BACKGROUND OF THE INVENTION
The present invention relates generally to the control of tools used downhole in a subterranean wellbore and more particularly provides, in various illustratively depicted embodiments thereof, specially designed annular plug seat assemblies having circumferentially overlapping seat segment joints.
A common practice for controlling various types of tools downhole, such as for example, sliding sleeve valves, is to use pressurized fluid to flow a ball (or other type of plug structure) down the wellbore to land on a generally annular seat structure operatively associated with the particular tool. When the ball lands on the seat, it blocks fluid from flowing in a downhole direction through the seat, thereby creating a pressure drop across the seat that may be utilized to create a control event such as shifting a sliding sleeve valve.
Many seat configurations have been previously proposed, the most simplistic of which being a solid ring with an inner diameter smaller than the ball's diameter. Seats capable of expanding to let the ball pass therethrough have also been previously proposed. These seats incorporated a collet-like structure, or radial dogs contained in an axially movable sleeve, and when engaged by a ball were slidable to a further downhole position at which diametrical expansion of the collet or dogs was permitted to allow the ball to pass through the seat. Such previously proposed seat designs often proved to be problematic since they have inherent gaps that could be infiltrated by sand, mud, cement or grit often present in the well. These gaps between the circumferential seat segments could be present when balls were not passing through the seats, thus enabling the infiltrating contaminants to cause system seize-up.
Another previously proposed diametrically expandable annular seat design, illustrated and described in copending U.S. patent application Ser. No. 13/887,779 filed May 6, 2013 and assigned to the assignee of the present invention, does not incorporate a collet-like structure, or have radially sliding dogs contained within an axially moveable sleeve. Instead, a circumferentially segmented annular seat rests against a conical shoulder rigidly affixed to the tool. The seat is diametrically compressed from the opposing side with a conically engaging sleeve that is biased against the seat via a spring or by fluid pressure. In this seat design there are no gaps for contamination to penetrate during periods when balls are not passing through the seat. This is especially important when hydraulically fracturing a well since cement and proppant would certainly penetrate such gaps. Conveniently, when hydraulically fracturing a well with a sliding sleeve ball drop system, the practice is typically to remove the slurry while pumping down a ball to create a pad of clean water around the ball. Consequently, momentary gaps while the ball passes do not see proppant, mud, or cement. This practice is primarily used to reduce the chance of an undesirable screen-out condition.
While this last-mentioned annular plug seat design has been found to be generally satisfactory for its intended purposes, and superior in performance to seats with collet or dog configurations, it has also been found that a single plane axially extending interface provided between each circumferentially adjacent seat segment pair may, in some instances such as when the balls are pumped downhole at higher speeds, cause the seat to malfunction. It is desirable to pump balls at a fast rate since pumping down too slowly can cause the proppant to fall out of suspension with the associated fluid. When balls are pumped down at too great a speed, the simple single plane interfaces between each circumferentially adjacent seat segment pair may allow individual seat segments to be washed into the bore in front of the ball. Such seat segment washout (in which a segment is axially separated from the balance of the seat) typically causes complete collapse of the seat and/or seizure of the non-washed out segments in a manner preventing balls from passing through the remainder of the seat.
As can be seen from the foregoing, a need exists for an improved annular downhole tool plug seat structure that eliminates or at least substantially alleviates the above-mentioned problems, limitations and disadvantages of previously proposed seat designs as generally described above. It is to this need that the present invention is primarily directed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view through a representative downhole tool operatively incorporating therein a specially designed circumferentially segmented plug seat assembly embodying principles of the present invention;
FIG. 2 is an enlarged scale perspective view of the plug seat assembly in a diametrically compressed orientation;
FIG. 3 is an enlarged scale perspective view of the plug seat assembly in a diametrically expanded orientation;
FIG. 4 is an enlarged scale perspective view of a first alternative embodiment of the plug seat assembly in a diametrically compressed orientation;
FIG. 5 is an enlarged scale perspective view of a second alternative embodiment of the plug seat assembly in a diametrically expanded orientation;
FIG. 6 is a schematic, radially inwardly directed, partially phantomed elevational view of portions of a circumferentially adjacent segment pair of a third alternative embodiment of the plug seat assembly in a diametrically compressed orientation;
FIG. 7 is a schematic, radially inwardly directed, partially phantomed elevational view of portions of a circumferentially adjacent segment pair of a fourth alternative embodiment of the plug seat assembly in a diametrically compressed orientation; and
FIG. 8 is a cross-sectional view through one of the FIG. 7 plug seat assembly segments taken along line 8-8 of FIG. 7.
DETAILED DESCRIPTION
Cross-sectionally illustrated in FIG. 1 is a representative tubular downhole tool 10 centered about a longitudinal axis 12 and coaxially received in a tubing section 13 of a wellbore string. Tool 10 which, by way of non-limiting example, is a sliding sleeve valve, operatively and coaxially supports therein a first embodiment 14 of a specially designed annular, diametrically expandable plug seat assembly embodying principles of the present invention. Referring now additionally to FIGS. 2 and 3, plug seat assembly 14 includes a series of arcuate rigid peripheral circumferential segments 16 (representatively, but not by way of limitation, six in number) illustratively formed from a suitable metal material. At facing ends thereof each circumferentially adjacent pair of segments 16 circumferentially overlap each other at multifaceted juncture areas 18 (see FIGS. 1 and 2) which serve to prevent, by means of a rigid blocking action between each given segment 16 and the two segments 16 between which it is interposed, the axial separation in either direction of the given segment 16 from the balance of the plug seat 14.
In the plug seat embodiment 14 shown in FIGS. 1-3, the segment ends that form each of the multifaceted juncture areas 18 have zig-zagged or “puzzle cut” configurations such that the two ends slidably interlock as may be best seen by comparing FIGS. 2 and 3. Plug seat 14, as later described herein, when operatively supported in the tool 10, is expandable from a FIG. 2 diametrically compressed orientation initially blocking a pre-selected plug ball (not shown) from passing therethrough, to a FIG. 3 diametrically expanded orientation in which the interior diameter of the plug seat 14 is increased (by fluid pressure on a plug ball landing on the seat) to an extent permitting the plug ball to pass through the plug seat 14. In each of these two diametric orientations of the plug seat 14, the segments 16 circumferentially overlap one another in a manner preventing any of the segments 16 from being completely dislodged axially from the rest of the seat segments 16.
As can best be seen in FIG. 3, each of the rigid segments 16 has one end on which a generally V-shaped projection 20 is formed and has angled facet portions 22, and an opposite end on which a generally V-shaped recess 24 is formed and has angled facet portions 26. Each projection 20 is complementarily receivable in one of the recesses 24 in a manner such that with the plug seat 14 in its FIG. 2 diametrically compressed orientation, the facet pairs 22 of each segment 16 are slidingly and sealingly engaged with the facet pairs 26 of an adjacent segment 16. As illustrated in FIGS. 1 and 2, the plug seat 14, when in its diametrically compressed orientation has conically tapered, oppositely sloped annular peripheral surfaces 28,30 respectively disposed on its top and bottom sides.
As cross-sectionally depicted in FIG. 1, the expandable plug seat 14 is coaxially sandwiched between (1) the conically tapered end surface 32 of a rigid tubular member 34 coaxially anchored, as by a threaded connection 36, to a tubular sleeve 38 slidably received in the wellbore string tubular section 13, and (2) the conically tapered end surface 40 of an axially shiftable tubing component 42 telescoped within the tubular sleeve 38. The tapered top annular peripheral surface 28 of the expandable seat 14 is slidably and complementarily engaged by the conically tapered end surface 40, and the tapered bottom annular peripheral surface 30 of the expandable seat 14 is slidably and complementarily engaged by the conically tapered end surface 32. For purposes later described herein, an annular pocket area 44 is formed within the interior of the tool 10 and outwardly circumscribes the expandable seat 14.
Between the tubular members 38 and 42 another annular pocket area 46 is formed within the tool 10 and receives an annular compression spring structure 48 that forcibly bears against axially opposing annular portions 50,52 of the tubular members 42,38 and resiliently biases the tubular member 42 in a downhole direction 54. This causes the tapered peripheral surface areas 28,30 of the expandable seat 14 to be forcibly wedged between the tapered tubular member end surfaces 40,32 to thereby cammingly create around the periphery of the seat 14 a radially inwardly directed force that yieldingly urges the seat 14 toward its diametrically compressed orientation shown in FIGS. 1 and 2.
When a plug ball (not shown), or another type of plug member, is downwardly pumped through the interior of the tool 10 and complementarily engages the concavely curved inner side surface 56 of the expandable seat 14, a fluid pressure drop is created axially across the seat 14. This pressure drop, in turn, generates a radially outwardly directed force 58 around the periphery of the seat 14 that cammingly drives the tubing component 42 upwardly away from its FIG. 1 position, against the biasing force of the spring 48, and diametrically expands the seat 14 into the pocket area 44 to the FIG. 3 diametrically expanded orientation of the seat 14, thereby permitting the ball to be pumped downwardly through the expanded seat 14
Upon passage of the ball through the expanded seat 14, the spring 48 downwardly returns the upwardly displaced tubing component 42 to its FIG. 1 position to thereby cammingly drive the diametrically expanded seat 14 back to its diametrically compressed orientation shown in FIGS. 1 and 2. As described above, the circumferentially overlapping of the individual seat segments 16 prevents axial separation of any of the segments 16 from the balance of the overall seat assembly 14. When the seat 14 is returned to its diametrically compressed orientation, the multifaceted segment ends re-seal at their juncture areas 18.
A first alternate embodiment 14a of the previously described expandable plug seat 14 is perspectively illustrated in its diametrically compressed orientation in FIG. 4. To facilitate the comparison of the plug seats 14 and 14a, components in the seat 14a similar to those in the seat 14 have been given identical reference numerals to which the subscript “a” have been appended. Expandable plug seat 14a is identical to seat 14 with the exception that in the seat 14a layers of a suitable elastomeric material 60 are bonded within the multifaceted juncture areas 18a of the seat 14a. Each elastomeric material layer 60 may be bonded to both of its two associated facing seat segment ends, or to only one of them. The use of the elastomeric material 60 desirably eliminates the necessity to precisely machine the segment end facets to achieve a fluid tight seal at the segment juncture areas when the seat assembly 14a is in its diametrically compressed orientation.
A second alternate embodiment 14b of the previously described expandable plug seat 14 is perspectively illustrated in FIG. 5 in a diametrically expanded orientation which, for illustrative purposes, is of a larger diameter than would be momentarily created by a plug ball operatively passing therethrough in the tool 10. To facilitate the comparison of the plug seats 14 and 14b, components in the seat 14 similar to those in the seat 14 have been given identical reference numerals to which the subscript “a” have been appended. Unlike the segments 16 of seat 14, the seat segments 16b of the expandable plug seat 14b do not have zig-zagged multi-faceted “puzzle cut” opposite ends to create circumferential overlapping between adjacent segment ends. Instead, the opposite ends 62,64 of the main body of each seat segment 16b lie in single, axially extending planes, with circularly cross-sectioned pin portions 66 projecting outwardly from the ends 62 and being complementarily and slidably receivable in corresponding circularly cross-sectioned holes 68 extending inwardly into the ends 64. This permits the seat 14b to expand and contract between its diametrically compressed and expanded positions with the pin/hole surface interfaces all the while maintaining a circumferential segment overlap that prevents axial separation of any one of the segments 16b from the balance of the overall expandable seat 14b.
As can be seen in FIG. 5, while the segment pin portions 66 prevent axial separation of any seat segment 16b from the balance of the seat 14b, under certain operational conditions the seat segments may exhibit a tendency to slightly “rock” around the pin axes. If such an event is anticipated and considered undesirable, such segment rocking may be easily eliminated, as shown in a portion of an alternate embodiment 14c of the expandable seat 14b schematically depicted in FIG. 6. To facilitate the comparison of the plug seats 14c and 14b, components in the seat 14c similar to those in the seat 14b have been given identical reference numerals to which the subscript “c” have been appended.
Schematically shown in FIG. 6 are portions of two adjacent seat segments 16c in an abutting relationship that they assume with the seat 14c in its diametrically compressed orientation. Instead of utilizing a single pin on one end of each seat segment, in the seat 14c each planar segment end 62c has two pins 66c projecting therefrom and slidably received in two holes 68c projecting into the end 64c of an adjacent segment 62c, thereby preventing rocking of any of the segments 16c relative to the balance of the seat 14c.
A schematically depicted portion of an alternate embodiment 14d of the two segment pin seat embodiment 14c is shown in FIG. 7. To facilitate the comparison of the plug seats 14d and 14c, components in the seat 14d similar to those in the seat 14c have been given identical reference numerals to which the subscript “d” have been appended. In the seat embodiment 14d, the seat 14c circular holes 66c and holes 68c are replaced with a single, non-circularly cross-sectioned segment end pin 70 (representatively of a rectangular cross-section as shown in FIG. 8) which is slidably received in a complementarily configured segment end hole 72 to prevent undesired seat segment rocking.
The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.
Patent Grant
9506322
