Abstract:
An embodiment of a ceramic isolation ball is provided to cooperate with a ball seat to isolate a first portion of a well drilled into the earth&#39;s crust from a second portion of the well. Embodiments of the ball of the present invention are comprised of a ceramic material with excellent resistance to deformation when received into a ball seat and subjected to very high pressure differentials tending to force the ball into the ball seat to isolate a portion of a borehole below or beyond the ball and ball seat from a portion of the borehole above or before the ball and ball seat. Embodiments of the ball of the present invention include a hollow interior and a hole that receives a plug to close the hollow interior to prevent fluid intrusion therein. The ball is used to isolate a portion of a well during high-pressure fracturing operations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application depends from and claims priority to U.S. Provisional Patent Application Ser. No. 61/947,271 filed on Mar. 3, 2014, which application is incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an improved ceramic isolation ball for use with a ball seat for isolating a first subsurface geologic zone from a second geologic zone to be subjected to hydraulic fracturing operations to enhance production of hydrocarbons. 
         [0004]    2. Background of the Related Art 
         [0005]    Hydraulic fracturing is the fracturing the rock in a geologic formation using a highly pressurized fracturing liquid. Some hydraulic fractures form naturally in a geologic formation, but an induced hydraulic fracture formed by hydro-fracturing, more commonly known as “fracking,” is a technique by which a volume of water, or some other carrier liquid, mixed with sand and chemicals is injected at a high pressure into a portion of a well to create fractures (typically less than 1 mm wide) through which fluids residing in the formation, such as gas, oil, condensate or other recoverable minerals, may migrate to the wellbore for production to the surface end of the well. Hydraulic pressure is removed from the fractured well and small grains of proppant, for example, sand or aluminum oxide, remain to hold the fractures open once the formation rock is restored to equilibrium. Fracking is commonly used to recover fluids in shale gas, tight gas, tight oil and coal seam gas and hard rock wells. This well stimulation technique is generally only conducted once in the life of the well and greatly enhances fluid removal and well productivity. 
         [0006]    A hydraulic fracture is formed by pumping fracturing fluid into the well at a rate sufficient to increase pressure downhole at a targeted zone (determined by the location of the well casing perforations) to exceed that of the fracture gradient (pressure gradient) of the rock. The fracture gradient is defined as the pressure increase per unit of the depth due to its density and it is usually measured in pounds per square inch per foot or bars per meter. The rock cracks and the fracture fluid continues further into the rock, extending the crack still further, and so on. Fractures are localized because pressure drop off with frictional loss attributed to the distance from the well. Operators typically try to maintain “fracture width,” or slow its decline, following treatment by introducing into the injected fluid a proppant—a material such as grains of sand, ceramic beads or other particulates that prevent the fractures from closing when the injection is stopped and the pressure of the fluid is removed. The propped fracture is permeable enough to allow the flow of formation fluids to the well. Formation fluids include gas, oil, salt water and fluids introduced to the formation during completion of the well during fracturing. 
         [0007]    The location of one or more fractures along the length of the borehole is strictly controlled by various methods that create or seal off holes in the side of the well. A well may be fracked in stages by setting a ball seat within the well casing and below or beyond the targeted geologic formation to isolate one or more lower zones that are open to the well from the anticipated fracking pressure. A ball of a predetermined diameter is introduced into the well at the surface and pumped downhole. When the ball reaches the ball seat, the ball seats in the ball seat to form a pressure seal and to isolates the geologic formation zones below or beyond the ball seat from the anticipated hydraulic fracturing pressure to be exposed on a geologic formation zone above or before the ball seat. 
         [0008]    Hydraulic-fracturing equipment used in oil and natural gas fields usually consists of a slurry blender, one or more high-pressure, high-volume fracturing pumps (typically powerful triplex or quintuplex pumps) and a monitoring unit. Associated equipment includes fracturing tanks, one or more units for storage and handling of proppant, high-pressure treating iron, a chemical additive unit (used to accurately monitor chemical addition), low-pressure flexible hoses, and many gauges and meters for flow rate, fluid density, and treating pressure. Chemical additives are typically 0.5% percent of the total fluid volume. Fracturing equipment operates over a range of pressures and injection rates, and can reach up to 15,000 psig (100 megapascals) and 9.4 cu. ft./sec. (265 litres per second) (or about 100 barrels per minute). 
         [0009]    A problem that can be encountered in a fracking operation involves the ball. After the fracking operation is concluded, the surface pressure is restored to a pressure at which the well will flow and produce formation fluids to the surface for recovery. A ball having a low density can be floated or backflowed from the well, but a ball having a low density may be deformed by the pressure differential applied across the ball seat and thereby compromised during fracturing operations. If the ball is of a material that is more dense so that it can not be floated or backflowed from the well to the surface or if it has become deformed, then the ball may present an unwanted obstruction that has to be removed from the well. A workover operation can be implemented in which a drilling instrument is introduced into the well to drill out and mechanically destroy the ball, but a workover operation imposes delays and substantial costs. 
         [0010]    Wells that penetrate extremely deep into the earth&#39;s crust and wells that penetrate formations having a very high pressure may require very high pressures to fracture the formation rock. This requires a ball seat and a ball that can withstand the pressure differential applied thereto. Ball seats are generally made of metal for superior strength, but balls cannot be metal because the density of a metal ball would prevent it from being removed from the well by backflowing the well. The ball seat, when empty, should allow a generally unimpeded flow of fluids through the ball seat. A metal ball would have superior strength, but it would have such a high density that the flow of fluids from the well would not enable the ball to be removed from the well because the ball would not become entrained in the flow to the surface. Conventional plastic balls lack the strength and structural integrity to withstand extreme pressure differentials required for fracking these high pressure formations. More specifically, the pressure differentials required to fracture formations having an extremely high pressure cause conventional plastic balls to implode, rupture or deform to the extent that the seal at the ball seat is lost and the fracking pressure is unachievable. 
         [0011]    What is needed is a ball that has a resistance to deformation so that it can be used in conjunction with a ball seat to reliably isolate geologic formation zones below the ball seat from extremely high fracturing pressures applied to geologic formation zones above and before the ball seat and a density that allows the ball to be broken up or removed from the well by backflowing to as not to present a well obstruction. 
       BRIEF SUMMARY 
       [0012]    One embodiment of the present invention provides a ball for sealing with a ball seat in a well that is constructed to provide resistance to deformation as an extremely high pressure differential is applied to the seated ball and ball seat. An embodiment of the present invention provides a ball that can be deployed to seat in the ball seat, remain in the ball seat during exposure to extremely high pressure differentials there across, and backflowed from or broken up in the well. Embodiments of the ball of the present invention are made of a specially formulated and cast or isostatically pressed ceramic material that provides resistance to deformation under large pressure differentials across the ball and ball seat during fracking operations and favorable density to enable removal of the ball by backflowing or hammering the ball to break it up in the well to prevent an obstacle from remaining in the well. It will be understood that a variety of tools can be run into a well to engage and hammer an isolation ball to break it up into pieces. This enables the use of higher fracking pressures to increase the success of the fracking process. 
         [0013]    One embodiment of the method of making a ball for use with a ball seat to isolate the pressure within a first portion of the well drilled into the earth&#39;s crust from a pressure within a second portion of the well of the present invention includes the steps of mixing and milling a ceramic powder with water, a dispersant and one or more gel-forming organic monomers to serve as a binder to form a mixture, subjecting the mixture to a partial vacuum to remove air from the mixture and to prevent the formation of bubbles that may otherwise result in structural flaws or porosity in the final solidified product, adding a polymerization initiator to the mixture to initiate a gel-forming chemical reaction and to thereby produce a ceramic slurry, adding a catalyst to the ceramic slurry, pouring the ceramic slurry into a molds to cast having a void in the shape of a hollow spherical ball having an opening to receive a plug, heating the mold containing the ceramic gel in a curing oven or a kiln for a period of 30 to 800 minutes at a temperature of 392° F. (200° C.) to 1,472° F. (800° C.), removing the hardened isolation ball from the mold, drying the isolation ball to remove most of the solvent and to minimize warping and cracking, machining the ceramic ball into a spherical shape, firing the ceramic ball, grinding ceramic ball, exposing the ceramic ball to heat for a sustained duration of time in a furnace to burn out the binder and sinter the cast material, air drying the ceramic ball at ambient temperature for 1 to 2 days, firing the ceramic ball in furnace at a temperature ranging from 1600° C. to 1800° C. for a duration of from 1 to 4.5 hours to densify the ceramic, and receiving a plug into a hole in the ball to seal the hollow interior. 
         [0014]    Embodiments of the method of making the ceramic isolation ball may further include the step of using a ceramic powder comprising one of alumina, zirconia-toughened alumina, silicon nitride, tungsten carbide, zirconia, or a bulk metallic glass. 
         [0015]    Embodiments of the method of making the ceramic isolation ball may further include the step of using a monomer comprising one of methacrylamide and hydroxymethlacrylamide. Embodiments of the method of making the ceramic isolation ball may further include the step of using a monomer comprising 3 to 4 weight percent of the of the mixture. 
         [0016]    Embodiments of the method of making the ceramic isolation ball may further include the step of subjecting the mixture to a partial vacuum that is between 300 and 700 mm Hg. 
         [0017]    Embodiments of the method of making the ceramic isolation ball may further include the step of using a polymerization initiator comprising ammonium persulfate. 
         [0018]    Embodiments of the method of making the ceramic isolation ball may further include the step of using a mold into which the ceramic slurry is poured that comprises one of metal, glass, plastic and wax. 
         [0019]    Embodiments of the method of making a ceramic isolation ball may further include the step of using a catalyst comprising Azobis (2-amidinopropane) HCl (AZAP) to cause the monomers in the ceramic slurry to form large cross-linked polymer molecules to trap water within the gel matrix, to produce a rubbery polymer-water gel to immobilize ceramic particles within the slurry and to impart a desired spherical shape to the ceramic slurry of the void of the mold. 
         [0020]    Embodiments of the method of making a ceramic isolation ball may further include the step of adding a catalyst in the amount of 10 weight percent of the ceramic slurry. 
         [0021]    Embodiments of the method of making a ceramic isolation ball may further include the step of drying the isolation ball in air having a relative humidity greater than about 90%. 
         [0022]    Embodiments of the method of making a ceramic isolation ball may further include the step of decreasing the humidity of the surrounding air, and increasing the temperature to speed up the drying step after a shrinkage phase. 
         [0023]    Embodiments of the method of making a ceramic isolation ball may further include the step of applying a pliable coating or pliable cushions to the ceramic isolation ball to provide impact resistance to the ceramic isolation ball as it is transported within the well from the wellhead to the ball seat. The pliable coating or cushion also promotes effective sealing between the isolation ball and the ball seat. The pliable coating or cushion may, in one embodiment of the ceramic isolation ball of the present invention, be from 0.005 inches (0.0127 cm) to 0.05 inches (0.127 cm) in thickness, and may be applied by spraying a liquid product onto the ball and allowing the coating to cure and dry for one hour. 
         [0024]    Embodiments of the method of making a ceramic isolation ball may further include the step of hot isostatic pressing after the last firing step to densify the ceramic material for improved resistance to cracking and to provide superior strength. Embodiments of a method of making the ceramic isolation ball may further include a processing step of casting or injection molding the bulk metallic glass to form the ball. Embodiments of a method of making the ceramic isolation ball may also include the processing step of injection-molding or isostatically pressing a ceramic powder into a spherical shape. 
         [0025]    Embodiments of the method of making a ceramic isolation ball may further include the step of forming a first ceramic hemispherical ball portion and a second ceramic hemispherical ball portion, and the subsequent step of securing a face of the first ceramic hemispherical ball portion to the face of a second ceramic hemispherical ball portion to form the ceramic isolation ball. One embodiment includes the step of securing the first ceramic hemispherical ball portion to the second ceramic hemispherical ball portion using a threadably adjustable fastener with a male member and a female member, wherein the male member includes a shaft with exterior threads and a head, and the female member includes a shaft with interior threads and a head, wherein the head of the male member is secured at an opening of the first ceramic hemispherical ball portion after introducing the shaft of the male member through the opening, wherein the head of the female member is secured at an opening of the second ceramic hemispherical ball portion after introducing the shaft of the female member through the opening, and wherein a distal end of the male member is received into the distal end of the female member and the male member is rotated on its axis relative to the female member to threadably engage the male member to the female member and to adjust the length of the fastener comprised of the male member and female member threadably coupled thereto until the first ceramic hemispherical member is secured at the face to the face of the second ceramic hemispherical member. 
         [0026]    Another embodiment of the method of making a ceramic isolation ball of the present invention includes the steps of forming a first ceramic hemispherical ball portion and a second ceramic hemispherical ball portion, the first ceramic hemispherical ball portion having a face with a plurality radially inwardly protruding threads and the second ceramic hemispherical ball portion having a face with a plurality of radially outwardly protruding threads that correspond in pitch to the radially outwardly protruding threads on the first ceramic hemispherical ball portion. The face of the first ceramic hemispherical ball portion can be engaged with the face of the second ceramic hemispherical ball portion, and the second ceramic hemispherical ball portion can be rotated to make up the threads on the first ceramic hemispherical ball portion with the corresponding threads on the second ceramic hemispherical ball portion to couple the first and second ceramic hemispherical ball portions to form a ceramic isolation ball. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0027]      FIG. 1  is a sectional view of a well drilled into the earth&#39;s crust and illustrating a series of hydraulic fractures disposed at a predetermined spacing to enhance production and recovery of formation fluids from a hydraulically fractured subsurface geologic formation. 
           [0028]      FIG. 2  is the sectional view of the well of  FIG. 1  illustrating the lack of fractures within the targeted geologic formation prior to the creation of the hydraulic fractures and illustrating a location of a desired placement of a ball and a ball seat to receive the ball to thereby isolate zones deeper in the well than the ball seat (to the right) from zones shallower in the well than the ball seat (to the left). 
           [0029]      FIG. 3  is a sectional elevation of an embodiment of a ball of the present invention received in a ball seat set within the casing of the drilled well illustrated in  FIG. 2  to create an isolating seal. 
           [0030]      FIG. 4  is a perspective view of one embodiment of a hollow, cast ceramic ball of the present invention. 
           [0031]      FIG. 5  is a perspective view of a stainless steel plug for use in closing the opening of the embodiment of the ball of  FIG. 4 , the plug having spring-biased legs extending from an interior side of a plug cap. 
           [0032]      FIG. 6  is an exploded view of an embodiment of a hollow, cast ceramic ball of the present invention comprising two hemispheres securable one to the other to form a ball by a fastener. 
           [0033]      FIG. 7  is a sectional assembled view of the ball components of  FIG. 6 . 
           [0034]      FIG. 8  is a view of an embodiment of a hollow, cast ceramic ball of the present invention comprising two hemispheres that are securable one to the other to form a ball by threads. 
           [0035]      FIG. 9  is an assembled view of the ball components of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    One embodiment of the present invention provides a ball having an outer surface of sufficient smoothness to enable the ball to seat within and to seal with a ball seat, wherein the ball has substantial resistance to deformation by an applied pressure differential across the seal created by the ball received within the ball seat. The embodiment of the ball of the present invention can include a solid or, preferably, a hollow interior. 
         [0037]    The manner in which an embodiment of the ball of the present invention is made may vary, but will generally include the steps of gel-casting, slip-casting, isostatic pressing, injection molding and/or hot isostatic pressing (HIP) a ceramic powder into a ball shape. A hollow ball will typically have an entry hole which is made necessary by the casting process. 
         [0038]    One embodiment of the hollow ceramic isolation ball of the present invention is made by mixing and milling a ceramic powder including alumina, zirconia-toughened alumina (ZTA), silicon nitride, tungsten carbide or zirconia, with water, a dispersant and one or more gel-forming organic monomers such as, for example, methacrylamide or hydroxymethlacrylamide (HMAM) to serve as a binder. The binder is preferably included in the range from 3 to 4 weight percent of the mixture. The mixture is subjected to a partial vacuum, preferably between 300 to 700 mm Hg, to remove air from the mixture and to prevent the formation of bubbles that may otherwise result in structural flaws or porosity in the final solidified product. A polymerization initiator such as, for example, ammonium persulfate, is added to the mixture to initiate a gel-forming chemical reaction and to thereby produce a ceramic slurry. The ceramic slurry is poured into molds of metal, glass, plastic or wax to cast the ceramic gel into the shape of a hollow spherical ball having an opening to receive a plug or cap. 
         [0039]    The molds containing the cast ceramic gel are heated in a curing oven or a kiln. A catalyst such as, for example, 10 weight percent Azobis (2-amidinopropane) HCl (AZAP) causes the monomers in the ceramic slurry to form large cross-linked polymer molecules that trap water within the gel matrix, thereby providing a rubbery polymer-water gel. The gel permanently immobilizes the ceramic particles in the desired shape defined by the interior of the mold in which the ceramic gel is contained. Finally, the hardened isolation ball is removed from the mold. 
         [0040]    The cast ceramic isolation ball is allowed to dry thoroughly to remove most of the solvent. It is preferable that the ball is allowed to dry at a high relative humidity (greater than about 90%) to minimize warping and cracking. During the drying step, a ceramic slurry that is about 50 weight percent solids will uniformly shrink in size by about 3%. The humidity of the surrounding air may be decreased and the temperature may be increased to speed up the drying step after the shrinkage phase is completed. 
         [0041]    The resulting gel-cast ceramic ball is sufficiently soft that can be “green-machined” using tungsten carbide or steel tools. Green machining is machining the ceramic into a preferred shape prior to firing the ceramic ball. Once the ceramic is fired, the resulting ball can only be ground using diamond tooling, which is costly and time consuming. In the “green” state, machining is inexpensive and quick. 
         [0042]    The final steps include the burning out of the binder and the sintering of the cast material. These two steps may be combined into a single step. The ceramic ball is allowed to air dry 1 to 2 days, and is then fired in furnace at a temperature ranging from 1600° C. to 1800° C. This heating procedure accomplishes two goals. First, water is removed as the ball dries. Second, water in the ball causes cracking during exposure to furnace heat. An initial temperature ramp to 1,022° F. (550° C.) enables the polymer remaining in the ceramic material to burn out. Removing the polymer from the ceramic material is required to prevent defects and cracks and enables densification of the ceramic body. Second, at the higher temperature from 1600° C. to 1800° C., the intense heat of the furnace sinters the ceramic to make it hard and dense. 
         [0043]      FIG. 1  is a sectional view of a well  20  drilled from the surface  21  into the earth&#39;s crust  29  and illustrating a series of hydraulic fractures  26  disposed at a predetermined spacing  28  to enhance production and recovery of formation fluids from a hydraulically fractured subsurface geologic formation  24 . The drilled well  20  may include multiple layers of surface casing as is known in the art. The drilled well  20  may include one or more turns or changes in direction to align the portion of the well  20  to be perforated or otherwise to gather fluids within a known geological structure, seam or formation  24 . The fractures  26  created in the formation  24  are generally disposed at a predetermined spacing  28  selected for optimal drainage. The targeted formation  24  may reside between a top layer  22  and an underlying layer  23  within the earth&#39;s crust  29 . It will be understood that fluids entering the well  20  flow according to a pressure gradient in the direction of the arrow  27  to the surface for processing, storage or transportation. 
         [0044]      FIG. 2  is the sectional view of the well  20  of  FIG. 1  illustrating the lack of fractures  26  (seen in  FIG. 1 ) within the targeted geologic formation  24  prior to the creation of the hydraulic fractures shown in  FIG. 1 .  FIG. 2  illustrates a location of a desired placement of a ball (not shown) and a ball seat (not shown) to receive the ball to thereby isolate a zone  50  that is deeper in the well than the ball seat (i.e., to the right) from a zone  51  that is shallower in the well  20  than the ball seat (i.e. to the left). It will be understood that the ball and ball seat are to be placed in a portion of the casing  12  that lies within the targeted geologic formation  24  and that the pressure at any given location within the well  20  is approximately equal to the pressure at a wellhead  49  at the surface  21  plus the product of the vertical elevation change  46  times the density (as measured in units corresponding to the unit used to measure depth) of a fluid residing in the well  20 , assuming that the well  20  is filled with the fluid. 
         [0045]      FIG. 3  is a sectional elevation of an embodiment of a ball  10  of the present invention received in a ball seat  14  set within a section of a casing  12  of the drilled well  20  (not shown in  FIG. 3 ) illustrated in  FIG. 2  to create an isolating seal. It will be understood that a number of tools exist for setting the ball seat  14  within the portion of the casing  12  in which the seal is to be affected, and that those tools and the methods of setting those tools are not within the scope of the present invention, and that  FIG. 3  is provided merely to illustrate the manner in which an embodiment of a ball  10  engages the ball seat  14  after the ball seat  14  is set in the portion of the casing  12  and after the ball  10  is introduced into the well  20  and moved to the ball seat  14 . 
         [0046]      FIG. 4  is an elevation view of a hollow, cast ceramic ball of the present invention. 
         [0047]      FIG. 4  is a sectional view of an embodiment of a ball  10  of the present invention. The ball  10  of  FIG. 4  comprises a hollow interior  19 , an exterior surface  17 , a hole  18  in the exterior surface  17 . 
         [0048]      FIG. 5  is a perspective view of a stainless steel plug  11  having spring-biased legs  16  extending from an interior side of a plug  11 . The plug  11  is preferably comprised of stainless steel but can be made of most alloys or metals. The plug  11  of  FIG. 5  is shown aligned with the hole  18  in the ball  10  for being fitted into the hole  18  to close the hole  18  and to seal the hole  18  against fluid intrusion so that the ball  10  can maintain a desired effective density. It will be understood that, absent a seal at the plug  11  received into the hole  18 , the hollow interior  19  of the ball  10  will fill with fluid, thereby making the ball  10  heavier and thereby adversely affecting the effective density of the ball  10 . 
         [0049]    The embodiment of the ball  10  illustrated in  FIGS. 3-5  seals against the ball seat  14  (see  FIG. 3 ) to isolate formation zones below the ball seat  14  from the one or more formation zones above the ball seat  14  to allow the zones above the ball seat  14  to be fractured without affecting the zones below the ball seat  14 . 
         [0050]    The configuration of the well  20  and the depth at which the ball seat  14  and the ball  10  are to be used determine the size of the ball seat  14  and the ball  10 . The range of sizes of the ball  10  may be within the range from 1.75 inches (4.45 cm) to 4 inches (10 cm), or larger. The size of the hole  18  in the hollow ball  10  can, in one embodiment, range from 0.2 inches (5 mm) to 1 inch (25.4 mm). 
         [0051]      FIG. 6  is an exploded view of an embodiment of a hollow, cast ceramic ball  10  of the present invention comprising two hemispheres  30  and  60  securable one to the other to form a ball  10  by a fastener comprising a male member  70  and a female member  80 . The upper hemisphere  60  in  FIG. 6  includes an opening  64  to receive the distal end  75  and the externally threaded shaft  73  of the male member  70 . The male member  70  further includes a head  72  at a proximal end  71  of the male member  70  to engage the hemisphere  60 . The lower hemisphere  30  in  FIG. 6  includes an opening (not shown) opposite to the opening  64  of the upper hemisphere  60  to receive the distal end  85  and internally threaded shaft  84  of the female member  80 . The female member  80  further includes a head  82  at a proximal end  81  of the female member  80  to engage the hemisphere  30 . The pitch of the threads  74  along the threaded shaft  73  of the male member  70  correspond to the pitch of the internal threads  87  within the shaft  84  of the female member  80 , and the distal end  75  of the male member  70  can be received within the distal end  85  of the female member  80  and the male member  70  can then be rotated relative to the female member  80  to threadably couple the male member  70  to the female member  80 . It will be understood that the head  72  at the proximal end  71  of the male member  70  will be adducted to the head  82  at the proximal end  81  of the female member  80  as the male member  70  and the female member  80  are threadably made up, and the two hemispheres  30  and  60  will be secured one to the other by making up the threaded connection between the male member  70  and the female member  80 . Optionally, the mating faces  39  and  69  of the lower hemisphere  30  and the upper hemisphere  60 , respectively, may include mating profiles such as, for example, a protruding lip  38  on the face  39  of the lower hemisphere  30  that is received into a corresponding recess  68  (not shown on FIG.  6 —see  FIG. 7 ) on the face  69  of the upper hemisphere  30 . 
         [0052]      FIG. 7  is a sectional assembled view of the ball  10  components of  FIG. 6 . The distal end  75  of the male member  70  can be seen in dotted line form received within the distal end  85  of the female member  80 . 
         [0053]      FIG. 8  is a view of an embodiment of a hollow, cast ceramic ball  10  of the present invention comprising two hemispheres  90  and  97  that are securable one to the other to form a ball  10  by threads  92 . The lower hemisphere  97  in  FIG. 8  includes a face  95  having a protruding lip  99  and threads  92  disposed on a radially outwardly portion  94  of the protruding lip  99 . The face  101  of the upper hemisphere  90  (not shown in FIG.  8 —see  FIG. 9 ) includes a recess  102  (not shown in  FIG. 8 ) that corresponds to and receives the protruding lip  99  of the lower hemisphere  97  upon assembly. An interior portion  103  of the recess  102  of the upper hemisphere  90  includes threads  91  that correspond to and mate with the threads  92  on the protruding lip  99  on the lower hemisphere  97 . 
         [0054]      FIG. 9  is an assembled view of the ball  10  components of  FIG. 8 . The threads  91  on the interior portion  103  of the recess  102  of the upper hemisphere  90  are seen as being made up with the threads  92  on the radially outwardly portion  94  of the protruding lip  99  of the lower hemisphere  97  to secure the upper hemisphere  90  to the lower hemisphere  97 . 
         [0055]    Embodiments illustrated in  FIGS. 1-9  are not to be considered as limiting of the scope of the present invention, which is limited only by the claims that follow. 
         [0056]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components and/or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. 
         [0057]    The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.