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[0001]    This invention relates to a tool used in wells extending into the earth and, more particularly, to a tool for isolating one section of a pipe string from another section. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are a number of situations, in the completion of oil and gas wells, where it is desirable to isolate one section of a subterranean well from another. For example, in U.S. Pat. No. 5,924,696, there is disclosed an isolation tool used alone or in combination with a packer to isolate a lower section of a production string from an upper section. This tool incorporates a pair of oppositely facing frangible or rupturable discs or half domes which isolate the well below the discs from pressure operations above the discs and which isolate the tubing string from well bore pressure. When it is desired to provide communication across the tool, the upper disc is ruptured by dropping a go-devil into the well from the surface or well head which falls into the well and, upon impact, fractures the upwardly convex ceramic disc. The momentum of the go-devil normally also ruptures the lower disc but the lower disc may be broken by application of pressure from above, after the upper disc is broken, because the lower disc is concave upwardly and thereby relatively weak against applied pressure from above. 
         [0003]    An important development in natural gas production in recent decades has been the drilling of horizontal sections through zones that have previously been considered uneconomically tight or which are shales. By fracing the horizontal sections of the well, considerable production is obtained from zones which were previously uneconomical. For some years, the fastest growing segment of gas production in the United States has been from shales or very silty zones that previously have not been considered economic. The current areas of increasing activity include the Barnett Shale, the Haynesville Shale, the Fayetteville Shale, and the Marcellus Shale in the United States, the Horn River Basin of Canada and other shale or shaley formations in North America and Europe. 
         [0004]    It is no exaggeration to say that the future of natural gas production in the continental United States is from these heretofore uneconomically tight gas bearing formations. In addition, there are many areas of the world where oil and gas is produced and costs are, from the perspective of a United States operator, exorbitantly high. These areas currently include offshore Africa, the Middle East, the North Sea and deep water parts of the Gulf of Mexico. Accordingly, a development that allows well completions at overall lower costs is important in many areas of the world and in many different situations. 
         [0005]    Disclosures of interest relative to this invention are found in U.S. Pat. Nos. 7,044,230; 7,210,533 and 7,350,582 and U.S. Printed Patent Applications S.N. 20070074873; 20080271898 and 20090056955. 
       SUMMARY OF THE INVENTION 
       [0006]    The device disclosed in U.S. Pat. No. 5,924,696 can be used in a horizontal section of a well to isolate the well below the tool from pressure operations above the tool. However, the upper disc has to be broken or weakened in a mechanical fashion requiring a bit trip, typically a coiled tubing trip in modern high tech wells or a bit trip with a workover rig in more traditional environments, to fracture the upper disc because a go-devil dropped through the vertical section of the well does not have sufficient momentum to reach and then fracture the upper disc. Theoretically, sufficient pressure could be applied from above to break the upper disc from the concave side but this pressure is commonly so high that it would damage or destroy other components of the production string. It has been realized that it would be desirable to provide an isolation tool which can be used in a horizontal section of a well without requiring a bit trip. 
         [0007]    As disclosed herein, a pressure differential that is uniform across the pressure disc is created by manipulating pressure at the surface or through the well head to fracture a first of the discs. The other disc may be ruptured using pressure in the well. The exact sequence of breaking the discs may depend on the particular design employed and whether the isolation tool is located above or below a packer or other sealing element isolating the production string, typically from a surrounding pipe string 
         [0008]    Several embodiments of an isolation tool are disclosed that may be used in wells to temporarily isolate a section of the well below the tool from a section above the tool. These embodiments use a pressure differential to fracture a first of the discs. In one embodiment, a capillary tube is provided from above the upper disc to a location between the discs. In a second embodiment, a check valve admits pressurized well fluid between the discs so that one of the discs may be broken by reducing the pressure on one side of the isolation tool. In a third embodiment, an unvalved opening admits pressurized well fluid between the discs so that one of the discs may be broken by reducing the pressure on one side of the isolation tool. In a fourth embodiment, a movable member is displaced by pressure supplied from above to break a first of the discs. 
         [0009]    It is an object of this invention to provide an improved down hole well tool to isolate one section of a well from another. 
         [0010]    A more specific object of this invention is to provide an improved isolation sub that can be manipulated by a pressure differential to place isolated sections of a well into communication. 
         [0011]    These and other objects and advantages of this invention will become more apparent as this description proceeds, reference being made to the accompanying drawings and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a cross-sectional view of one embodiment of an isolation tool that incorporates a pair of oppositely facing pressure discs; 
           [0013]      FIG. 2  is an exploded view of a component of the device of  FIG. 1 ; 
           [0014]      FIG. 3  is a schematic view of a well in which the isolation tool of  FIG. 1  is employed; 
           [0015]      FIG. 4  is a cross-sectional view of another embodiment of an isolation tool that incorporates a pair of oppositely facing pressure discs; 
           [0016]      FIG. 5  is an enlarged view of a valve assembly used in the embodiment of  FIG. 4 ; 
           [0017]      FIG. 6  is a view similar to  FIG. 2 , illustrating operation of the embodiment of  FIGS. 4 and 5 ; 
           [0018]      FIG. 7  is a partial view of another embodiment of this invention, based on the embodiment of  FIG. 4 ; 
           [0019]      FIG. 8  is a cross-sectional view of another embodiment of an isolation tool that incorporates a pair of oppositely facing pressure discs, illustrating the tool in a position where upper and lower sections of the well are isolated; 
           [0020]      FIG. 9  is a cross-sectional view of the embodiment of  FIG. 5  illustrating the tool in the process of breaking one of the pressure discs; 
           [0021]      FIG. 10  is an isometric view of a modified pressure dome; and 
           [0022]      FIG. 11  is a view of the pressure dome of  FIG. 10  in an isolation tool. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Referring to  FIGS. 1-2 , there is illustrated an isolation tool or sub  10  comprising a housing  12  having a passage  14  therethrough, upper and lower rupturable pressure discs  16 ,  18  and a capillary tube  20  opening into a chamber  22  between the discs  16 ,  18 . 
         [0024]    The housing  12  may comprise a lower end, pin body or pin  24 , a central section  26 , an upper end or box body  28  and suitable sealing elements or O-rings  30 ,  32  captivating the discs  16 ,  18  in a fluid tight manner. Except for the capillary tube  20 , those skilled in the art will recognize the isolation sub  10 , as heretofore described, as being typical of isolation subs sold by Magnum International, Inc. of Corpus Christi, Tex. and as also described in U.S. Pat. No. 5,924,696. 
         [0025]    The capillary tube  20  may be external to the housing  12 , or an internal passage may be provided, and may terminate in an extension of the central section  26  or in the upper section  28 . One problem that is occasionally encountered is sufficient debris above the upper disc  16  which might seal off pressure from reaching the capillary tube  20 . To overcome this problem, the capillary tube  20  may be of greater length as by providing one or more pipe sections  34  of any suitable length connected to a collar or other sub  36  thereby elongating the housing  12 . This will accommodate debris, such as sand or the like, from bridging off access to the top of the capillary tube  20 . 
         [0026]    The discs  16 ,  18  may be of any suitable type having the capability of being stronger in one direction than in an opposite direction. Conveniently, the discs  16 ,  18  may be curved or generally hemispherical domes made of any suitable material, such as ceramic, porcelain, glass and the like. Suitable ceramic materials, such as alumina, zirconia and carbides are currently commercially available from Coors Tek of Golden, Colo. These materials are frangible and rupture in response to either a sharp blow or in response to a pressure differential where high pressure is applied to the concave side of the discs  16 ,  18 . Because of their curved or hemispherical shape, half domes may be a preferred selection because of their considerable ability to resist pressure from the convex side, their much lower ability to resist pressure from the concave side, cost, reliability and frangibility. Ceramic discs of this type are available in a variety of strengths but a typical disc may have the capability of withstanding 25,000 psi applied on the convex side but only 1500 psi applied on the concave side. In a typical situation, the discs  16 ,  18  may be 10-20 times stronger against pressure applied to the convex side than to the concave side. Any pressure disc which has greater strength in one direction than in the opposite may be used, another example of which are metal Scored Rupture Disc Assemblies available from Fike Corporation of Blue Springs, Mo. or BS&amp;B of Tulsa, Okla. The Fike discs that are stronger in one direction than the other are also concave on the weak side and convex on the other which is a convenient technique for making the discs stronger in one direction than in an opposite direction and thus responsive to different sized pressure differentials. 
         [0027]    The capillary tube  20  includes a tube  38  of any suitable outside and inside diameter so long as it transmits pressure, either higher or lower than hydrostatic pressure in the well applied from above the tool  10 . The tube  20  may be connected to the central section  26  in a recess  40  by a nipple  42  threaded, pressed or otherwise connected to the central section  26 . The nipple  42  communicates with a passage  44  opening into the chamber  22  so any pressure, higher or lower than hydrostatic pressure, applied above the tool  10  is delivered between the discs  16 ,  18 . A connector  46  may be threaded into the nipple  42  as driven by a wrench (not shown) acting on a polygonal nut  48 . A similar or dissimilar fitting  50  may connect an upper end of the tube  38  to the collar  36 . 
         [0028]    Referring to  FIG. 3 , a typical example of using the isolation tool  10  is illustrated. The isolation tool  10  may comprise part of a horizontal or inclined section of a production string  52  inside a casing string  54  which intersects a productive zone where one or more pipe joints  56  may be disposed below the tool  10  and a series of pipe joints  58  may be disposed above the tool  10  leading to the surface or well head so formation fluids may be produced. A typical use of the isolation tool  10  is to isolate the productive zone below a packer  60  from pressure operations above the tool  10  which operations typically set the packer  60 . Another typical use of the isolation tool  10  is in setting a liner during drilling of a deep well. 
         [0029]    At the outset and throughout the packer setting operation, there is hydrostatic pressure inside the production string  52  and in the annulus between the production string  52  and the casing string  54 , meaning there is hydrostatic pressure above the upper disc  16 , in the chamber  22  and below the lower disc  18 , so there is no pressure differential operating on the discs  16 ,  18  which would tend to break them. The packer  60  is set by applying pressure downwardly through the production string  52 . Any pressure applied from above acts on both sides of the upper disc  16  so the upper disc  16  sees no pressure differential and there is no tendency of the upper disc  16  to fail. So long as the packer  60  is set by a pressure that is less than the sum of hydrostatic pressure at the tool  10  and the strength of the disc  18  against pressure applied on the concave side, the packer  60  may be manipulated without fracturing the lower disc  18 . 
         [0030]    After the packer  60  is set, pressure is applied from above and transmitted through the capillary tube  20  to a location between the discs  16 ,  18 . This applied pressure is greater than the hydrostatic pressure in the well and creates a pressure differential which is uniform over the area of the disc  18  and which exceeds the ability of the concave side of the lower disc  18  to withstand it. The lower disc  18  then shatters or ruptures allowing well pressure to enter the chamber  22 . When pressure in the production string  52  above the tool  10  is lowered, as by stopping the pumps which have created the pressure to set the packer  60 , by swabbing the production string  52 , gas lifting the production string  52  or simply opening the production string  52  to the atmosphere at the surface or well head, well pressure acting on the concave side of the upper disc  16  exceeds its ability to withstand pressure in this direction whereupon the upper disc  16  fails thereby placing the production string  52 , above and below the tool  10 , in communication and allowing the well to produce. Thus, the tool  10  allows breaking of the discs  16 ,  18  to place the heretofore isolated parts of the well in communication by the application of pressure from above. In this situation, the pressure that breaks the lower disc  18  is applied from above and produces a pressure at the tool  10  that is greater than hydrostatic pressure but far less than what would rupture the disc  16  if applied from above. 
         [0031]    Many, if not most, hydraulically set packers require more pressure above hydrostatic than the concave side of the lower disc  18  can withstand. To overcome this problem, an inline pressure disc  62  may be provided in the capillary tube  20  as shown best in  FIG. 3 . In some embodiments, the pressure disc  62  may be located between the nipple  42  and the passage  44 , may be located inside the nipple  42 , inside the fitting  50  or any other suitable location. The pressure disc  62  may be of any suitable type to provide a sufficient resistance to allow the packer  60  to be hydraulically set without rupturing the lower disc  18 . In some embodiments, the pressure disc  62  is commercially available from Fike Corporation of Blue Springs, Mo. and known as Scored FSR Rupture Disc Assembly. In a typical situation, the packer  60  may require an applied pressure of 3500 psi above hydrostatic to set. In such situations, the pressure disc  62  may be selected to rupture at a substantially greater pressure, e.g. 4500 psi. Thus, the packer  60  would be set and then additional pressure would be applied to rupture the disc  62  which would place sufficient pressure in the chamber  22  to fracture the lower disc  18 . The upper disc  16  would not rupture immediately because there is initially no pressure differential across the upper disc  16  because the pressure applied from the surface is on both sides of the upper disc  16 . After the lower disc  18  fails, pump pressure applied from the surface is reduced whereupon formation pressure applied from below produces a pressure differential sufficient to rupture the upper disc  16 . 
         [0032]    In some embodiments, a check valve (not shown) may be provided in the fitting  50  to allow flow inside the tubing string  58  to enter the chamber  22  but prevent flow out of the chamber  22 . 
         [0033]    It will be seen that the tool  10  is designed to cause one of the pressure discs  16 ,  18  to fail by creation of a pressure differential that is substantially below the differential pressure which would cause failure if applied to the strong or convex side of the pressure discs  16 ,  18 . 
         [0034]    Referring to  FIG. 4 , there is illustrated another isolation tool  70  providing a passage  72  therethrough and comprising, as major components, a housing  74 , first and second pressure discs  76 , and a valve assembly  80  allowing hydrostatic pressure from outside the tool  70  to enter a chamber  82  between the pressure discs  76 ,  78 . 
         [0035]    The housing  74  may comprise a lower end or pin body  84 , a central section or collar  86  providing a passage  88  into the chamber  82 , an upper end or box body  90  and suitable sealing elements or O-rings  92 ,  94  captivating the discs  76 ,  78  in a fluid tight manner. The pressure discs  76 ,  78  may be of the same type and style as the pressure discs  16 ,  18  and are capable of resisting a greater pressure from one direction than the other. Except for the valve assembly  80 , those skilled in the art will recognize the isolation sub  70 , as heretofore described, as being typical of isolation subs sold by Magnum International, Inc. of Corpus Christi, Tex. and as also being described in U.S. Pat. No. 5,924,696. 
         [0036]    The valve assembly  80  comprises a check valve which allows flow into the chamber  82  so hydrostatic pressure is delivered between the discs  76 ,  78  during normal operations, such as when the tool  70  is being run into a well. The valve assembly  80  may comprise a spring  96  biasing a ball check  98  against a valve seat  100 . It will be seen that the check valve  80  allows the maximum hydrostatic pressure to which the tool  70  is subjected to appear in the chamber  82 . Under normal conditions, there is no tendency for the pressure in the chamber  82  to rupture the discs  76 ,  78  because the same pressure exists on the inside and outside of the tool  70 . 
         [0037]    Referring to  FIG. 6 , the isolation tool  70  is illustrated in a production string  102  inside a casing string  104 . A pressure actuated packer  106  may be above the isolation tool  70 . The production string  102  may extend past the tool  70  toward a hydrocarbon formation. Initially, the isolation tool  70  pressure separates the production string  102  into two segments. Because of the inherent strength of the convex side of the illustrated disc  76 , the applied pressure may be sufficiently high to conduct any desired pressure operation. After the packer  102  is set or when it is desired to place the well below the tool  70  in communication with the production string  102  above the tool  70 , steps are conducted to reduce pressure above the upper disc  76 . This may be done in any suitable manner, as by opening the production string  102  at the surface or through the well head, swabbing the production string  102 , gas lifting the production string  102  or the like. When the pressure above the upper disc  76  declines sufficiently, a pressure differential is created across the upper disc  76  which is sufficient to rupture the upper disc  76 . This pressure differential is much smaller than a pressure differential caused by the application of positive pressure to the convex side of the upper disc  76  that is sufficient to rupture it. For example, the convex side of the disc  76  may be rated to withstand a pressure differential of 25,000 psi but the embodiment of  FIG. 4  acts to rupture the upper disc  76  upon creating a much smaller pressure differential applied to the concave side of the disc  76 . 
         [0038]    After the upper disc  76  ruptures, pressure may be applied at the surface through the production string  102  by a suitable pump (not shown) to create a pressure differential across the lower disc sufficient to rupture it. In this manner, the heretofore pressure separated sections of the well are now in communication. 
         [0039]    Referring to  FIG. 7 , there is illustrated another isolation tool  110  which may be identical to the tool  70  except that the check valve assembly  80  has been eliminated. Thus, the tool  110  may include a collar  112  having one or more continuously open or unvalved passages  114  therein communicating between the pressure discs. By continuously open, it is meant that the passage  114  is open when the tool  110  is in the well. Surprisingly, the tool  110  works in the same manner as the tool  70  because the passage  114  allows hydrostatic pressure to build up between the discs. When liquids above the upper disc are removed, a pressure differential is created across the upper disc in its weak direction thereby rupturing the upper disc. The lower disc is broken in the same manner as the lower disc  78  which may be by pumping into the tool  110 . Besides the advantage of simplicity, the tool  110  also has an advantage when it becomes necessary or desirable to remove the production string and packer from the well without setting the packer. In the embodiment of  FIGS. 4-5 , pulling the tool  70  from the well will reduce pressure above the upper disc  76  and below the lower disc  78  so the trapped pressure in the chamber  82  will likely cause one of the discs  76 ,  78  to fail. By removing the check valve assembly  80 , the isolation tool  110  may be pulled from the well without rupturing either of the pressure discs because hydrostatic pressure will bleed off from between the discs at the same rate as it falls above the upper disc and below the lower disc. By eliminating the check valve assembly  80 , there is created an isolation tool which will not rupture when the tool is pulled from the well. 
         [0040]    Referring to  FIGS. 8-9 , there is illustrated another isolation tool  120  providing a passage  122  therethrough and comprising, as major components, a housing  124 , first and second frangible pressure discs  126 ,  128  and an assembly  130  responsive to pressure inside the tool  120  to rupture the discs  126 ,  128 . 
         [0041]    The housing  124  may comprise a lower end or pin body  132 , a central section or collar  134 , a section  136  that cooperates with the assembly  130 , an upper end or box body  138 , and suitable sealing elements or O-rings  140 ,  142  captivating the discs  126 ,  128  in a fluid tight manner. Another set of seals or O-rings  144  seal between the section  136  and the box body  138 . 
         [0042]    The section  136  includes a wall  146  of reduced thickness providing a recess  148  open to the exterior of the tool  120  through one or more passages  150 . The assembly  130  may include a sleeve  152  having an annular rim  154  comprising a pressure reaction surface. An O-ring or other seal  156  may seal between the rim  154  and the inside of the wall  146  to provide a piston operable by a pressure differential between hydrostatic pressure in the well acting through the passage  150  against the underside  158  of the rim  154  and pressure applied from above acting on the top  160  of the rim  154 . The sleeve  152  may normally be kept in place by a shear pin  162  or other similar device. 
         [0043]    It will be seen that a pressure applied from above through the inside of the tool  120  passes through an opening  164  in the box body  138  and acts on the top  160  of the rim  154 . When the downward force applied in this manner sufficiently exceeds the upward force on the rim  134  by hydrostatic pressure outside the tool  120 , the shear pin  162  fails and the sleeve  152  moves from an upper position shown in  FIG. 8  to a lower position shown in  FIG. 9 . 
         [0044]    The bottom of the sleeve  152  may be equipped with a suitable aid to fracture the upper disc  126 . This may be a pointed element  166  attached to the inside of the sleeve  152  in any suitable manner, as by a lattice work frame  168 . 
         [0045]    As in the previously described embodiments, the isolation tool  120  may be used in any situation where it is desired to pressure separate one section of a hydrocarbon well from another. Assuming the tool  120  is run in a production string analogous to those shown in  FIGS. 2 and 6 , pressure applied from above is sufficient to hydraulically set a packer (not shown) but is not sufficient to shear the pin  162 . After the packer (not shown) is set, additional pressure is applied from above which is sufficient to shear the pin  162  but is not sufficient to fracture the convex side of the disc  126 . When the pin  162  shears, the sleeve  152  moves downwardly with sufficient force that the point  166  impacts the frangible disc  126  thereby rupturing it. Pressure inside the tool  120  is sufficient to rupture the much weaker lower disc  128  because the pressure differential is applied to the concave side of the disc  128 . Thus, in common with the tools  10 ,  70 , the isolation tool  120  opens communication between the previously isolated parts of a well upon the application of pressure from above that is less than the rated capacity of the convex side of the upper disc  126 . 
         [0046]    Referring to  FIGS. 10-11 , an improved pressure disk  170  is illustrated having a generally hemispherical central section  172  providing a circular edge  174 , a convex outer surface  176 , a concave inner surface  178  and a cylindrical skirt  180  extending substantially from the circular edge  174  below the curved portion of the disk  170 . The cylindrical skirt  180  includes an inner cylindrical wall  182  and an outer cylindrical wall  184  providing an extended sealing area as shown in  FIG. 11  where multiple sealing elements or O-rings  186 ,  188  seal between the disk  170  and a housing  190  which may be part of an isolation tool  192  or other tool where a frangible pressure disk is necessary or desirable. 
         [0047]    The advantage of the elongate cylindrical skirt  180  is it provides sufficient area for multiple sealing elements, such as a pair of O-rings or other seals or one or more seals with a backup seal or device. It is much simpler to seal against the outer cylindrical wall  184  than against a curved portion of the hemi-spherical central section  172 . In fact, seals heretofore used with hemispherical pressure disks of the type disclosed herein were crushed to accommodate and seal against the arcuate side of the pressure disk. Sealing against the cylindrical surface  182  is much simpler, more reliable, more reproducible and more efficient. Thus, the skirt  180  may be of any suitable length sufficient to provide a cylindrical surface of sufficient length to receive at least one seal member on the O.D. and, preferably, two seal members. Thus, in a typical situation in disks  170  of 2″ diameter and greater the skirt  180  may be at least 1″ long. 
         [0048]    The disk  170  may be made of any frangible material, such as ceramic, porcelain or glass, i.e. from the same materials as the pressure disks previously described. 
         [0049]    It will be apparent that the outer cylindrical wall  184  may be manufactured in a variety of techniques. One simple technique is to grind the outer diameter of a hemispherical disk to provide the cylindrical wall  184 . A preferred technique may be to manufacture the disk  170  with an elongate cylindrical skirt  180  as illustrated in  FIGS. 10-11  and then grind the outer diameter to a smoothness compatible with O-ring type seals. This smoothness, known to machinists as a seal finish or O-ring seal finish is known more technically as 63-32 on a scale known as RMS or Root Mean Square. In this system, and simplified for purposes of illustration, the number is a measure, in microns, of the difference between the heights of small protrusions and the depths of small depressions in the surface. The smaller the number, the smoother the surface. 
         [0050]    Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

Summary:
A down hole pressure isolation tool is placed in a pipe string and includes a pair of pressure discs having one side that is highly resistant to applied pressure and one side that ruptures when much lower pressures are applied to it. The weak sides of the pressure discs face each other. Rather than rupturing the discs by dropping a go-devil into the well, a first of the discs is ruptured or broken by the application of fluid pressure from the well head or surface. Formation pressure is then used, in different ways according to the different embodiments, to rupture the remaining disc.