Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B33/00—Sealing or packing boreholes or wells
  • E21B33/10—Sealing or packing boreholes or wells in the borehole
  • E21B33/13—Methods or devices for cementing, for plugging holes, crevices or the like
  • E21B33/138—Plastering the borehole wall; Injecting into the formation

Definitions

• This invention relates to ball sealers for plugging perforations in a pipe and more particularly to ball sealers which will selectively bridge across perforations that are receiving a disproportionately large amount of well treatment fluid being injected into a wellbore.
• the flow of a disproportionately large amount of treating material through one or a few perforations in the casing may be attributable to the higher permeability of the formation adjacent to those perforations. If the treating fluid may be easily pumped through one or a few perforations, it is often impossible to pump enough fluid into the well to build up sufficient hydrostatic pressur in the wellbore to force fluid or treating material through the perforations communicating with less permeable formations or generally impermeable sections of the earth formations.
• One solution to the above-recited problem involves temporarily plugging at least some of the perforations communicating with the permeable sections of earth formations during the injection of treatment materials so that the hydrostatic pressure in the wellbore is permitted to develop to the extent that treatment fluids and materials are forced into the less permeable sections of the earth formation through other perforations which remain open.
• Ball sealers have been developed in the industry for accomplishing this selective plugging process to solve this fluid loss problem.
• ball sealing elements are usually made of rubber or of a hard-core material surrounded by a resilient outer covering.
• the balls are inserted into the well as fluid is pumped through the perforations.
• the balls are carried along by the flowing stream of fluid and seat against the casing perforations through which the preponderance of fluid passes, i.e., those perforations communicating with permeable sections of earth formation.
• the ball sealer element plugs the perforation and is held in place by the pressure against it of the fluid in the casing to thereby prevent passage of the fluid in the casing through the plugged perforations.
• Such ball sealers are shown in U.S. Patent No. 2,754,910, issued July 17, 1956, to Derrick; U.S. Patent No.
• the present invention relates to a ball sealer for sealing off perforations in a wellbore wherein the sealers are comprised of an impermeable outer deformable shell defining a central core portion, which core portion is filled with nondeformable particulate matter that is sized to 'flow into the shape assumed by the deformable outer shell.
• Figure 1 is a diagrammatic sectional view of a perforated oil well with ball sealers being pumped into the well;
• Figure 2 is a partially cut away view of a ball sealer;
• Figure 3 shows a cross-sectional view of a ball sealer engaging a perforation in a well casing
• Figure 4 shows a perspective view of a prior art ball sealer positioned in an irregular perforation in a casing wall.
• a casing 12 is run to the bottom of the well and cemented as at 14 around the outside at least to a distance above the producing formations 16, as shown.
• the casing 12 and the cement 14 are then perforated by any one of various means to provide a fluid communication channel between the producing formations and the interior of the casing. If the well does not come into production, it is then a common practice to treat the well by some process which will open up the producing formation to allow a ready passage of formation fluids into the wellbore. Such remedial treatment operations may also be employed in an older producing well when the production therefrom has diminished to an uneconomical level.
• such treatment processes typically include acidizing, hydraulic fracturing, or the like which involve pumping a treating material down the casing and into the producing formation through the perforations 18 which extend through the casing and into the earth formations.
• Exceedingly high pressures are sometimes used in such treatment operations with pressures of 10,000 psi not being unusual. It is well recognized that under these conditions, treating materials will preferentially flow through certain of the perforation more readily than through others. It is apparent then that only that part of the formation which is receiving this preferential flow is being subjected to the intended treatment. It, therefore, becomes desirable to selectively close off those perforations through which the highly disproportionate share of materials are flowing so that the treatment materials will be forced to act on the formation adjacent to the other perforations.
• balls 22 are introduced into the treating materials which are being pumped into the casing 12.
• the wellbore shown in Figure 1 utilizes a tubing string 24 which is suspended in the wellbore from the surface and having an open lower end thereof terminating near the producing formations 16.
• a packer 26 is provided about the outside of the tubing 24 and is -arranged to seal the annular space between the tubing 24 and the casing 12, above the perforations 18 in the casing.
• the treating material is pumped down and out the end of the tubing 24 and through the perforations 18 in the casing and cement into the adjacent formation.
• the balls 22 are introduced through a lubricator 28 at the surface and are moved down the tubing 24 with the treating materials which are entering the tubing through the pipe 32.
• the balls are forced selectively to engage the perforations such as at 34 through which the major portion of treating materials are flowing, leaving open those perforations through which the treating materials are not being injected. These balls seal off the perforations just so long as the pressure within the tubing and casing is greater than the pressure in the formation. When the pressure is reduced at the surface, the ball sealers will be released from engagement with the perforations. Thereafter, flow will be established through all of the perforations.
• the plugs are carried by the fluid stream to the particular perforation through which the treating material is entering the formation and the sealing action can be determined readily by the increase in pressure at the well head.
• the plugs can be admitted or introduced as desired and move readily with the material traveling at a rate such that it can be easily determined when they will arrive at the sealing position and the plugs can be admitted one or two or as many at a time as needed according to the pressure rise and fall within the casing.
• the pressure will constantly rise until such time as the material is injected into the formation. At that time, the pressure will drop, indicating that the formation has broken down, and at this time, plugs will be introduced into the fluid stream to plug the perforations opposite the existing permeability.
• FIG. 4 Such a prior art sealer is shown in Figure 4 wherein a typical ball sealer 10 is shown projecting into an irregular perforation 11 in a casing 12. It is readily seen that a substantial amount of fluid flow leakage might be possible around a sealing configuration as that shown in Figure 4, such as through the space 13 formed between the ball 10 and irregular opening 11.
• An outer shell 42 is constructed of a durable yet flexible and impermeable material such as rubber to form a deformable bladder around a core portion 44 which is filled with particulate matter 46, as shown in. Figure 2.
• This particulate matter 46 may be comprised of beads of material such as nylon or other substantially nondeformable material.
• a graded material works well in that the individual particles tend to move readily relative to one another as not to assume a fixed relationship.
• Spherical beads would provide the ultimate mobility to the particulate core material with the size of the particles or beads being determinative of the degree of mobility. Basically, the smaller the bead, the more fluid like the core will be. On the other hand, very fine core particles will tend not to form a bridge across the opening of the perforation but rather will tend to flow through the opening.
• a compromise between the desired functional qualities of fluidity and ability to bridge will determine the size of core particle.
• the span of the perforation opening will provide the primary parameter in determining such particle size.
• a rule of thumb which is used when designing treatment processes, for example, a gravel pack, is to size the particulate matter to be greater than one-sixth the diameter of the perforation to be closed by the bridging effect of gravel.
• the particles are sized to be less than one-sixth .the size of the perforation to ensure that the particles will flow through the perforation.
• Standard new perforations are nominally about 10 mm in diameter. When corrosion and wear are taken into account, 12 mm would be a good estimate for the size of old perforations.
• the particulate material will tend to consolidate into a bridge more easily than in loose condition and thus could be somewhat smaller in size than the rule of thumb, one-sixth perforation diameter used for gravel packs or the like.
• a size range of 1.5 to 3 mm or 6 to 12 mesh would be an appropriate size for the particulate matter 46 ( Figure 2) within the shell 42.
• the outside diameter of the shell would be sized to be approximately 22 mm or more when the perforations are about 12 mm.
• the core of the ball sealers further comprises a temporary binder material such as a wax or similar material to bind the beads or particles together while the cover is formed about the core.
• the temporary binder material preferably has a melting temperature lower than the operating temperatures downhole but high enough to form a workable solid at about room temperature. Thereafter, the temporary binder material forms a liquid in the interstices of the beads or particles within the cover. The melted binder may form a lubricant causing the beads to easily slide relative to one another.
• the liquid binder would be more capable of resisting the ⁇ downhole compressive forces than air or other gaseous media and would therefore prevent the cover from deforming into the interstices of the beads.
• the weight of the ball sealers, or more particularly, the specific gravity of the ball sealers is an important design criterion since the ball sealers are intended to flow with the well treatment fluid. If the ball sealers were too heavy or too light, they would be less inclined to flow with the fluid and plug the perforations. Therefore, the ball sealers should have approximately the same density as the well treatment fluid so as to be relative neutrally buoyant therein (i.e. the ball sealers should not necessarily float to the top or sink to the bottom) . However, under some circumstances it may be preferable to provide the ball sealers with a small positive buoyan ⁇ y (float relative to the fluid) and in other situations to provide ball sealers with a negative buoyancy (sink in the fluid) .
• the particles and the temporary binder which form the core are particularly selected so as to form ball sealers having a predetermined specific gravity. It is conventional in the art to provide sealers having a variety of specific gravities generally in the range of 1.0 to 1.3 to accommodate the variety of well treatment fluids that may be used. Based on such figures, the ball sealers of the preferred embodiment having a diameter of approximately 7/8 inch would weigh generally between 0.2 and 0.26 ounces. Turning now to an operation utilizing the ball sealers of the present invention, if it was determined that certain formations were taking treating materials in disproportion to the total flow volume, the sealers would be introduced into the flow stream through the lubri- cator 28 at the surface.
• the particles 46 making up the core of the ball sealer 22 will migrate or flow with the changing shape of the outer rubber casing 42 as it spreads over and into the perforation under the influence of hydraulic forces acting on the ball 22.
• the shell 42 assumes a round shape, the thickness and nature of material making up the shell 2 is such that the shape of the sealer may readily change under the applied forces of the hydraulic system in which it is operating.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Geology (AREA)
• Mining & Mineral Resources (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Pipe Accessories (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=23875833

Family Applications (1)

Country Status (5)

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• 1991
  • 1991-01-07 EP EP19910902904 patent/EP0465623A4/en not_active Withdrawn
  • 1991-01-07 AU AU71453/91A patent/AU7145391A/en not_active Abandoned
  • 1991-01-07 CA CA002049974A patent/CA2049974A1/en not_active Abandoned
  • 1991-01-07 WO PCT/US1991/000225 patent/WO1991011587A1/en not_active Application Discontinuation
  • 1991-09-27 NO NO91913809A patent/NO913809L/no unknown

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