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TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to the drilling of subterranean wells and, more particularly to filling casing and casing string with drilling fluid and providing for the flow back of said fluids. 
       BACKGROUND OF THE INVENTION 
       [0002]    The process of drilling subterranean wells to recover oil and gas from reservoirs, typically consists of boring a hole in the earth down to the petroleum accumulation and installing pipe from the reservoir to the surface. Casing is generally a protective pipe liner within the wellbore that may be cemented in place to insure a pressure-tight connection to the oil and gas reservoir. The casing is typically run in single or multiple joints at a time as it is lowered into the wellbore. On occasion, the casing becomes stuck and is unable to be lowered into the wellbore. When this occurs, load must be added to the casing string to force the casing into the wellbore, or drilling fluid must be circulated down the inside diameter of the casing and out of the casing into the annulus in order to free the casing from the wellbore. To accomplish this, it has traditionally been the case that special rigging be installed to add axial load to the casing string or to facilitate circulating the drilling fluid. 
         [0003]    When running casing, drilling fluid is added to the casing section(s) as it is run into the wellbore. This procedure is necessary to prevent the casing from collapsing due to high pressures within the wellbore. The drilling fluid acts as a lubricant which facilitates lowering the casing within the wellbore. As joints of casing are added to the string, drilling fluid is displaced from the wellbore. Typically, hose assemblies, housings coupled to the uppermost portion of the casing, and/or tools suspended from the drill hook for filling the casing were utilized. Others employed sealing elements which would seat against the inside of the casing, followed by a mechanical setdown force which opened ports to allow for circulation. Seals between a mandrel and a movable sleeve were also needed to retain a sealed connection to allow circulation. Filling in these devices was accomplished by displacement of a valve member past a lateral port to expose the lateral port to allow the casing to fill. Frequently, excessive erosion occurred at the valve member used for filling the casing, undermining its reliability. Additionally, some designs required at least two separate valves, one for filling the casing and the other for circulating the fluid. Typically, the circulating ports had to be mechanically exposed using setdown weight or other manual intervention. In addition to erosion, additional valve components were required for operation. 
         [0004]    Circulating of the fluid is some times necessary if resistance is experienced as the casing is lowered into the wellbore. In order to circulate the drilling fluid, the top of the casing must be sealed so that the casing may be pressurized with drilling fluid. Since the casing is under pressure the integrity of the seal is critical to safe operation, and to minimize the loss of the expensive drilling fluid. Once the casing reaches the bottom, circulating of the drilling fluid is again necessary to test the surface piping system, to condition the drilling fluid in the hole, and to flush out wall cake and cuttings from the hole. Circulating is continued until at least an amount of drilling fluid equal to the volume of the inside diameter of the casing has been displaced from the casing and wellbore. After the drilling fluid has been adequately circulated, the casing may be cemented in place. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    For a further understanding of the nature and objects of the instant disclosure, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers. 
           [0006]      FIG. 1  illustrates a pictorial view of a self actuating casing tool in accordance with the present disclosure; 
           [0007]      FIG. 2  illustrates an exploded view of a pressure actuated piston type casing fill-up valve in accordance with the present disclosure; and 
           [0008]      FIG. 3  illustrates a cross sectional view of a pressure actuated piston type casing fill-up valve in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0009]    The present disclosure provides a device that simplifies the construction of an apparatus utilized for filling and circulating fluid within casing and/or a wellbore. The disclosed device provides, among other things, an automatic piston type pressure actuated valve which allows fluid, such as drilling fluid, to pass through the valve and into the casing without intervention. As described hereinbelow, the piston allows for activation without manual assistance or other manipulation of the valve. Further as the fluid flow is discontinued, the valve closes due to the substantial lack of pressure and retains the fluid in the casing. It should be appreciated that the fluid may exit at the bottom of the casing string and move into the wellbore. 
         [0010]    Referring now to  FIG. 1 , an embodiment of the self actuating casing tool  2  is illustrated. Preferably, the self actuating casing tool  2  comprises a hook  4  which may adapt to conventional type Kelly systems. It should be further understood that hook  4  is for a connection to a conventional rig drive. However, connections directly to top drives as well as a variety of other connections are envisioned and as such should not be viewed as a limitation thereof. Further, a connection  6  is preferably provided for connection to a hose to provide drilling fluid or mud for the filling of the casing joints and/or casing string. It should be understood that connection  6  is for example only and that a variety of connections, for fluid, may be utilized. Preferably, the casing tool  2  will have an additional length section  8  which allows for length adjustment and/or to provide travel limitation, when the tool is utilized in conjunction with a conventional push plate  10 . It should be understood that push plate  10  may also serve to limit travel of the tool  2  and is preferably adjustable along the length of section  8 . 
         [0011]    Below push plate  10 , there are preferably one or more subs  12 . Sub or subs  12  are preferably used to adust the correct length of tool  2  to provide for the desired operational use of tool  2 . The sub or subs  12  preferably comprise threaded ends for connection purposes. It should be understood that the connection, of the sub or subs  12  can be a variety of connection methods such as but not limited to left hand threads to deter disconnection, of the sub or subs  12 , during tool operation and thus the specific configuration of the connection should not be viewed as a limitation herein. In at least one embodiment, the subs  12  are designed so as to allow multiple re-cuts on the connection threads. It should be appreciated that the connection threads of the sub or subs  12  can be worn or damaged after several uses due to environmental conditions and/or corrosion/erosion. It should be further appreciated that the multiple re-cuts allow for quick and/or easy repair of the subs  12 . 
         [0012]    Preferably, between the pressure actuated piston type casing fill-up valve  16  and the sub or subs  12  are one or more sealing elements  14 . It should be understood that the exact configuration and/or location of the sealing members  14  may vary regarding the preferred/required distance in order to achieve the proper placement of the pressure actuated piston type casing fill-up valve  16  and the sealing elements  14 . It should be further understood that elements  14  may be conventional sealing elements well known in the art and utilized to seal against the internal casing wall to allow fluid circulation. 
         [0013]    In at least one embodiment and as described hereinbelow, the pressure actuated piston type casing fill-up valve  16  is manufactured of materials or coated with materials or incorporates specifically treated materials which help to eliminate and/or reduce wear in the pressure actuated piston type casing fill-up valve  16 . 
         [0014]      FIG. 2  illustrates an exploded view of a pressure actuated piston type casing fill-up valve  16 . In one embodiment, pressure actuated piston type casing fill-up valve  16  preferably comprises a lower cylinder  30 . Preferably lower cylinder  30  has at least one port  32  at the lower end. It should be understood that there may be several ports  32  and that the exact position of the ports  32  should not be viewed as a limitation herein. The purpose of the fluid port  32  is to allow the passage of the desired fluid, such as drilling mud, through the casing tool  2  and into the casing and/or casing string. Piston  28  is designed so as to fit into lower cylinder  30 . The cylinder head  26  preferably fits into lower cylinder  30  on top of the piston  28 . Preferably, cylinder head  26  is designed with a retaining lip  27 . Preferably, retaining lip  27  will align with a mating retaining lip  23  in the interior top portion of lower cylinder  30 . It should be appreciated that the configuration of the mating retaining lips  23 ,  27  can be varied. It should be further appreciated that the purpose of the mating retaining lips  23 ,  27  is to retain the cylinder head  26  in position. Thus, piston  28 , when fluid pressure is applied to it, can move away from the cylinder head  26  allowing for the flow of fluid through the piston bore  33 . Upper cylinder portion  18  connects to lower cylinder  30  thus enclosing the piston  28  and cylinder head  26 . It should be appreciated that upon the connection of upper cylinder portion  18  and lower cylinder  30 , the retention of cylinder head  26  is achieved, preferably due to the mating of retaining lips  23 ,  27 . Preferably lower cylinder  30  has a connection  24  and the upper cylinder  18  has a connection end  22 . Although it is preferable that the connections  22 ,  24  be a mating threaded connection, other methods of attachment are foreseeable and should not be viewed as a limitation herein. Further, upper cylinder portion  18  preferably has a conventional pipe thread connection  20  at its upper end. Preferably, the pressure actuated piston type casing fill-up valve  16  and various internal parts are protected against the erosive forces of the drilling fluid as well as other wellbore environmental conditions. In one example, not intended as limiting, the cylinder head  26  is made of a tungsten carbide material and the mating portion of the piston  28  is also of a tungsten carbide material. It has been found that a material with a higher cobalt content provides better erosive resistance. In other examples, also not intended to be limiting, certain pressure actuated piston type casing fill-up valve  16  parts may be gas nitrided for erosive resistance. It should be understood that there may be other methods of protecting the parts against erosion and should not be viewed as a limitation herein. 
         [0015]    Referring now to  FIG. 3  a cross sectional view of an embodiment of a pressure actuated piston type casing fill-up valve  16  is illustrated It can be seen here the functional relationship between the various components described herein above. It should be understood that one or more seals may be employed, as necessary, to prevent leakage. In this embodiment, one or more seals  34  are utilized to seal the connection  22 ,  24  of the upper cylinder  18  and the lower cylinder  30 . Another seal  36  or set of seals are preferably utilized for sealing between the lower cylinder  30  and the piston  28 . 
         [0016]    Still referring to  FIG. 3 , there is illustrated a spring  29 . Preferably spring  29  is designed so as to bias piston  28  in a substantially seal tight relationship with cylinder head  26  when there is no fluid flow through the pressure actuated piston type casing fill-up valve  16 . Thus, the pressure actuated piston type casing fill-up valve  16  remains in a closed position until the force of the fluid, passing through pressure actuated piston type casing fill-up valve  16 , is sufficient to overcome the bias of spring  29 . It should be appreciated that methods, other than a spring, for biasing may be utilized and should not be viewed as a limitation herein. 
         [0017]    In operation, the fluid, such as but not limited to drilling mud enters the pressure actuated piston type casing fill-up valve  16  through upper port  38 . As the fluid contacts the cylinder head  26 , piston  28  will be displaced, by the fluid pressure. Preferably, the displacement, of piston  28  occurs as the fluid passes around the substantially stationary cylinder head  26 . The fluid can then move through the piston bore  33  and into the casing through the lower ports  32 . When the fluid flow is shut off, the spring  29  will move the piston  28  back to its normal or unactuated position and any flow, through the pressure actuated piston type casing fill-up valve  16  is prevented. It should be appreciated that wellbore pressure, below the pressure actuated piston type casing fill-up valve  16 , may aid in moving the piston in contact with the cylinder head  26  thus further preventing any reverse flow through the pressure actuated piston type casing fill-up valve  16 . 
         [0018]    While the present system and method has been disclosed according to the preferred embodiment, those of ordinary skill in the art will understand that other embodiments have also been enabled. Even though the foregoing discussion has focused on particular embodiments, it is understood that other configurations are contemplated. In particular, even though the expressions “in one embodiment” or “in another embodiment” are used herein, these phrases are meant to generally reference embodiment possibilities and are not intended to limit the system or methods disclosed herein to those particular embodiment configurations. These terms may reference the same or different embodiments, and are combinable into aggregate embodiments. The terms “a”, “an” and “the” may also mean “one or more”. 
         [0019]    When a single embodiment is described herein, it will be readily apparent that more than one embodiment may be used in place of a single embodiment. Similarly, where more than one embodiment is described herein, it will be readily apparent that a single embodiment may be substituted for that one device. In light of the wide variety of casing filling activities, the detailed embodiments are intended to be illustrative only and should not be taken as limiting the scope of the instant disclosure. None of the description in this specification should be read as implying that any particular element, step or function is an essential element which must be included in the claim scope. Unless explicitly recited, other aspects of the instant disclosure as described in this specification do not limit the scope of the claims. Because many varying and different embodiments may be made within the scope of the inventive concept(s) herein taught, and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense. Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments described above which are within the full intended scope of the invention as defined in the appended claims.

Summary:
The present disclosure describes a method and apparatus for filling casing and/or a casing string and provides for the flow back of such fluids in a wellbore during casing running operations. The tool comprises a piston valve which is automatically pressure actuated. Thus, the valve will open and close without manual and/or outside mechanical intervention. Further, the design and construction of the piston valve helps to substantially reduce erosive wear to the piston valve and its components.