Abstract:
An embodiment of a fracking ball cooperates with a ball seat to isolate a well first portion of an earthen well drilled into the earth&#39;s crust from a well second portion and comprises an interior chamber to receive an explosive charge. The explosive charge may be surrounded by a filler material that is resistant to deformation. A pressure sensor, a circuit, and a battery are also received into the chamber. The ball material, may comprise one of zirconium oxide, aluminum oxide, bulk metallic glass, silicon nitride or tungsten carbide, and the ball is resistant to deformation within the ball seat under the application of a substantial pressure differential across the ball and ball seat. Detonation of the explosive charge fragments the ball to prevent the ball from presenting an obstruction to subsequent well operations. A safety fuse may be included to enable safe handling and transport.

Description:
STATEMENT OF RELATED APPLICATIONS 
       [0001]    This application depends from and claims priority to U.S. Provisional Application No. 61/898,088 filed on 31 Oct. 2013. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an improved sacrificial isolation ball for use with a ball seat to fluidically isolate a targeted geologic zone for hydraulic fracturing operations to enhance production of hydrocarbons from a well drilled into the targeted geologic zone. 
       BACKGROUND OF THE RELATED ART 
       [0003]    Hydraulic fracturing is the fracturing of rock by a pressurized liquid. Some hydraulic fractures form naturally. Induced hydraulic fracturing or hydro-fracturing, commonly known as “fracking,” is a technique in which a fluid, typically water, is mixed with a prop-pant and chemicals to form a mixture that is injected at high pressure into a well to create small fractures in a hydrocarbon-bearing geologic formation along which the hydrocarbon fluids such as gas, oil or condensate may migrate to the well for production to the surface. Hydraulic pressure is removed from the well, then small grains of the proppant, for example, sand or aluminum oxide, hold the fractures open once the formation pressure achieves an equilibrium. The technique is commonly used in wells for shale gas, tight gas, tight oil, 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 rates and well productivity. 
         [0004]    A hydraulic fracture is formed by pumping fracturing fluid into the well at a rate sufficient to increase pressure downhole at the target 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. 
         [0005]    The location of one or more fractures along the length of the borehole is strictly controlled by various methods that create or seal off boles in the side of the well. A well may be fracked in stages by setting a ball seat below the geologic formation to be fracked to isolate one or more lower geologic zones open to the well from the anticipated pressure to be later applied to a zone closer to the surface. A ball of a predetermined diameter is introduced into the well at the surface and pumped downhole. When the ball reaches the ball seat installed in the bore of a casing, the ball seats in the ball seat to form a seal that isolates geologic formation zones below the ball seat from the anticipated hydraulic fracturing pressure to be exposed on a geologic formation zone above the ball seat. 
         [0006]    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 quintuples 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 100 megapascals (15,000 psi) and 265 litres per second (9.4 cu. ft./sec or 100 barrels per min.). 
         [0007]    A problem that can be encountered in a fracking operation involves the impairment to subsequent operations that can result from the presence of 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 fracking ball having a sufficiently low density can be floated or back-flowed from the well, but a ball having a low density may be deformed by the large pressure differential applied across the ball and 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 back-flowed from the well to the surface, then the ball may present an unwanted obstruction that has to be removed from the well to prevent impairment of subsequent well operations. 
         [0008]    A workover operation can be implemented in which a drilling instrument is introduced into the well to drill out and to mechanically destroy the ball, but a workover operation requires that a workover rig be brought to the surface location of the well for downhole operations. The need for the rental, transportation, rigging up and use of a rig imposes substantial delays and substantial costs. 
         [0009]    What is needed is a fracking ball that has a sufficient density and 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 anticipated large fracturing pressures applied to geologic formation zones above the ball seat and that does not impair subsequent well operations. 
       BRIEF SUMMARY 
       [0010]    One embodiment of the present invention provides a fracking ball for sealing with a ball seat in a well. The fracking ball contains an explosive charge for fragmenting the fracking ball after use. The fracking ball is constructed in a manner that provides sufficient resistance to deformation of the ball as a large pressure differential is applied across the ball and the engaged ball seat. 
         [0011]    An embodiment of the present invention provides a fracking ball that can be fragmented by detonation of an explosive charge provided within an interior chamber of the ball to produce, upon detonation of the explosive charge, a plurality of ball fragments that do not interfere with subsequent well operations. In one embodiment, the use of a ceramic spherical body provides sufficient resistance to fracking ball deformation under large pressure differentials across the fracking ball and ball seat applied during fracking operations. In addition, these materials can provide for favorable fragmentation of the ball upon detonation of the explosive charge stored within an interior chamber of the ball to prevent unwanted obstacles having a substantial size from obstructing flow in the well. 
         [0012]    In one embodiment of the ball of the present invention, a battery, a pressure sensor and a circuit are included within the interior chamber of the fracking ball along with the explosive charge. The pressure sensor is disposed in fluid communication with an exterior surface of the ball through an aperture in the ceramic structure. The pressure sensor detects a predetermined pressure threshold and initiates a predetermined timer delay period prior to detonation. Upon elapse of the predetermined timer delay period, a circuit is completed that generates an electrical current from the battery to the explosive charge to detonate the explosive charge and to thereby fragment the ball. In one embodiment in which the ball is a dissolvable ball, the fragmentation of the ball dramatically increases the aggregated surface area exposed to the fluids in the well to provide a much more rapid rate of dissolution as compared to a dissolvable ball that is not fragmented. 
         [0013]    The higher fracking pressures achievable by use of embodiments of the fracking ball of the present invention, along with the lack of obstruction of subsequent well operations due to fragmentation, increase the success and effectiveness of the fracking process, lowers or eliminates workover rig rental costs, and prevents unwanted delays in subsequent well operations after the fracking process. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]      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. 
           [0015]      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). 
           [0016]      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. 
           [0017]      FIG. 4  is a sectional view of an embodiment of a ball of the present invention. 
           [0018]      FIG. 5  is a sectional view of an alternate embodiment of a ball of the present invention. 
           [0019]      FIG. 6  is an illustration of the fragments resulting from the detonation of the explosive charge contained within the interior chamber of the ball of the present invention. 
           [0020]      FIG. 7  is an illustration of a safety feature that may be used to enhance the safety of personnel that may handle, prepare and deploy an embodiment of the ball of the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0021]    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 contains an explosive device that can be detonated to destroy the ball from within and to thereby fragment the ball into a large plurality of small fragments. The embodiment of the ball may include a filler material received within the hollow interior of the ball, along with the explosive device, wherein the filler material comprises a non-compressible fluid such as, for example, a gel, or particles or pieces of such a small size that they can be released in the well without concern for the particles or pieces interfering with the function or operation of any downhole components that might be contacted. The filler material may comprise one of sand, ceramic beads or some other filler material that exhibits substantial resistance to deformation and resistance to compression. The filler material may also comprise an incompressible fluid, such as water. It will be understood that the temperature at which the ball will reside prior to detonation of the explosive charge should be considered when choosing a filler material as an incompressible fluid may result in excessive internal pressure at elevated temperatures. 
         [0022]    The manner in which an embodiment of the fracking ball of the present invention is made may vary, but will generally include the steps of providing a ceramic outer shell having a hollow interior and, optionally, a hole through which a pressure sensor may be inserted into the fracking ball. An embodiment of a fracking ball of the present invention may include an explosive device and a filler material that can be disposed within the hollow interior. In one embodiment of the ball, a first hemispherical portion and a second hemispherical portion are secured together to form a spherical ball. 
         [0023]    In one embodiment, a ceramic sphere may consists of two or more pieces secured together to form a spherical body. In another embodiment the ceramic sphere consists of a unitary spherical body having a hole for insertion of a safety fuse such as, for example, a pressure sensor, to enable the explosive charge and the timer-controlled detonator. It will be understood that the pressure sensor may be provided to generate a signal that enables or initiates the circuit that ultimately delivers the detonating current flow from the battery to the explosive charge, and that the provision of the pressure sensor to complete and thereby enable the fracking ball circuit would cause the pressure sensor to function as a safety fuse without which the fracking ball would be unable to self-destruct. 
         [0024]    In one embodiment, the ceramic ball may comprise one of zirconium oxide, silicon nitride, tungsten carbide, zirconia toughened alumina, bulk metallic glass (BMG) and aluminum oxide. The high compressive strengths of these ceramic materials enable the fracking ball to seat in the ball seat and to cooperate with the ball seat to isolate deeper well zones from shallower well zones to be fracked. This requires the ball and ball seat to withstand a very high fracking pressure on an uphole side of the ball and a substantially lower pressure on a downhole side of the ball. Embodiments of the ceramic fracking ball of the present invention may be manufactured by, for example, but not by way of limitation, isostatic pressing, hot isostatic processing (HIP), injection molding, slip casting or gel casting techniques. In one embodiment, a ball comprising zirconia with a very thin wall thickness of only 0.060 inches can be gel cast and subsequently hot isostatically pressed to increase the flexural strength of the fracking ball so it can be seated m the ball seat to withstand very high differential pressures while yielding less debris material subsequent to fragmentation by the explosive charge. Less debris material will result in a much lower probability of any debris for fragments of a size sufficient to interfere with or obstruct equipment to be used in fracking other, deeper or lower zones. 
         [0025]      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 proposed 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. 
         [0026]      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, using a circle, 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  62  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. 
         [0027]      FIG. 3  is a sectional elevation of an embodiment of a ball  10  of the present invention received in a ball seat  44  that has been previously set within a section of a casing  62  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  44  within the portion of the casing  62  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.  FIG. 3  is provided merely to illustrate the manner in which an embodiment of a ball  10  moves through the bore  70  of the casing  62  to engage the ball seat  44  after the ball seat  44  is set in the portion of the casing  62  and after the ball  10  is introduced into the well  20  and moved to the ball seat  44 . The ball  10  and ball seat  44  together form a seal to isolate a lower portion of the bore  71  from the upper portion of the bore  70  that is uphole to the ball  10  and ball seat  44 . 
         [0028]      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 consisting of a hollow interior  15  of a first hemispherical portion  11  and a hollow interior  16  of a second and matching hemispherical portion  12 . The circular rim  13  of the first hemispherical portion  11  is manufactured to correspond in shape for mating engagement with the circular rim  14  of the second hemispherical portion  12 . Securing of the first hemispherical portion  11  to the second hemispherical portion  12  provides a spherical ball having an exterior surface consisting of the exterior surface  17  of the first hemispherical portion  11  and the exterior surface  18  of the second hemispherical portion  12 . 
         [0029]      FIG. 5  is a plan view of a hollow interior  15  of the first hemispherical portion  11  of  FIG. 4 . An aperture  30  in the ceramic hemispherical shell  11  is fluidically connected by a conduit  31  to a pressure sensor  32 . The pressure sensor  32  closes a switch upon sensing a predetermined threshold pressure through the aperture  30  and the conduit  31 . 
         [0030]    Upon receiving the signal from the pressure sensor  32 , a timer is activated. After a predetermined amount of time from activation, a signal is sent to a detonator to explode the explosive charge within the fracking ball. Upon detonation of the explosive charge  36 , the outer shell of the fracking ball  10  is fragmented. 
         [0031]      FIG. 6  illustrates a fragmented ceramic ball  10 A as it might appear immediately after the moment of detonation of the explosive charge  36  within a hollow interior of the fracking ball  10  to fragment the ball  10  into numerous ball fragments  49 , which are then dispersed into well fluids moving throughout the interior bore of the casing  62 . It will be understood that such fragmentation dramatically increases the cumulative surface area of the ball fragments  49  exposed to the fluids in the well. This will provide a correspondingly dramatic increase in the rate at which any dissolvable material will degrade and dissolve in the fluids in the well. 
         [0032]      FIG. 7  illustrates a safety feature that may be used to enhance the safety of personnel that may handle, prepare and deploy an embodiment of the ball  10  of the present invention.  FIG. 7  illustrates the first hemispherical portion  11  of the ball  10  having a fuse aperture  52  to receive the safety fuse (such as a pressure sensor)  53 . Upon deployment of the ball  10  from the surface, the safety fuse  53  can be inserted into and through the fuse aperture  52  to engage and enable a critical connection. For example, but not by way of limitation, the safety fuse  53  may be inserted and seated in the fuse aperture  52  to engage, within the hollow interior  15  of the ball  10 , a pair of conductive leads bridged by the safety fuse  53  that completes an electrical circuit that will later, after the pressure sensor  32  senses the threshold pressure and after the delay period has run, enable the battery  40  to detonate the preliminary explosive charge  35 . Alternately, the safety fuse  53  may engage and enable the circuit  33  so that, upon detection of the threshold pressure by the pressure sensor  32 , the circuit  33  will begin the delay period. It will be understood that there are various ways of enabling the explosive charge using a safety fuse  53 , that multiple safety fuses  53  may be used. In one embodiment, no safety fuse  53  is used, but this is not recommended for obvious reasons. In the embodiment illustrated in  FIG. 7 , the safety fuse  53  comprises an enlarged head  54  that limits the extent to which the safety fuse  53  can be inserted through the fuse aperture  52 . This head  54  and the safety fuse  53  length may be customized to precisely position the safety fuse  53  relative to the other components  31 ,  32 ,  33 ,  34 ,  35 ,  36  and  40  within the fracking ball  10 . 
         [0033]    The configuration of the well  20  and the depth at which the ball seat  44  and the ball  10  are to be used determine the size of the ball seat  44  and the ball  10 . The range of sizes of the ball  111  may be within the range from 4.45 cm (1.75 inches) to 10 cm (4.0 inches), or larger. The filler material, if any, may comprise particles or beads that vary in size and material, but are preferably in the range from 0.2 mm (0.008 inch) to 1 mm (0.04 inch) diameter. A noncompressible fluid, such as a gel, can also be used as the filler material. 
         [0034]    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. 
         [0035]    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.