TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to barriers for sealing zones in subterranean wells and, more particularly, to composite fracturing balls and methods of use.

SUMMARY OF THE INVENTION

The present invention is directed to a barrier for substantially sealing a zone in a subterranean formation, the barrier comprising a body and a projection connectable with the body.

The present invention further is directed to a system for substantially sealing a zone in a subterranean formation, the system comprising a barrier, wherein the barrier comprises a body, and a projection connectable with the body.

The present invention further is directed to a method of substantially sealing a zone in a subterranean formation, the subterranean formation comprising at least one seat. The method comprises the steps of orienting a barrier comprising a body and a projection connectable with the body so that the barrier is substantially sealingly receivable in the seat.

The present invention further is directed to a method of substantially sealing a zone in a subterranean formation, the subterranean formation comprising at least one seat, the method comprising the steps of orienting a barrier comprising a body and a magnet so that the barrier is substantially sealingly receivable in the seat.

The present invention further is directed to a system for substantially sealing a zone in a subterranean formation. The system comprises a body and a magnet connectable with the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a fracturing ball comprised of a randomly oriented, fiber reinforced composite material.

FIG. 2A illustrates a perspective view of a bidirectional cloth layered laminate composite material used to manufacture fracturing balls.

FIG. 2B illustrates a perspective view of bidirectional rolled cloth layered composite material used to manufacture fracturing balls.

FIG. 3A illustrates a cross sectional view of a composite fracturing ball with randomly oriented fibers, the fracturing ball situated with the parting line oriented in line with or parallel with the direction of flow of fluids z in the well.

FIG. 3B illustrates a cross sectional view of a composite fracturing ball with interlaminate plies, the fracturing ball situated so that interlaminate plies are oriented in line with or parallel with the direction of flow of fluids in the well.

FIG. 3C illustrates a cross sectional view of a composite fracturing ball with randomly oriented fibers, the fracturing ball situated with some fibers or the parting line oriented perpendicular to the direction of flow of fluids in the well.

FIG. 3D illustrates a cross sectional view of a composite fracturing ball with interlaminate plies, the fracturing ball situated so that interlaminate plies are oriented perpendicular to the direction of flow of fluids in the well.

FIG. 4 is a schematic drawing of a borehole illustrating a well bore in which an exemplar of a fracturing ball of the present invention is situated.

FIG. 5 is a schematic drawing of a borehole illustrating a well bore in which an exemplar of a fracturing ball of the present invention is situated in a vertical well bore or a horizontal well bore.

FIG. 6 shows a geometry of an exemplar of the body and the projection of fracturing ball of the present invention.

FIG. 7A is a perspective view of an exemplar of a projection of the fracturing ball of the present invention illustrating a sample orientation of the fracturing ball on the seat.

FIG. 7B is a perspective view of an exemplar of a projection of the fracturing ball of the present invention illustrating a sample orientation of the fracturing ball on the seat.

FIG. 8 illustrates an embodiment of a projection of an exemplary fracturing ball of the present invention wherein the projection comprises an extension.

FIG. 9 illustrates an alternative embodiment of an exemplary fracturing ball of the present invention wherein the projection comprises an extension.

FIG. 10 illustrates an alternative embodiment of a projection of an exemplary fracturing ball of the present invention.

FIG. 11 illustrates an alternative embodiment of a projection of an exemplary fracturing ball of the present invention.

FIG. 12 illustrates an alternative embodiment of a projection of an exemplary fracturing ball of the present invention.

FIG. 13 illustrates an alternative embodiment of a projection of an exemplary fracturing ball of the present invention.

FIG. 14 illustrates an alternative embodiment of an exemplary fracturing ball of the present invention comprising a magnet.

DETAILED DESCRIPTION OF THE INVENTION

Graduated ball drop systems are used in oil and gas field operations for various purposes, such as isolating a zone in a subterranean well for fracturing or stimulation treatment. Certain of these systems typically employ a series of underground sliding sleeves and are applicable in horizontal, vertical or deviated wells. The sliding sleeve is set in motion by a ball inserted into the well from the surface via pump, gravity or other transport, to a desired depth and location in the well. When the ball reaches a predetermined location, it engages a sealing seat, thereby creating pressure that moves the sleeve and acting as a barrier to isolate the subterranean formation beyond the location of the ball.

Various types of balls, often called fracturing or frac balls, can be used in graduated ball drop systems. These balls are made of a variety of materials, including metals, metal alloys, resins, composites and other non-metallic substances. The material chosen for any particular application is in part a function of the desired compressive strength of the ball. It also is desirable to choose a material that facilitates removal of the ball from the seat following completion of well stimulation or other treatment. To that end, nonmetallic materials create a lighter weight, more maneuverable ball and are easier to remove from the seat during flowback operations or clean up. Balls made from non-metallic materials also can be purposefully susceptible to rupture, dispersion or dissolution in well fluids, which further facilitates removal from the seat and well.

Consequently, non-metallic materials provide benefits over metals and metal alloys in graduated ball drop systems. Such non-metallic materials include reinforced layered or rolled laminate or polymer matrices that are reinforced with glass or carbon strands or fibers. While these materials provide desirable physical properties and produce effective results, they still do not entirely satisfy the requirements needed for frac balls in high pressure fracturing processes.

In order to be effective, frac balls must withstand high pressures. To date, the highest performing non-metallic frac balls are machined from composite materials with fiber reinforcements. The reinforcements in these composite materials may be formed from materials having reinforcing fibers randomly oriented in a bonding matrix, such as from a sheet molding compound or bulk molding compound, as shown in FIG. 1. Random fiber composite materials have a bulk factor that is compressed during the molding process, and some fibers naturally will orient during the molding compression process. Additionally, the reinforcements in these composite materials may already be directionally oriented with an epoxy compound and bidirectional glass fiber laminate, as illustrated in FIG. 2A, or bidirectional fiber fabric that is rolled and cured into rod stock, as shown in FIG. 2B. Other manufacturing methods, such as injection, transfer and compression molding, with or without fiber reinforcement, will also orient material structures to produce a desired direction on the sealing seat. Each of these stock materials comprises reinforcing material with a bonding matrix or layer. The materials properties in plate fabric composites are oriented along x and y axes as shown in FIG. 2A, while for rod stock, the material properties are oriented in the axial direction x and circumferential direction y, illustrated in FIG. 2B.

Composite frac balls, whether machined from billet, flat or round stock, have proven to be stronger in one direction versus another. When loaded in the direction that puts in shear, for example, the (1) interlaminate plies of the composite material, (2) the parting line of the molded frac ball (3) or the fibers themselves, whether chopped and/or continuous, as shown in FIGS. 3A and 3B, the frac ball may be prone to failure or delamination at lower pressures. FIG. 3A illustrates a conventional in situ composite frac ball formed from molding compound and situated on a sealing seat with the parting line of the frac ball oriented in line with the direction of flow z of fluids in the well. FIG. 3B illustrates a conventional frac ball made of cloth materials situated on the sealing seat with the interlaminate plies oriented generally in line or parallel with the direction of flow of the well. In either case, the frac ball is prone to failure or delamination in these orientations.

Composite frac balls generally perform better when the points that are susceptible to shear are oriented generally perpendicular to the direction of flow of fluids, shown by arrow z in the well in FIGS. 3C and 3D. Thus, while composite frac balls provide significant advantages over metals and other materials, they are susceptible to failure when not positioned in a desired orientation on the sealing seat.

Frac balls made from composite materials can only be performance rated based on test data generated from the balls employed in the least desired position on the seat, because heretofore orientation of the ball downhole was uncontrollable. Consequently, there is a need for an orientable composite frac ball that enables consistent orientation in a desired position on the sealing seat downhole.

The present invention provides an orientable frac ball, system and method of use that position the ball in a desired orientation on the sealing seat, thus avoiding the above-described problems. Desired orientation can be accomplished by altering the geometry of the ball with one or more features that can be molded with or added to the ball. A projection of any geometry on a ball, with a length plus ball diameter that is greater than the diameter of well bore, will prevent the ball from orienting in an undesired position on the seat. This projection may be made of a variety of materials that can break or disintegrate at the appropriate time when removing the frac ball from the well bore. During the pump back process in which the frac ball will move up the well through the progressively larger sealing seats, the projection will break away and should not hinder the removal process. The projection may comprise failure points for strategically breaking the projection during specified operations such as pump back. These frac balls can be dropped with the tail down or tail up. As an alternative to a projection, a magnet strategically placed in the frac ball can orient the ball on a metal seat by magnetic attraction with the sealing seat. These and other advantages of the present invention will be apparent from the following description of the invention.

Turning now to the drawings in general, and to FIG. 4 in particular, there is shown therein a schematic of an earth formation 10 in which an exemplar of a barrier or frac ball 12 of the present invention is shown situated in well 14. The invention may comprise a plurality or system of barriers or frac balls 12. The terms â€œbarrier,â€ â€œfracturing ballâ€ and â€œfrac ball,â€ and plurals thereof, are used interchangeably herein to describe a mechanical diversion for sealing perforations in a subterranean formation and/or for diverting fluids. While FIG. 4 depicts a vertical well, it will be appreciated that the frac ball of the present invention may be used in deviated wells and horizontal wells, as shown in FIG. 5.

With continuing reference to FIGS. 4 and 5, and turning also to FIGS. 6, 7A and 7B, the frac ball 12 of the present invention comprises a body 18 and a projection 20. The body 18 of frac ball 12 is receivable in a seat 16 positioned in well 14, in a manner that is yet to be described. To that end, the frac ball 12 may be any shape that permits sealing engagement with the seat 16. Conventional seats available on the market typically form a round indentation for receiving a frac ball. Accordingly, for conventional sealing seats 14, frac ball 12 must four at least a semi-spherical shape on the bottom portion of the frac ball where it engages the seat 16. It will be appreciated, however, that the shape of frac ball 12 may be manufactured to any specification necessary to mate with the seat 16 in use at a particular well.

The body 18 of frac ball 12 may be comprised of any material suitable for use downhole in well 14, including fiberglass, carbon, polymers, plastics, thermoplastic resins, thermoset resins, metals, metal alloys, cloth, composites and combinations of the foregoing. In one embodiment of the invention, the body 18 of frac ball 12 comprises a reinforcing material of chopped glass or carbon fibers in a bismaleimide (BMI) resin matrix. In another embodiment of the invention, the body 18 of frac ball 12 comprises a laminated composite material of fiberglass cloth and epoxy or phenolic compound. It will be appreciated that the body 18 may be comprised of any materials suitable to the particular pressures, temperatures, fluids and other conditions at the well 14 where in use. Although the frac ball of the present invention can be sized to any application, the diameter of body 18 of frac ball 12 may range from about 0.75 inches to about 4 inches. The body 18 generally has a density of from about 62 lb/ft³(1 g/cm³) to about 500 lb/ft³(7.85 g/cm³).

With continuing reference to FIGS. 6, 7A and 7B, the material properties of frac ball 12, when comprised of composite materials, are anisotropic and, therefore, fluctuate based upon orientation of the frac ball in the seat 16. Accordingly, the body 18 of frac ball 12 is provided with a projection 20 that alters the geometry of the frac ball. The projection 20 may be any shape, such as a hollow or solid rod, or any other symmetric or asymmetric extension. For example, FIG. 8 depicts a hollow cone for projection 20A further comprising extension 22. FIG. 9 illustrates a projection 20A comprising a star-shaped extension 22. Other shapes, such as a dart tail, for example, also would alter the geometry of the frac ball 12.

The geometry of the projection 20 helps achieve the desired orientation of the frac ball 12 on the sealing seat 16. As shown in FIG. 6, the length of the projection 20 (L_P) plus the length of the body 18 (L_B) of frac ball 12 in the direction of flow must be greater than the inner diameter of the well 14 (ID_W), and is expressed in the following equation:

Length of Projection (L_P)+Length of Body in the Direction Flow (L_B)>Inner Diameter of Well (ID_W)

Because the total length of the frac ball 12 as described above, including the projection and the body, is greater that the inner diameter of the well 14, the projection 20 prohibits the frac ball 12 from rotating in the well bore 14 during placement, thus maintaining orientation of the frac ball 20 in substantially the same orientation as when the frac ball is inserted into the well 14. When the body 18 of the frac ball 12 is a sphere or torus, the length of the body is the same as the diameter of the sphere or torus. However, when the body 18 of the frac ball 12 is a polyhedra, the length of the body is determined by the distance between the two outermost vertices of the body as positioned downhole in the direction of flow. For a cylinder or cone, the length of the body 18 is the height of the cylinder or cone.

The projection 20 may be formed integrally with the body 18, as shown in FIG. 10, or it may be later molded onto or added to the body 18. The projection 20 may be solid, hollow, or porous and may be formed of any material suitable for use downhole in well 14, including plastics, wood, composites, metals, water soluble substances, substances soluble in cement, substances soluble in drilling fluid and combinations of the foregoing. It will be appreciated that the body 18 may be comprised of any materials suitable to the particular pressures, temperatures, fluids and other conditions at the well 14 where in use. The projection 20 generally has a density ranging from about 8 lbs/ft³(0.128 g/cm³) to about 500 lbs/ft³(7.85 g/cm³).

In one embodiment of the invention, the projection 20 is comprised of a material that dissolves or breaks during pump back operations or when it otherwise is desired to remove the frac ball 12 from the well 14. During the pump back process, in which the frac ball 12 will move through progressively larger seats 16 up the well 14 toward the surface, the projection 20 does not hinder the removal of the projection 20 from the well 14 when it breaks or dissolves from the body 18. To that end, the projection 20 may further comprise serrations or perforations 26 as shown in FIG. 11, or comprise a plurality of narrower sections 28 that facilitate breakage, as shown in FIG. 12. Additionally, the projection 20 may comprise a chamfer 30 that is susceptible to breakage where it is countersunk below the exterior surface 32 of body 18, as shown in FIG. 12.

It will be appreciated that frac ball 12 further may comprise a plurality of projections, an exemplar of which is shown FIG. 13, which depicts rods 20A, 20B and 20C extending in multiple directions. Multiple projections in more than one direction potentially may hinder the ability of the frac ball 12 to pass through seats 16 during pump back operations. Accordingly, if the distance between the extreme of any two plural projections, 20A and 20B, 20B and 20C or 20A and 20C, extending in multiple directions does not exceed the diameter of the body 18, a plurality of projections may be used to provide greater stability to the frac ball 12 when in motion.

The projection 20 may be solid or it may comprise a porous substance to make the projection lighter in weight and more maneuverable downhole. Additionally, a porous projection 20 may be more susceptible to breakage or dissolution in a soluble substance thereby facilitating removal from the wellbore 14. It now will be appreciated that the projection 20 alters the geometry of the frac ball 12 and orients the body 18 with respect to the z axis of the well 14.

The frac ball 12 of the present invention also or alternatively may comprise a magnet 40, shown in FIG. 14, which could be molded into the frac ball or attached to the exterior of the frac ball. A corresponding magnet 42 in the sealing seat 16 creates a magnetic attraction with the magnet 40 in the frac ball 12, thus orienting the frac ball in the desired position on the seat.

With continuing reference to FIGS. 4 through 13, the present invention also comprises a method of substantially sealing a zone in a subterranean formation 10, the subterranean formation comprising at least one seat 16. The method comprises the step of orienting a barrier or frac ball 12 comprising a body 18 and a projection 20 connectable with the body so that the frac ball is substantially sealingly receivable in the seat 16. In graduated fracturing ball drop systems, the frac ball travels through progressively smaller sealing seats until it reaches its intended depth, where it mates with the appropriately sized seat and activates a sealing mechanism such as a sliding sleeve, thus effectively sealing off a subterranean zone for treatment or other purposes. The frac ball may be oriented with the projection 20 pointing generally toward the top side of the formation 10. The frac ball 12 also may be oriented so that the projection 20 points generally toward the underside of the formation 10. The method may further comprise the step of removing the frac ball 12 from the well 14. Removal may be accomplished by severing the projection 20 from the body 18 or breaking the projection into parts to facilitate removal of the ball from the subterranean formation. Removal of frac ball 12 also may be facilitated by dissolving the projection 20.

Turning again to FIG. 14, the present invention also comprises a method of substantially sealing a zone in a subterranean formation 10, the subterranean formation comprising at least one seat 16, wherein the method comprises the step of orienting a barrier or frac ball 12 comprising a body and a magnet so that the barrier is substantially sealingly receivable in the seat. The sealing seat 16 also comprises a magnet. During installation of the frac ball 12 in the subterranean formation 10, and as the frac ball 12 nears the metal sealing seat 16, a magnetic force attracts the body 18 of the frac ball 12 to the magnet 42 in the seat, thus orienting the ball in the desired position downhole to withstand compressive forces.

It now will be appreciated that the subject invention provides an effective apparatus and means of controlling the orientation of a frac ball and particularly a composite frac ball on the sealing seat of a well. The present invention overcomes difficulties associated with controlling orientation of composite frac balls and provides a method of use.

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what has been believed to be preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected with a generic disclosure. Changes may be made in the combination and arrangement of the various parts, elements, steps and procedures described herein without departing from the spirit and scope of the invention as defined in the following claims.