed between the casing string and the well bore at the point at which the top plug engages the bottom plug.  
   
   
       61 . The method of separating fluids according to  claim 60  wherein the first fluid is a drilling fluid and the second fluid is a cement slurry.  
   
   
       62 . The method of separating fluids according to  claim 61  further comprising the step of drilling the plugs out of the casing string after the cement slurry has cured.  
   
   
       63 . The method of separating fluids according to  claim 47  wherein the top plug comprises an inner mandrel having an upper and lower end with a taper-shaped nose attached at the lower end and the bottom plug comprises an inner mandrel having an upper and lower end with a nose attached at the lower end and a funnel-shaped recess formed at the upper end for engagement with the nose of the top plug.  
   
   
       64 . The method of separating fluids according to  claim 63  wherein the inner mandrel of the top plug is formed of a solid material and the inner mandrel of the bottom plug is tubular-shaped.  
   
   
       65 . The method of separating fluids according to  claim 64  wherein the nose of the top plug is threadably attached to the lower end of the solid inner mandrel and the nose of the bottom plug is integrally formed with the lower end of the tubular-shaped inner mandrel.  
   
   
       66 . The method of separating fluids according to  claim 65  further comprising a fluid flow stopper secured within the nose of the bottom plug.  
   
   
       67 . The method of separating fluids according to  claim 47  wherein the outer sleeves of the top and bottom plugs comprise ribs.  
   
   
       68 . The method of separating fluids according to  claim 47  wherein both inner mandrels are tubular-shaped defining internal flow channels.  
   
   
       69 . The method of separating fluids according to  claim 68  wherein the nose of the top plug is taper-shaped and integrally formed with the lower end of the inner mandrel and the nose of the bottom plug is taper-shaped and integrally formed with lower end of the tubular-shaped inner mandrel.  
   
   
       70 . The method of separating fluids according to  claim 69  further comprising fluid flow stoppers having adjustable release pressures secured within each of the noses of the top and bottom plugs.  
   
   
       71 . The method of separating fluids according to  claim 70  wherein the outer sleeves of the top and bottom plugs comprise ribs.