Patent Publication Number: US-6712145-B2

Title: Float collar

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 09/951,828 filed on Sep. 11, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to apparatus for use in the oil industry, and, more particularly, to a float collar apparatus for use in oil well drilling operations. 
     2. Description of the Prior Art 
     Float collars are utilized by the oil well industry with respect to operations for running in and cementing casing liners down a wellbore. An example of a prior art float collar is the Multi-Purpose Float Collar manufactured and sold by Davis-Lynch, Inc. The Multi-Purpose Float Collar comprises a tubular housing having a bore therethrough and two spring-activated flapper valves which are held in an open position by a sliding sleeve installed in the bore of the float collar. Once the sleeve is forced out of the bore of the float collar, the spring-activated flapper valves are free to rotate to their closed positions. 
     In practice, a float collar, such as the Multi-Purpose Float Collar of Davis-Lynch, Inc., is installed within the lower end of a casing liner prior to running the casing liner down a wellbore. When the spring-activated flapper valves of the float collar are held in an open position by the sliding sleeve, a clear passage is provided through the casing liner. This open position permits drilling fluid to flow freely through the float collar as the casing liner is being run downhole, which helps to reduce surge pressure against the borehole walls and permits the casing liner to be more readily lowered to total depth. Additionally, if a tight hole condition is encountered during running in of the casing liner, drilling fluid can be pumped downward through the casing liner to circulate drilling fluid around the tight hole condition thereby freeing the casing liner. 
     Once the casing liner is lowered to total depth, the sliding sleeve of the float collar is actuated using a drop ball, which seats in a ball seat which is coupled to the sliding sleeve. The sliding sleeve is held in place by shear pins installed in the lower portion of the sleeve. Pressure is then increased above the drop ball until the shear pins shear, at which time the sleeve is displaced axially out of the float collar. This movement of the sleeve frees the spring-activated flapper valves to rotate to a closed position. In the closed position, the flow path through the casing liner is obstructed such that any fluid passing through the casing liner must overcome the resistance of the spring-activated flapper valves to establish communication between the lower end of the casing liner and the annulus between the casing liner and the borehole. 
     During cementing operations, cement is pumped downward through the casing liner at sufficiently high pressure to overcome the resistance of the spring-activated flapper valves. Once cement pumping operations cease, the spring-activated flapper valves close and seal the passage through the casing liner. This prevents the cement from flowing back upward into the casing liner. This effect is also known in the art as “back-flow” or “u-tube” action. Finally, once cementing operations are completed, the entire float collar assembly is drilled out of the casing liner to reestablish an unobstructed flow path through the wellbore. 
     While prior art float collars have produced desirable results for the oil well industry, an undesirable feature of prior art float collars is that once cementing operations are complete, prior art float collars require approximately six hours to drill out of the casing liner to reestablish the unobstructed flow path. This relatively long drill out time is due in large part to the high metal content of components of the float collar. Prior art float collars are fabricated almost entirely of metals, e.g. aluminum. While the use of such metals allows the float collar assembly to be set at pressures up to 3000 psi, the metal components of the float collar assembly become a disadvantage when cementing operations are completed and valuable time and resources must be expended during drilling out the float collar. 
     Accordingly, it would be desirable to have a float collar which can be drilled out in substantially less time than prior art float collars. This novel and useful result has been achieved by the present invention. 
     SUMMARY OF THE INVENTION 
     Apparatus in accordance with the present invention comprises a float collar assembly for regulating the passage of fluid through a tubular member, such as a casing liner. The float collar assembly is positioned within the tubular member cased in cement at the lower end of the tubular member. 
     In a first embodiment of the present invention, a float collar assembly comprises an outer housing having an axial bore therethrough and one or more spring-activated flapper valves arranged within the housing. The spring-activated flapper valves are activated by an internal valve-actuating sleeve which is fabricated from a hardened plastic material. Such hardened plastic material may include a modified nylon blend material, such as cast type 6 nylon having enhanced thermal-resistant, weather-resistant, and bearing properties, or a nylon-phenolic laminate. The actuating sleeve is initially held inside the housing by a connecting means. While the actuating sleeve is connected to the housing, the spring-activated flapper valves are secured by the actuating sleeve in an open position. A drop ball seat is integral with the actuating sleeve and is located at the bottom of the actuating sleeve. The seat receives a drop ball thereby creating a seal which blocks fluid flow through the tubular member. Subsequently, fluid pressure is increased above the drop ball seat to activate the connecting means to release the actuating sleeve and displace the actuating sleeve downward from the housing. Once the actuating sleeve is displaced from the housing, the spring-activated flapper valves are free to rotate to a closed position. In the closed position, the spring-activated flapper valves obstruct passage through the tubular member. 
     In another embodiment of the present invention, the connecting means is a set of shear pins which connect the actuating sleeve to the housing. When the connecting means is activated by the drop ball, the set of shear pins is sheared. Once the set of shear pins is sheared, the actuating sleeve is free to displace axially downward out of the housing. 
     In still another embodiment of the present invention, the connecting means is a shoulder formed on the upper end of the actuating sleeve which protrudes radially outward and a groove formed in the axial bore of the housing. Initially, the shoulder of the actuating sleeve engages the groove of the housing to connect the actuating sleeve to the housing. When the connecting means is activated, the shoulder of the actuating sleeve is sheared by the groove of the housing. Once the shoulder is sheared, the actuating sleeve is free to displace axially downward out of the housing. 
     In yet another embodiment of the present invention, the connecting means is a lightweight metal shearing sleeve attached to the upper end of the actuating sleeve having a shoulder formed on the upper end of the shearing sleeve which protrudes radially outward and a groove formed in the axial bore of the housing. The shoulder of the shearing sleeve engages the groove of the housing to connect the actuating sleeve to the housing. The connecting means also includes a recess formed between the upper end and lower end of the shearing sleeve such that thickness of the wall of the shearing sleeve is smallest at the recess. When the connecting means is activated, the shearing sleeve is sheared at the recess at a predetermined pressure. Once the shearing sleeve is sheared, the actuating sleeve is free to displace axially downward out of the housing. 
     Furthermore, while components of prior art float collars are fabricated almost entirely from metal, the float collar apparatus of the present invention is fabricated from a combination of metal and non-metal components, or from non-metal components only. This resultant float collar assembly provides a savings in time and resources expended during drilling out of the float collar. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a profile view of a float collar in accordance with the present invention for regulating the position of spring-activated flapper valves in an oil well casing liner. 
     FIG. 2 is an enlarged section view of a first embodiment of a float collar in accordance with the present invention with actuating sleeve in place securing spring-activated flapper valves in an open position. 
     FIG. 3 is an enlarged section view of a first embodiment of a float collar in accordance with the present invention with drop ball lodged in seat of actuating sleeve. 
     FIG. 4 is an enlarged section view of a first embodiment of a float collar in accordance with the present invention with actuating sleeve displaced downward from float collar housing and spring-activated flapper valves rotated to closed position. 
     FIG. 5 is an enlarged section view of a second embodiment of a float collar in accordance with the present invention with actuating sleeve in place securing spring-activated flapper valves in an open position. 
     FIG. 6A is an enlarged section view of a second embodiment of a float collar in accordance with the present invention with a drop ball seated in drop ball seat of actuating sleeve. 
     FIG. 6B is an enlarged section view of a second embodiment of a float collar in accordance with the present invention with actuating sleeve being displaced axially downward. 
     FIG. 6C is an enlarged section view of a second embodiment of a float collar in accordance with the present invention with actuating sleeve displaced completely downward from float collar housing and spring-activated flapper valves rotated to closed position. 
     FIG. 7A is an elevation view of an embodiment of the actuating sleeve being fabricated from a phenolic-nylon laminate and having an aluminum shearing sleeve attached to the top. 
     FIG. 7B is an elevation view of the actuating sleeve of FIG. 7A with a drop ball seated in drop ball seat of actuating sleeve and depicting the aluminum shearing sleeve being sheared. 
     FIG. 8A is an elevation view of an embodiment of the actuating sleeve being fabricated from a phenolic-nylon laminate. 
     FIG. 8B is a sectional view of the actuating sleeve of FIG. 8A depicting each layer of the phenolic-nylon laminate. 
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     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. The preferred embodiment of the float collar of the present invention will be described with respect to installation of an oil well casing liner. The term “casing liner” is referred to throughout this application and is intended to mean a “drilling/production liner” or a “sub-sea casing.” However, it is intended that the present invention may be utilized with any tubular member being run in and cemented in a wellbore. 
     With reference to FIG. 1, an apparatus in accordance with the present invention includes a float collar assembly  100  held in place by cement  300  at the lower end of tubular member  200 . 
     With reference to FIG. 2, a first embodiment of a float collar assembly  100 A in accordance with the present invention includes a housing  101 , two flapper valve assemblies  114 A,  114 B, and a valve-actuating sleeve  120 . Each flapper valve assembly  114 A,  114 B includes a flapper  110 A,  110 B, a flapper recess  112 A,  112 B, a pin and spring  111 A,  111 B, and a frustoconical valve body  113 A,  113 B. The actuating sleeve  120  includes a drop ball seat  122  integral with the inner surface of the actuating sleeve and having an axial bore therethrough for receiving a drop ball  130  (FIG.  3 ). The diameter of the drop ball  130  (FIG. 3) is less than or equal to diameter of the actuating sleeve  120 , but greater than diameter of the axial bore of the drop ball seat  122 . Additionally, the actuating sleeve  120  includes a plurality of pin recesses  123  for receiving a plurality of shear pins  121 . The pin recesses  123  are formed along the outer surface and near the upper end of the actuating sleeve  120 . 
     Still with reference to FIG. 2, in operation, the first embodiment of a float collar apparatus in accordance with the present invention is installed within the lower end of a casing liner  200  (FIG. 1) with the actuating sleeve  120  holding the flappers  110 A,  110 B of the flapper valve assemblies  114 A,  114 B in an open position against the tension of the flapper springs  111 A,  111 B. The actuating sleeve  120  is restrained from axial displacement by the shear pins  121  installed in the pin recesses  123  of the actuating sleeve. An open flow path exists through the float collar and the drilling fluid can pass unobstructed through the axial bore of housing  101 . 
     With reference to FIG. 3, once the casing liner  200  (FIG. 1) is lowered to total depth, a drop ball  130  is dropped down the casing liner, through the upper end of the housing  101 , and into the drop ball seat  122 . The drop ball  130  seals with the drop ball seat  122  thereby obstructing the flow path of drilling fluid through the casing liner  200  (FIG.  1 ). 
     Next, with reference to FIG. 4, drilling fluid pressure is increased above the drop ball  130  and the drop ball seat  122  to a predetermined level such that the shear pins  121  shear. With the shear pins  121  sheared, the actuating sleeve  120  is free to displace axially downward out of the housing  101  to the bottom of the borehole. Once the actuating sleeve  120  is displaced from the housing  101 , the flappers  110 A,  110 B of the flapper valve assemblies  114 A,  114 B are forced by the springs  111 A,  111 B to rotate into engagement with the frustoconical valve bodies  113 A,  113 B. In this position, cementing operations may be commenced. 
     During cementing of the casing liner  200  (FIG. 1) to the borehole, cement is pumped downward through the casing liner, out of the axial bore of housing  101 , and upward into the annulus between the borehole and the casing liner. To pass the closed flappers  110 A,  110 B of flapper valve assemblies  114 A,  114 B, the hydrostatic pressure of the cement is increased to overcome the resistance of the springs  111 A,  111 B of the flappers. Once the predetermined quantity of cement is deployed and the hydrostatic pressure is reduced, the springs  111 A,  111 B of the flapper valve assemblies  114 A,  114 B force the flappers  110 A,  110 B upwards to engage the frustoconical valve bodies  113 A,  113 B. This once again obstructs the flow path through the housing  101  and prevents the cement from traveling back into the casing liner  200  (FIG.  1 ). 
     Finally, once cementing operations are completed, the components of float collar assembly  100 A are drilled out to provide an open flow path to the bottom of the borehole. 
     With reference to FIG. 5, a second embodiment of a float collar assembly  100 B in accordance with the present invention comprises a housing  400 , two flapper valve assemblies, and a valve-actuating sleeve  410 . Each flapper valve assembly comprises a flapper  407 A,  407 B, a flapper recess  408 A,  408 B, a pin and spring  409 A,  409 B, and a frustoconical valve body  406 A,  406 B. The actuating sleeve  410  comprises a drop ball seat  415  being integral with the inner surface of the actuating sleeve and having an axial bore therethrough for receiving a drop ball  420  (FIGS.  6 A- 6 C). The diameter of the drop ball  420  (FIGS. 6A-6C) is less than or equal to diameter of the actuating sleeve  410 , but greater than diameter of the axial bore of the drop ball seat  415 . Additionally, the actuating sleeve  420  comprises a shoulder  418  protruding radially outward for engaging with a groove  401  formed in the housing  400  and protruding radially inward. The shoulder  418  is formed near the upper end of the actuating sleeve  420 . 
     With reference to FIGS. 6A-6C, in operation, the second embodiment of a float collar apparatus of the present invention is installed within the lower end of a casing liner  200  (FIG. 1) with the actuating sleeve  410  holding the flappers  407 A,  407 B of the flapper valve assemblies in an open position against the tension of the flapper springs  409 A,  409 B. The actuating sleeve  410  is restrained from axial displacement by the protruding shoulder  418  of the actuating sleeve and the groove  401  of the housing  400 . This creates an open flow path through which drilling fluid can pass unobstructed through the axial bore of housing  400 . 
     With reference to FIG. 6A, once the casing liner  200  (FIG. 1) is lowered to total depth, a drop ball  420  is dropped down the casing liner, through the upper end of the housing  400 , and into the drop ball seat  415 . The drop ball  420  seals with the drop ball seat  415  thereby obstructing the flow path of drilling fluid through the casing liner  200  (FIG.  1 ). 
     Next, with reference to FIG. 6B, drilling fluid pressure is increased above the drop ball  420  and the drop ball seat  415  to a predetermined level such that the shoulder  418  (FIG. 6A) of the actuating sleeve  410  is sheared by the groove  401  of the housing  400 . With the shoulder  418  (FIG. 6A) sheared, the actuating sleeve  410  is free to displace axially downward out of the housing  400  to the bottom of the borehole. 
     With reference to FIG. 6C, once the actuating sleeve  410  is displaced from the housing  400 , the flappers  407 A,  407 B of the flapper valve assemblies are forced by the springs  409 A,  409 B to rotate into engagement with the frustoconical valve bodies  406 A,  406 B. In this position, cementing operations may be commenced following the same steps as in the first embodiment. 
     With reference to FIG. 7A, an alternative valve-actuating sleeve  410 B of the second embodiment of the float collar assembly comprises a drop ball seat  415 B integral with the actuating sleeve and a shearing sleeve  455  attached to the upper end of the actuating sleeve  410 B. The shearing sleeve  455  is fabricated from a lightweight metal, preferably aluminum. The shearing sleeve  455  is preferably in threaded connection with upper end of the actuating sleeve  410 B, but it is intended that any secure connecting means known in the art may be employed. 
     Still with reference to FIG. 7A, the shearing sleeve  455  comprises a shoulder  456  protruding radially outward for engaging with the groove  401  in the housing  400  of the float collar assembly  100 B (FIG.  5 ). The shoulder  456 B is formed near the upper end of the shearing sleeve  455 . A shearing recess  457  is formed between the upper end and lower end of the shearing sleeve  455 . The shearing recess  457  is formed such that the thickness of the wall of the shearing sleeve  455  is smallest at the recess. 
     With reference to FIG. 7B, to displace the actuating sleeve  410 B from the housing  400  (FIG.  5 ), a drop ball  420 B is landed in the drop ball seat  415 B. The drop ball  420 B seals with the drop ball seat  415 B thereby obstructing the flow path of drilling fluid through the casing liner  200  (FIG.  1 ). Next, drilling fluid pressure is increased above the drop ball  420 B and the drop ball seat  415 B to a predetermined level such that the shearing sleeve  455  is sheared at the shearing recess  457 . With the shearing sleeve  455  sheared, the actuating sleeve  410 B is free to displace axially downward out of the housing  400  (FIG. 5) to the bottom of the borehole. 
     Each of the embodiments of the present invention comprises components fabricated from materials such that the float collar assembly can endure high stresses typical of a running in and cementing operation, but can also be drilled out of the casing liner in a shorter period of time than that of prior art float collars. Accordingly, the flapper valve assemblies and the actuating sleeve and seat of each embodiment are fabricated from a hardened plastic material. However, the housing is fabricated from a lightweight metal or other hardened material having bearing and wear characteristics that are sufficient to endure high stresses involved in running in and cementing operations. 
     In a particular embodiment of the present invention, the hardened plastic material is a modified nylon blend material, such as Vekton 6XAU, manufactured by Ensinger, Inc. Vektron 6XAU is a cast type 6 nylon having enhanced heat-resistant, weather-resistant, and bearing properties. 
     In another embodiment of the present invention, the valve-actuating sleeve is fabricated from a phenolic-nylon laminate. With respect to FIGS. 8A and 8B, the valve-actuating sleeve  500  has an outer phenolic layer  501  and an inner nylon layer  502 . The phenolic layer  501  provides enhanced tensile strength properties, while the nylon layer  502  reinforces the phenolic layer to enable the actuating sleeve  500  to resist high impact loads. Furthermore, in accordance with this embodiment of the present invention, the flapper valve assemblies are fabricated from a phenolic material. 
     While preferred embodiments of the present invention comprise components which are fabricated from a nylon material, a phenolic material, or a phenolic-nylon laminate, it is intended that these components may be fabricated from any plastic-material having thermal-resistant, bearing, and fatigue characteristics that are sufficient to endure high stresses involved in running in and cementing operations, but that will yield at a lower stress than metal components during drill out operations. 
     While prior art full metal float collars typically require about six hours to drill out, the non-metal components of the float collar of the present invention are more yielding to drill out operations and are expected to reduce drill out time substantially. However, the float collar assembly of the present invention can still withstand a maximum stress of approximately 600 psi. 
     As used in the appended claims, the term “connecting means” is intended to cover a shear pin, shearing shoulder, or shearing sleeve as described herein, and all equivalents of such structures. 
     Furthermore, as used in the appended claims, the term “hardened material” is intended to mean lightweight metal, such as aluminum, or a hardened plastic material having bearing and wear characteristics that are sufficient to endure high stresses involved in running in and cementing operations, such as phenolic, and all equivalents of such structures. 
     Still furthermore, as used in the appended claims, the term “hardened plastic material” is intended to mean nylon material, phenolic material, phenolic-nylon laminate, or another plastic material having thermal-resistant, bearing, and fatigue characteristics that are sufficient to endure high stresses involved in running in and cementing operations, but that will yield at a lower stress than metal components during drill out operations, and all equivalents of such structures.