Patent Application
20140251594
In a staged fracturing operation, multiple zones of a formation need to be isolated sequentially for treatment. To achieve this, operators install a fracturing assembly down the wellbore, which typically has a top liner packer, open hole packers isolating the wellbore into zones, various sliding sleeves, and a wellbore isolation valve. When the zones do not need to be closed after opening, operators may use single shot sliding sleeves for the fracturing treatment. These types of sleeves are usually ball-actuated and lock open once actuated. Another type of sleeve is also ball-actuated, but can be shifted closed after opening.
Initially, operators run the fracturing assembly in the wellbore with all of the sliding sleeves closed and with the wellbore isolation valve open. Operators then deploy a setting ball to close the wellbore isolation valve. This seals off the tubing string of the assembly so the packers can be hydraulically set. At this point, operators rig up fracturing surface equipment and pump fluid down the wellbore to open a pressure actuated sleeve so a first zone can be treated.
As the operation continues, operates drop successively larger balls down the tubing string and pump fluid to treat the separate zones in stages. When a dropped ball meets its matching seat in a sliding sleeve, the pumped fluid forced against the seated ball shifts the sleeve open. In turn, the seated ball diverts the pumped fluid into the adjacent zone and prevents the fluid from passing to lower zones. By dropping successively increasing sized balls to actuate corresponding sleeves, operators can accurately treat each zone up the wellbore.
When initially run downhole, the inner sleeve 30 positions in the housing 20 in a closed state. A breakable retainer 38 initially holds the inner sleeve 30 toward the upper sub 22, and a locking ring or dog 36 on the sleeve 30 fits into an annular slot within the housing 20. Outer seals on the inner sleeve 30 engage the housing 20's inner wall above and below the flow ports 26 to seal them off.
The inner sleeve 30 defines a bore 35 having a seat 40 fixed therein. When an appropriately sized ball lands on the seat 40, the sliding sleeve 10 can be opened when tubing pressure is applied against the seated ball 40 to move the inner sleeve 30 open. To open the sliding sleeve 10 in a fracturing operation once the appropriate amount of proppant has been pumped into a lower formation's zone, for example, operators drop an appropriately sized ball B downhole and pump the ball B until it reaches the landing seat 40 disposed in the inner sleeve 30.
Once the ball B is seated, built up pressure forces against the inner sleeve 30 in the housing 20, shearing the breakable retainer 38 and freeing the lock ring or dog 36 from the housing's annular slot so the inner sleeve 30 can slide downward. As it slides, the inner sleeve 30 uncovers the flow ports 26 so flow can be diverted to the surrounding formation. The shear values required to open the sliding sleeves 10 can range generally from 1,000 to 4,000 psi (6.9 to 27.6 MPa).
Once the sleeve 10 is open, operators can then pump proppant at high pressure down the tubing string to the open sleeve 10. The proppant and high pressure fluid flows out of the open flow ports 26 as the seated ball B prevents fluid and proppant from communicating further down the tubing string. The pressures used in the fracturing operation can reach as high as 15,000-psi.
After the fracturing job, the well is typically flowed clean, and the ball B is floated to the surface. Then, the ball seat 40 (and the ball B if remaining) is milled out. The ball seat 40 can be constructed from cast iron to facilitate milling, and the ball B can be composed of aluminum or a non-metallic material, such as a composite. Once milling is complete, the inner sleeve 30 can be closed or opened with a standard “B” shifting tool on the tool profiles 32 and 34 in the inner sleeve 30 so the sliding sleeve 10 can then function like any conventional sliding sleeve shifting with a “B” tool. The ability to selectively open and close the sliding sleeve 10 enables operators to isolate the particular section of the assembly.
When aluminum balls B are used, more sliding sleeves 10 can be used downhole for the various stages because the aluminum balls B can have a close tolerance relative to the inner diameter for the seats 40. For example, forty different increments can be used for sliding sleeves 10 having solid seats 40 used to engage aluminum balls B. However, an aluminum ball B engaged in a seat 40 can be significantly deformed when high pressure is applied against it. Any variations in pressuring up and down that allow the aluminum ball B to seat and to then float the ball B may alter the shape of the ball B, compromising its seating ability or its ability to float to the surface after use.
Additionally, aluminum balls B if left downhole can be particularly difficult to mill out of the sliding sleeve 10 due to their tendency of rotating during the milling operation. For example,
One problem with using aluminum balls B can be the long mill up times required per zone. For instance, milling just one frac stage when a solid aluminum ball is used can take up to an hour. During mill up, larger aluminum balls B push through the seats as a large quarter segment S of the ball. This segment S travels down to the next seat 40 and contacts the next ball B, as shown in
Using non-metal balls may avoid the problem of longer milling times because the non-metal balls break apart easier during mill up. Yet, as noted previously, these non-metal balls may not hold the desired operating pressures and may not provide as many stages as can be obtained with the minimized aluminum ball and seat engagement.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
A plug is used for engaging in a downhole seat and is milled out after use. The plug has a body with an outer surface and an interior. The plug can be a ball, and the body can be spherical. Additionally, the plug's body can be composed of a metallic material, such as aluminum.
The body has a plurality of holes formed therein. In particular, the holes extend from at least one common vertex point on the outer surface of the body and extend at angles partially into the interior of the body. The at least one common vertex point can be at least one tap hole defined in the outer surface of the body, and the plurality of holes can be a plurality of angled holes formed at an angle into the interior from the at least one tap hole. At least a portion of the holes can have a filler material disposed therein.
In one implementation, common vertex points disposed on opposing sides of the body can be used. In this case, the holes include a first set of angled holes formed at an angle into the interior from one of the common vertex points on one of the opposing sides. Additionally, the holes include a second set of angled holes formed at an angle into the interior from the other of the common vertex points on the other of the opposing sides. The first and second sets of angled holes can be offset from one another.
Manufacturing the plug involves forming the body with the outer surface and the interior. The holes are formed in the body by extending the holes from at least one common vertex point on the outer surface of the body and extending the holes at angles partially into the interior of the body.
To extend the holes from the at least one common vertex point on the outer surface of the body, the method can involve forming at least one tap hole in the outer surface of the body and forming a plurality of angled holes formed at an angle into the interior from the at least one tap hole. In one implementation, tap holes can be formed on opposing sides of the body. In this way, a first set of angled holes can be formed at an angle into the interior from one of the tap holes, and a second set of angled holes can be formed at an angle into the interior from the other tap hole. These first and second sets of angled holes can be offset from one another.
The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.
Fracture balls composed of metal, and particularly aluminum, have material removed from the ball's interior. The removal of the material can be done in various ways. In general, holes can drilled to a specified depth in the ball, but the holes do not create a through-hole in the ball, as this would compromise the sealing ability of the ball. Instead, the holes create voids (not through-holes) and allow the ball to stay intact during fracturing operations. The holes in the ball also allow the ball to break up easier during milling operations.
As noted in the background of the present disclosure, mill out of a solid metal (aluminum) ball may cause a large segment of the ball to push through the seat before being fully milled. The partially milled segment then travels to the next ball/seat below it. The segment and ball then tend spin when the mill reaches them, which increases the mill up times. However, the disclosed ball having the partial hole(s) defined therein tends to break up into smaller pieces that allow the mill to grab them when it travels to the lower seat. Although the partial hole(s) may be beneficial for milling, the ball must still be capable of properly seating on the ball seat and preventing leakage and must be able to withstand the increased pressures of the fracture operations.
Voids, spaces, or holes are defined in the body 102 to facilitate milling of the ball 100 when disposed in a ball seat of a tool, such as a sliding sleeve. Because the ball 100 has the purposes of sealingly engaging the ball seat in the sliding sleeve, the ball 100 preferably is configured to maintain or produce a sufficient seal with the ball seat when seated therein. Therefore, the voids, spaces, or holes do not pass entirely through the body 102. Instead, as shown in
Drilled off at angles from the tap hole 110 are a plurality of angled holes 112—four such angled holes 112 are shown in the ball 100 of
All the same, the tap hole 110 can be left unplugged and act as a suitable void. Alternatively, the tap hole 110 can plugged with material, such as epoxy, resin, solder, plastic, rubber, the same metal material as the body 102, other type of metal than the body 102, or the like. The angled holes 112 can even be filled at least partially with filler material that can be readily milled.
Each angled hole 112 can be angled at about 45-degrees from the centerline of the tap hole 110, and the angled holes 112 may be offset at about 90-degrees from one another around the tap hole 110. As with the tap hole 110, the angled holes 112 may extend to less than the mid-section of the ball's body 102, but this may vary for a given implementation. The ball 100 in
For some exemplary dimensions for the ball 100 having a diameter of about 3-in., the tap hole 110 can be about ⅜-in. wide and can extend about ⅓ of the diameter (e.g., about 1-in.) of the body 102. The angled holes can be about ¼-in. wide and can extend about 1.75-in. in length. Other sized balls 100 would have other dimensions, of course. In any event, balls 100 having a diameter of about 2-in. or greater would be best suited for the types of holes disclosed herein simply because balls with smaller diameters are already easier to mill.
As before, the tap holes 110a-b can primarily provide common vertices Va-Vb from which the opposing angled holes 112a-b can be formed so that multiple tap points do not need to be made in the ball's surface 104. The ball 100 in
In other differences illustrated, the angled holes 112 can be drilled at a shallower angle from the tap hole 110. Additionally, the ends of the angled holes 112 can extend beyond the midpoint of the ball's body 102. Thus, the angled holes 112 extend nearly to the opposing side of the ball's body 102.
As can be seen from the various arrangements of holes in
In general, the ball 100 (if solid) would have about 10× the structural strength required to achieve its purposes downhole. Removing material with the holes 110/112 could reduce the structural strength to perhaps 2 to 3 times what is needed. In any event, a given ball 100 with the holes 110/112 is preferably capable of withstanding at least 7,000-psi, and more preferably 10,000-psi, without collapsing on itself. Of course, the different diameters of balls and seats used and the associated materials will govern any such variables.
As shown in
Finally, as shown in
Although these chunks C may pass to the next ball and seat downhole, their irregular shape and fragmented nature makes them easier to mill further when the mill 50 reaches the next ball and seat arrangement downhole. The chunks C and any exposed holes on the other ball create points of friction that can facilitate milling. As an example of what possible chunks C may be left of a metallic ball after milling and passing through a seat,
Again, some of the ball remains as chunks during milling that can then pass through the seat before the mill 50 actually grinds the entire ball and seat during milling operations. Rather than producing a quarter segment of the ball B as encountered with a solid metal ball when milled, the voided ball 100 produces less uniform and less substantial chunks. One chunk is shown as being flat in shape and as defining remnants of the various holes (112) formed in the ball's body 102. This makes this chunk more susceptible to further breaking and grinding during further milling stages. Other chunks are smaller pieces removed from the voided ball 100 during milling.
As an alternative to a spherical ball having holes to facilitate milling, a metallic ball 200 as shown in
Manufacture of the balls 100/200 disclosed herein can be performed in a number of ways depending on the type of material used. For example, the balls 110/200 can be formed by casting, machining, drilling, and a combination thereof. Any holes 110/112 in the balls 110 can be formed by casting, machining, drilling, and a combination thereof. These and other such manufacturing details will be appreciated by one skilled in the art having the benefit of the present disclosure.
The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. It will be appreciated with the benefit of the present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can be utilized, either alone or in combination, with any other described feature, in any other embodiment or aspect of the disclosed subject matter.
In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.
This application claims the benefit of the U.S. Prov. Appl. 61/774,729, filed 8 Mar. 2013, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61774729 | Mar 2013 | US |
