Patent Publication Number: US-2003230405-A1

Title: System for running tubular members

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] The present application is a continuation-in-part of U.S. patent application Ser. No. 10/337,404 filed Jan. 6, 2003, which was a continuation of U.S. patent application Ser. No. 09/850,247 filed May 7, 2001, which was a continuation-in-part of U.S. patent application Ser. No. 09/829,107 filed Apr. 9, 2001, now U.S. Pat. No. 6,491,103. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to an apparatus for running tubular members such as drilling/production liners or subsea casing strings in a wellbore. More particularly the present invention relates to a wiper plug and internal drop ball mechanism that may be used in conjunction with the running and cementing of such tubular members in a wellbore.  
       [0004] 2. Description of the Prior Art  
       [0005] In oilfield applications, a “casing liner,” “drilling/production liner,” and a “subsea casing string” are tubular members which are run on drill pipe. The terms “casing liner” and “drilling/production liner” are usually used with respect to drilling operations on land, while the term “subsea casing string” is used with respect to offshore drilling operations. For ease of reference in this specification, the term “liner” is used to denote either a “casing liner,” a “drilling/production liner,” or a “subsea casing string.” 
       [0006] Prior art drop ball-actuated float equipment for use in cementing liners in place includes, for example, a float shoe or float collar which has one or more flapper valves and which is located at or near the bottom of the liner. The flapper valve or valves are conventionally held open by a breakable plastic tab which is actuated (i.e., broken) by a drop ball when the cementing operation is to begin. The industry has traditionally used systems where a drop ball is released at the surface, and the drop ball must be small enough in diameter to pass through the smallest restriction in the drill string, which usually is the diameter of the bore in the running tool. The size of such restrictions has, therefore, limited the maximum size of the opening in a float collar or shoe. In the case of a 13⅜″ liner, the maximum diameter of a drop ball is somewhere between 2 and 3 inches. Due to the small diameter bore of traditional float equipment and the highly contaminated environment in which such equipment is used, the valves in traditional float equipment tend to become plugged with cuttings and contaminants.  
       [0007] As a liner is lowered into the wellbore, the fluid in front of the liner must be displaced to flow through the opening in the float equipment as well as around the outside annulus defined by the wellbore and the liner. The flow resistance of the two flow paths may be high and thus causes a pressure known as surge pressure to build up below the liner. This surge pressure can: (a) cause damage to the formation; (b) result in loss of expensive drilling fluid; and (c) result in the liner sticking against the side of the borehole, which means the liner does not go to the bottom of the hole.  
       [0008] U.S. Pat. No. 5,960,881, which is incorporated herein by reference, discloses a downhole surge pressure reduction system to reduce the pressure buildup while running in a tubular member such as a casing liner. The system is typically located immediately above the top of the casing liner. Nonetheless, any plugging of the float equipment at the lower end of the casing liner can, and very well may, render the surge pressure reduction system of the &#39;881 patent ineffective.  
       [0009] The method and apparatus according to the present invention overcomes the plugging problem and allows enhanced passage of fluid through the tubular member and into the surge pressure reduction tool.  
       SUMMARY OF THE INVENTION  
       [0010] In accordance with the present invention, apparatus is provided for running a tubular member through a wellbore containing drilling fluid using a drill string.  
       [0011] Apparatus in accordance with the present invention comprises a running tool connected to the top of the tubular member having an axial bore therethrough.  
       [0012] Apparatus in accordance with the present invention further comprises a wiper plug assembly which includes a wiper plug releasably suspended from a running tool within the tubular member and a receptacle sleeve to receive a drill pipe dart. During cementing operations, the wiper plug assembly receives the drill pipe dart and is released from the drill string at the top of the tubular member. The wiper plug assembly is then pumped downward forcing cement out of the bottom of the tubular member and into the annulus between the tubular member and the borehole.  
       [0013] One end of the wiper plug assembly is connected to the running tool attached to the tubular member. The running tool for the wiper plug comprises an axially indexing sleeve and a plurality of wedge-shaped fingers which releasably engage the wiper plug receptacle sleeve. During running in of the tubular member, the drilling fluid flows from the tubular member upward through the ports between the fingers and into the void above the wiper plug fins. To isolate the wiper plug fins from internal pressure during cementing operations, the drill pipe sleeve is indexed axially downward to block the ports between the fingers.  
       [0014] Apparatus in accordance with the present invention also comprises a drop ball sub attached to and below the wiper plug assembly within the tubular member. The drop ball sub releases a float equipment actuator ball which is larger in diameter than the smallest restriction in the drill string. When released, the actuator ball drops to the bottom of the tubular member where it actuates float equipment. Once actuated, flapper valves in the float equipment prevent the back flow of cement traveling downward through the tubular member.  
       [0015] Apparatus in accordance with the present invention may further comprise a surge pressure reduction device or diverter tool connected between the drill string and the running tool. When the diverter tool is in an open port position, the drilling fluid may flow upward from inside the diverter tool into the annulus between the casing cemented in place and the drill string. When in a closed port position, the device provides passage for fluid to travel downward through the drill string.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016] In the accompanying drawings:  
     [0017]FIG. 1 is an elevation view of an, embodiment of the system of the present invention for running of a tubular member downhole.  
     [0018]FIG. 2 is an elevation view of an embodiment of the present invention illustrating flow path of the drilling fluid facilitating surge pressure reduction as tubular member is run downhole.  
     [0019]FIG. 3 is an elevation view of an embodiment of the present invention illustrating a drop ball seated in a yieldable seat of surge reduction apparatus with the ports of that apparatus in open position.  
     [0020]FIG. 4 is an elevation view of an embodiment of the present invention illustrating the surge reduction apparatus of FIG. 3 with the ports of that apparatus in closed position.  
     [0021]FIG. 5 is an elevation view of an embodiment of the present invention illustrating second drop ball seated in yieldable seat of a collet finger sleeve with the ports in open position.  
     [0022]FIG. 6 is an elevation view of an embodiment of the present invention illustrating the collet finger sleeve blocking the collet finger ports.  
     [0023]FIG. 7 is an elevation view of an embodiment of the present invention illustrating the drop ball seated in yieldable seat of a drop ball sub apparatus with the port of that apparatus in open position.  
     [0024]FIG. 8 is an elevation view of an embodiment of the present invention illustrating a flapper valve actuator ball being forced through a yieldable seat and drop ball sub apparatus with ports in closed position.  
     [0025]FIG. 9 is an elevation view of an embodiment of the present invention illustrating the flapper valve actuator ball engaging a float collar.  
     [0026]FIG. 10 is an elevation view of an embodiment of the present invention illustrating a drop ball being pressured through yieldable seat in the drop ball sub apparatus.  
     [0027]FIG. 11 is an elevation view of an embodiment of the present invention illustrating a dart being pumped downhole behind cement.  
     [0028]FIG. 12 is an elevation view of an embodiment of the present invention illustrating the dart of FIG. 11 being pumped downward through drill string and engaging a seat in a wiper plug assembly.  
     [0029]FIG. 13 is an elevation view of an embodiment of the present invention illustrating a wiper plug assembly being wound downward through a tubular member and forcing cement downward through float equipment, out of tubular member, and upwards into annulus between tubular member and formation.  
     [0030]FIG. 14A is an enlarged section view of the wiper plug assembly with collet fingers engaging wiper plug upper flange.  
     [0031]FIG. 14B is an enlarged section view of the dart engaging wiper plug assembly with collet fingers moving radially inward and releasing wiper plug.  
     [0032]FIG. 15 is an elevation view of an embodiment of the present invention illustrating a dual wiper plug apparatus.  
     [0033]FIG. 16 is an enlarged section view of the latching mechanism connecting the upper liner wiper plug to the lower liner wiper plug.  
     [0034]FIG. 17 is an enlarged section view of the latching mechanism as it releases the lower liner wiper plug from the upper liner wiper plug.  
     [0035]FIG. 18 is an elevation view of an embodiment of the present invention without an actuator ball sleeve illustrating flow path of the drilling fluid facilitating surge pressure reduction as tubular member is run downhole.  
     [0036]FIG. 19 is an elevation view of an embodiment of the present invention without an actuator ball sleeve illustrating the drop ball resting on the actuator ball with the collet finger sleeve blocking the collet finger ports.  
     [0037]FIG. 20 is an elevation view of an embodiment of the present invention without an actuator ball sleeve illustrating a flapper valve actuator ball being forced through a yieldable seat.  
     [0038]FIG. 21 is an enlarged section view of the four plug embodiment of the present invention illustrating the drop ball seated in yieldable seat of a drop ball sub apparatus with the port of that apparatus in open position.  
     [0039]FIG. 22 is an enlarged section view of the four plug embodiment of the present invention illustrating the drop ball seated in yieldable seat of a drop ball sub apparatus with the port of that apparatus in closed position.  
     [0040]FIG. 23 is an enlarged section view of the four plug embodiment of the present invention illustrating a dart being pumped downward through drill string and engaging a seat in the lower liner wiper plug assembly.  
     [0041]FIG. 24 is an enlarged section view of the four plug embodiment of the present invention illustrating the latching mechanism as it releases the lower liner wiper plug from the upper liner wiper plug and moving axially downward to engage the float equipment.  
     [0042]FIG. 25 is an enlarged section view of the four plug embodiment of the present invention illustrating actuator ball engaging the float equipment.  
     [0043]FIG. 26 is an enlarged section view of the four plug embodiment of the present invention illustrating the actuator ball activating the flapper valves of the float equipment.  
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION  
     [0044] A description of certain embodiments of the present invention is provided to facilitate an understanding of the invention. This description is intended to be illustrative and not limiting of the present invention. In the appended claims, the term “tubular member” is intended to embrace either a “casing liner,” a “subsea casing string,” or a “drilling/production liner.” 
     [0045] With reference first to FIG. 1, the general components of a system are illustrated in which apparatus in accordance with the present invention is used. A mast M suspends a traveling block TB. The traveling block, in turn, supports a top drive TD which moves vertically on a block dolly BD. An influent drilling fluid line L supplies the top drive TD with drilling fluid from a drilling fluid reservoir (not shown). A launching manifold LM connects to a drill string S. The drill string S comprises numerous pipes which extend down into the borehole BH, and the number of such pipes is dependent on the depth of the borehole BH. A flow diverting device B is connected between the bottom end of drill string S and the top of running tool  162 . A tubular member, such as casing liner  161 , is suspended from running tool  162 . Float equipment, e.g. float collar  160 , is fastened near the bottom of the casing liner  161 .  
     [0046] Solidified cement CE 1  fixes a surface casing SC to the surrounding formation F. The surface casing SC contains an opening O in the uppermost region of the casing adjacent to the top. The opening O controls return of drilling fluid as it travels up the annulus between the drill string S and the surface casing SC.  
     [0047] Solidified cement CE 2  fixes an intermediate casing IC to the surrounding formation F. The intermediate casing IC is hung from the downhole end of the surface casing SC by a mechanical or hydraulic hanger H.  
     [0048] The annulus between the drill string S and the intermediate casing IC is greater in area than the annulus between the casing liner  161  and the intermediate casing IC. While the present invention is not intended to be limited to use in tight or close clearance casing runs, the benefits of the present invention are more pronounced in tight clearance running, since as the area is reduced and the pressure (pressure is equal to weight/area) is increased.  
     [0049] Referring now to FIG. 2, apparatus in accordance with the present invention comprises running tool  162  which is connected to the top of casing liner  161  and which has an axial bore therethrough. In one embodiment of the present invention, a flow diverter tool B is removably connected between drill string S and running tool  162 , and in another embodiment of the present invention, no such diverter tool is employed. Diverter tool B, when used, is preferably a diverter device as disclosed in the &#39;881 patent. The diverter tool B comprises a housing  183  having at least one housing flow port  169 A, a yieldable seat  173 , and a sleeve  170  having at least one sleeve flow port  169 B. When diverter tool B is in the “open port position,” sleeve  170  is arranged such that housing flow port  169 A and sleeve flow port  169 B are aligned. This provides passage for drilling fluid to flow from inside of housing  183  to annulus between drill string S and the cemented in place casing  205 . When the diverter tool B is in the “closed port position,” sleeve  170  has been indexed axially downward so that housing flow port  169 A and sleeve flow port  169 B are not axially aligned and the flow passage is blocked.  
     [0050] Wiper plug assembly WP is suspended inside casing liner  161  from running tool  162  by the running tool S 2  for the wiper plug, one end of which is connected to running tool  162 . As described in U.S. patent application Ser. No. 09/541,526, file Apr. 3, 2000, the wiper plug WP is releasably connected to the second end of the running tool S 2  by collet fingers  168 . The openings or ports between collet fingers  168  provide communication to the void above wiper plug fins  163 . Drilling fluid flowing upward from drop ball sub  166  to flow diverter device B passes through the ports between collet fingers  168  and fills the void above wiper plug fins  163 . When casing liner  161  has been lowered to full depth, sleeve  171  may be indexed axially downward to block flow through the ports between collet fingers  168 , thereby isolating the wiper plug fins  163  from internal pressure.  
     [0051] Drop ball assembly DB is attached to the bottom of wiper plug assembly WP. The drop ball assembly DB comprises a housing  166  having at least one housing flow port  167 A, a yieldable seat  175 , a sleeve having at least one sleeve flow port  167 B, an actuator ball  201 , and a second yieldable seat  176 . Before the release of actuator ball  201 , sleeve  172  is arranged in the “open port position” such that housing flow port  167 A and sleeve flow port  167 B are aligned. These aligned ports provide a passage for drilling fluid to flow as discussed below.  
     [0052] Float equipment  160 , which may for example be a float collar, is located at or near the bottom of casing liner  161  and contains flapper valves which are actuated by the release of actuator ball  201 . The diameter of actuator ball  201  is greater than the smallest diameter in the drill string and corresponds to the diameter of the bore of the float equipment. The diameter of the bore of the float equipment is also greater than the smallest diameter in the drill string.  
     [0053] Still referring to FIG. 2, in operation, apparatus in accordance with one embodiment of the present invention is intended to be run down a borehole through drilling fluid while in the open port position. In the “open port position,” sleeve  170  of flow diverter device B (when used), sleeve  171  of wiper plug assembly WP, and sleeve  172  of drop ball sub DB are positioned such that drilling fluid may follow flow path FP upward through the bore of float equipment  160 . Following the flow path, drilling fluid then flows into the housing of drop ball sub DB above actuator ball  201  via aligned housing flow port  167 A and sleeve flow port  167 B, and through the bore in the wiper plug. Drilling fluid then fills the void above the wiper plug fins  163  via the openings between collet fingers  168 . The drilling fluid then flows through drill string S 2  and running tool  162 , into diverter device B, and finally out of diverter device B into the annulus between drill string S and the cemented-in-place casing  205  via aligned flow hole  169 A and flow port  169 B. The benefits of surge pressure reduction are thus provided.  
     [0054] In the embodiment of the present invention where no diverter tool is utilized, drilling fluid flows through drill string S 2  and running tool  162  and through drill string S.  
     [0055] Referring to FIG. 3, once the casing liner has been lowered to full depth and cementing operations are ready to begin, a drop ball  200  is dropped down drill string S and into yieldable seat  173  of flow diverter device B. If a diverter tool is not used, the first landing point for drop ball  200  is yieldable seat  174 . The diameter of drop ball  200  is less than the smallest diameter of any restriction in drill string S. For example, a 2¼ inch diameter drop ball may be used for a drill string with inside diameter of 3 inches.  
     [0056] Referring now to FIG. 4, drilling fluid is pressurized to a predetermined level above drop ball  200  such that sleeve  170  is moved axially downward blocking housing flow holes  169 A. The flow diverter device B is now in the “closed port position.” 
     [0057] Referring to FIG. 5, drilling fluid above drop ball  200  is further pressurized such that the yieldable seat  173  expands, and drop ball  200  passes through yieldable seat  173  and lands in yieldable seat  174  of collet finger sleeve  171 . Drilling fluid is then pressurized above drop ball  200  such that sleeve  171  is moved axially downward which closes the ports formed by the spaces between collet fingers  168  as illustrated in FIG. 6.  
     [0058] Referring to FIG. 7, drilling fluid above drop ball  200  is further pressurized such the yieldable seat  174  expands and drop ball  200  passes through expanded yieldable seat  174  and lands in seat  175  of drop ball sub  176 . Drilling fluid is then pressurized to a predetermined level above drop ball  200  such that sleeve  172  is moved axially downward. As sleeve  172  moves downward, the sleeve engages float valve actuator ball  201  and forces the ball through yieldable seat  176  as illustrated in FIG. 8.  
     [0059] With reference to FIG. 9, the float valve actuator ball  201  is released from drop ball sub  166  and moves downward toward the bottom of casing liner  161  where ball actuates flapper valves of float equipment  160 . Float valve actuator ball  201  then continues to bottom of casing liner  161  and exits casing liner  161  where it may subsequently be grinded into filings by downhole drill equipment.  
     [0060] With reference to FIG. 10, drilling fluid above drop ball  200  is further pressurized such that yieldable seat  175  is expanded and drop ball  200  passes through the expanded seat  175 , and exits casing liner where it may subsequently be grinded into filings by downhole drill equipment. At this time, the cementing operations are ready to commence.  
     [0061] With reference to FIG. 11, once cement pumping is complete, a drill pipe dart  202  is inserted into top of drill string S and displaced downward by drilling fluid so that dart  202  establishes a barrier between drilling fluid and cement CE 3 . With reference to FIGS. 12 and 14A, once the dart  202  reaches wiper plug assembly WP, the dart engages a receptacle sleeve  182 . The dart  202  conventionally comprises a nose section with a barbed “shark tooth” profile “c-ring” for connection with receptacle sleeve  182  and elastomer o-ring seals. The receptacle sleeve  182  comprises a mating tooth profile for connection with the dart  202  and a seal bore for receiving the O-rings. In this way, the dart  202  and receptacle sleeve  182  form a sealed mechanical connection.  
     [0062] With reference to FIGS. 13 and 14B, a yieldable, disk-shaped flat washer  181  supports dart receptacle sleeve  182  in the wiper plug assembly WP. Flat washer  181  is mounted in such a way that force imparted by dart  202  is carried through the washer  181 . As drilling fluid is further pressured above dart  202 , the flat washer  181  yields and deflects slightly downward. The deflection of the flat washer  181  allows the receptacle sleeve  182  to move slightly downward. The dart receptacle sleeve  182  serves as a backup to collet fingers  168  formed on the end of the drill string S 2 . The collet fingers  168  are formed such that their lower outer ends comprise wedge surfaces  179 A, which are captured in a mating recess  179 B in the top flange portion of the wiper plug assembly WP. As the dart receptacle sleeve  182  displaces downward due to the pressure above the dart  202 , the radial support for the collet fingers  168  is lost. The loss of radial support allows the wedge surfaces  179 A to force the collet fingers  168  radially inward thereby releasing the wiper plug assembly WP from the drill string S 2 .  
     [0063] With reference still to FIG. 13, once released from drill string S 2 , the wiper plug WP maybe pumped down the casing liner  161  thereby displacing cement CE 3  in the casing liner down through the flapper valves of float equipment  60 . The flapper valves of the float equipment  160  should prevent any “back-flow” or “u-tube action” of the cement.  
     [0064] Once the wiper plug WP has been pumped to the bottom of the casing liner, the cement is allowed to harden, thereby completing the hanging and cementing job.  
     [0065] In another embodiment of the present invention, the drop ball sub is used to launch an actuator ball without the sliding sleeve  172  (FIG. 2). Referring to FIG. 18, the drop ball assembly DB is attached to the bottom of wiper plug assembly WP and comprises a housing  166  having a set of housing flow holes  167 A, an actuator ball  201 , and a yieldable seat  176 . The set of housing flow holes  167 A are sized to permit the creation of a pressure differential between the annular space within the housing  166  and the space outside the housing when drilling fluid pressure is increased above the actuator ball  201  to launch the actuator ball through the yieldable seat  176 . In a preferred embodiment, the set of housing flow holes comprises four holes of 1 inch diameter size such that the actuator ball may be launched at a pressure differential of approximately 100 psi. However it is intended that the holes may be sized to accommodate whatever pressure differential is required to launch the actuator ball.  
     [0066] With reference to FIG. 19, once drop ball  200  is used to move the sleeve  171  axially downward to close the ports formed by the spaces between collet fingers  168 , drilling fluid above drop ball  200  is further pressurized such that the yieldable seat  174  expands and drop ball  200  passes through expanded yieldable seat  174 . The drop ball  200  lands on top of the actuator ball  201  within the drop ball housing  166  thus creating a clear bore through drill string S 2 . Drilling fluid is then pressurized to a predetermined level above actuator ball  201  such that the actuator ball is forced through yieldable seat  176  as illustrated in FIG. 20. This is accomplished by pumping drilling fluid from the drill string into the drop ball housing  166  at a rate greater than the rate at which the drilling fluid can exit the housing via the set of flow ports  167 A. This creates a pressure differential where the drilling fluid pressure is greater within the drop ball housing  166  than in the annular space between the drop ball housing and the casing liner  161 . When the drilling fluid pressure differential within the drop ball housing  166  is increased to a predetermined level, the yieldable seat yields to launch the actuator ball from the drop ball housing. In a preferred embodiment, the yieldable seat  176  of the drop ball housing  166  is fabricated to yield at a pressure differential of approximately 100 psi.  
     [0067] With reference to FIG. 20, the float valve actuator ball  201  is released from drop ball sub DB and moves downward toward the bottom of casing liner  161  where ball actuates the flapper valves FC 2  of float equipment  160  as illustrated in FIG. 10. Float valve actuator ball  201  and drop ball  200  then continue to bottom of casing liner  161  and exit casing liner where they may subsequently be grinded into filings by downhole drill equipment. At this time, the cementing operations are ready to commence.  
     [0068] The foregoing has described what may be referred to as a “two plug system” having one wiper plug and one dart which is used in the release of the wiper plug. With reference to FIG. 15, another embodiment of the present invention comprises an upper liner wiper plug WP 1  and a lower liner wiper plug WP 2 . This type of system may be referred to as a “four plug system” since it comprises two wiper plugs and two drill pipe darts to release the wiper plugs.  
     [0069] The four plug system of FIG. 15 operates in substantially the same way as the two plug system. In both the two plug system and the four plug system, the apparatus is first run down a borehole until it reaches the required depth to hang a casing liner. At this depth, a drop ball is pumped down the drill string into yieldable seat of drop ball sub. Drilling fluid pressure is increased behind the drop ball to release an actuator ball from the drop ball sub to activate flapper valves of float collar.  
     [0070] With reference to FIG. 15, the four plug system comprises an upper liner wiper plug WP 1  attached to drill string DS, a lower liner wiper plug WP 2  attached to the upper liner wiper plug by release mechanism (see FIG. 16), and a drop ball sub DB attached to the bottom of the lower liner wiper plug.  
     [0071] With reference to FIGS. 15 and 17, after the flapper valve actuator ball  310  is released, a first drill string dart  400  is pumped down the drill string and into casing liner CL where the first dart engages a lower liner wiper plug WP 2 . Drilling fluid pressure is increased above the first dart  400  so that the lower liner wiper plug WP 2  is released from an upper liner wiper plug WP 1  and is pumped downward through the casing liner CL to displace contaminating drilling mud from the interior of the casing liner. At the bottom of the casing liner CL, drilling fluid pressure is further increased above the first dart  400  so that the lower liner wiper plug latches to the float collar FC. Next, cement is pumped downward through the casing liner CL and into the annulus between the borehole and the casing liner. Then, a second drill string dart (not shown) is pumped down the drill string and into the casing liner CL where the second dart engages an upper liner wiper plug WP 1 . Drilling fluid pressure is increased above the second dart so that the upper liner wiper plug WP 1  is released from the drill string DS and is pumped downward through the casing liner CL to displace cement from the interior of the casing liner. At the bottom of the casing liner CL, drilling fluid pressure is again increased above the second dart so that the upper liner wiper plug WP 1  latches to the lower liner wiper plug WP 2 .  
     [0072] With reference to FIG. 16, the release mechanism for releasing lower liner wiper plug WP 2  from upper liner wiper plug WP 1  comprises lower liner fingers  301  having wedge-shaped ends  301 A, upper liner finger receivers  300  having wedge-shaped recesses  300 A, a lower liner dart receptacle  302 , and a sleeve  303  having radial protrusions  303 A. Initially, the wedge-shaped ends  301 A of lower liner fingers  301  engage the wedge-shaped recesses  300 A of upper liner fingers  300 . The protrusions  303 A of sleeve  303  prevent the lower liner fingers  301  from moving radially inward and lock the wedge shaped-ends  301 A in the wedge-shaped recesses  300 A. The sleeve  303  is itself restrained by shear pins  304 .  
     [0073] With reference to FIG. 17, a drill pipe dart  400 , having a diameter less than the diameter of upper liner receptacle  305 , is dropped into the drill string and lands in lower liner dart receptacle  302 . Drilling fluid pressure is increased above dart  400  to shear pins  304  (shown in FIG. 16). Sleeve  303  is now unrestrained. Drilling fluid pressure is further increased above dart  400  to push sleeve  303  downward so that protrusions  303 A move below wedge-shaped ends  301 A of lower liner fingers  301 . The lower liner fingers  301  are now free to move radially inward to disengage with wedge-shaped recesses  300 A of upper liner fingers  300 . Drilling fluid pressure above dart  400  is increased to pump the released lower liner wiper plug WP 2  downward displacing drilling mud from the inside walls of the casing liner CL. Once the lower liner wiper plug WP 2  reaches the bottom of the casing liner CL, drilling fluid pressure is further increased above the dart  400  to latch the lower liner wiper plug to float collar FC (shown in FIG. 15). Cementing operations may then be commenced.  
     [0074] With reference to FIG. 15, the upper liner wiper plug WP 1  may then be released from the drill string DS by following the same procedure described above to release wiper plug WP (shown in FIGS. 12, 13,  14 A, and  14 B) in the two plug system. Once the upper liner wiper plug WP 1  is pumped to the bottom of the casing liner CL and is latched to the lower liner wiper plug WP 2 , the cement is allowed to harden, thereby completing the hanging and cementing job.  
     [0075] In another embodiment of the four plug system, before the float equipment is activated, the lower liner wiper plug assembly is pumped downward such that the drop ball sub engages the float equipment and then releases the actuator ball to activate the flapper valves of the float equipment. Referring to FIG. 21, before the release of the lower liner wiper plug WP 2 , a drop ball  403  is dropped from the drill string into the yieldable seat  401  of the sliding sleeve  402 . Drilling fluid is then pressurized to a predetermined level above drop ball  403  such that sleeve  402  is moved axially downward blocking the set of housing flow holes  167 A. The drop ball sub DB is now in the “closed port position” (as shown in FIG. 22). Drilling fluid pressure is increased above the drop ball  403  such that the seat  401  yields thereby permitting the drop ball to pass through and land on the actuator ball  201 . Cementing operations can now commence.  
     [0076] With reference to FIG. 23, after the drop ball sub DB is set to the closed port position, a first drill string dart  400  is pumped down the drill string by cement and into casing liner CL where the first dart engages a lower liner wiper plug WP 2 . Cement pressure is increased above the first dart  400  so that the lower liner wiper plug WP 2  is released from an upper liner wiper plug WP 1  and is pumped downward through the casing liner CL to displace contaminating drilling mud from the interior of the casing liner. At the bottom of the casing liner CL, cement pressure is further increased above the first dart  400  so that the lower liner wiper plug latches to the float collar FC.  
     [0077] Referring to FIG. 24, cement pressure is again increased to a predetermined level above the first dart  400  to release the first dart  400  from engagement with the lower liner wiper plug WP 2 . The dart  400  lands in the drop ball sub DB near the drop ball  403  and above the actuator ball  201 .  
     [0078] Referring to FIG. 25, cement pressure is increased to a predetermined level above the actuator ball  201  to launch the actuator ball from the drop ball sub DB into the axial bore of the float collar FC. The actuator ball  201  lands in the seat FC 3  of the actuating sleeve FC 1  of the float collar FC.  
     [0079] Referring to FIG. 26, cement pressure is again increased to a predetermined level above the actuator ball  201  to displace the actuating sleeve FC 1  from the bore of the float collar FC thus allowing the flapper valves FC 2  of the float collar to activate to any back-flow of the cement. The upper liner wiper plug is released and the cementing job is completed as described above.