US20110303418A1

US20110303418A1 - Method and apparatus for reducing impact force in a ball-seat assembly

Info

Publication number: US20110303418A1
Application number: US12/813,853
Authority: US
Inventors: Mohan L. Soni; Gaurav Agrawal
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 2010-06-11
Filing date: 2010-06-11
Publication date: 2011-12-15

Abstract

A method of restricting fluid flow includes: releasing a ball into a fluid conduit and receiving the ball in a ball receiving element disposed at the fluid conduit and at least partially restricting fluid flow; and at least partially reflecting one or more pressure waves resulting from an impact between the ball and the ball receiving element by a reflective boundary disposed in the fluid conduit.

Description

BACKGROUND

In the drilling and completion industry and for example in hydrocarbon exploration and recovery operations, a variety of components and tools are lowered into a borehole for various operations such as production operations, for example. Some downhole tools utilize ball-seat assemblies to act as a valve or actuator. Ball-seat assemblies are used with, for example, hydraulic disconnects, circulating subs and inflatable packers.
Actuation of a ball-seat assembly generally includes releasing a ball or other plug from a releasing mechanism and allowing the ball to drop onto the ball seat and restrict a fluid conduit. The impact between the ball and the ball seat can produce pressure waves, which can cause wear and/or damage to the ball-seat assembly and other components. For example, initial impact is generally the most severe and is compounded by the suction pressure on the ball seat due to an outgoing expansion wave downstream of the seating area.

SUMMARY

A method of restricting fluid flow includes: releasing a ball into a fluid conduit and receiving the ball in a ball receiving element disposed at the fluid conduit and at least partially restricting fluid flow; and at least partially reflecting one or more pressure waves resulting from an impact between the ball and the ball receiving element by a reflective boundary disposed in the fluid conduit.
An apparatus for restricting fluid flow includes: a ball receiving element disposed in a fluid conduit and configured to receive a ball that has been advanced through the fluid conduit and at least partially restrict fluid flow; and a reflective boundary disposed in the fluid conduit at least partially reflecting one or more pressure waves resulting from an impact between the ball and the ball receiving element.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 is a cross-sectional view of a subterranean well drilling, well logging, evaluation, exploration and/or production system

FIG. 2 is a flow diagram depicting a method of restricting fluid flow in a conduit;

FIG. 3 is a cross-sectional view of an embodiment of a ball-seat assembly including a first and a second fluid injected into a conduit of the ball-seat assembly; and

FIG. 4 is a cross-sectional view of an embodiment of a ball-seat assembly including a first and second fluid injected into a conduit of the ball-seat assembly.

DETAILED DESCRIPTION

The apparatuses, systems and methods described herein provide for controlling downhole fluid flow and mitigating pressure waves caused by actuation of a ball-seat assembly. A downhole actuator assembly includes a conduit having a longitudinal component to guide a ball released into the conduit to a ball receiving element such as a ball seat. A reflective boundary disposed in the conduit at least partially reflects one or more pressure waves resulting from an impact between the ball and the ball receiving element. One embodiment of a method of reducing pressure waves includes pumping a first downhole fluid into the conduit, followed by pumping a second downhole fluid that has a characteristic that is different than the characteristic of the first downhole fluid, which creates a reflective boundary from the interface between the first and second fluids that acts to reflect incident pressure waves created by an impact between the ball and the ball receiving element. The reflected pressure waves destructively interfere with the incident pressure waves to reduce the amplitude of the incident pressure waves and reduce wear on downhole components such as the ball and the ball seat. Examples of such characteristics include density, viscosity, polarity, and chemical and/or physical differences causing the fluids to resist mixing or combining.
Referring to FIG. 1, an exemplary embodiment of a subterranean well drilling, well logging, evaluation, exploration and/or production system 10 includes a borehole string 12 such as a production string that is shown disposed in a borehole 14 that penetrates at least one earth formation 16 during a subterranean operation. The borehole string may include any type of carrier, such as a downhole sub or wireline. A tool 18, such as a ball seat sub, includes a housing 20 having a longitudinal bore or fluid conduit 22. A ball-seat assembly includes a ball receiving element such as a ball seat 24 included in the conduit 22 to retain a ball 26 that is released into the conduit 14. In one embodiment, the ball 26 is a spherical metal or plastic plug, although “ball” may refer to any type of moveable or droppable plugging element, such as a drop plug, and may take any desired shape or size. Actuation of the ball seat assembly includes releasing the ball into the fluid conduit 14, for example by dropping the ball 18 into and/or pumping the ball 18 through the fluid conduit 14 from a surface or downhole location. The ball 18 falls and/or is advanced by downhole fluid toward the ball seat 16 and is seated on the ball seat 16 to restrict fluid flow through the conduit 14.
The ball seat 24 may be an annular component connected to the conduit 22, or any other device or configuration providing a restriction in the diameter or cross-sectional area of the conduit 22 sufficient to prevent the ball 26 from passing therethrough. For example, the ball seat 24 may be attached to the inner surface of the conduit 22 or include a reduced diameter portion of the conduit 22.
In one embodiment, the tool 18 is configured to be in fluid communication with at least one pumping device 28 that is configured to introduce into and/or advance a fluid through the borehole string 12 and the fluid conduit 22. In one embodiment, a processor or other device, such as a surface processing unit 30 is in operable communication with the pumping device 28 and/or the tool 18 to communicate with and control operation of the pumping device 28 and/or the ball-seat assembly. The downhole tool 10 is not limited to that described herein. The borehole string 12 and/or the tool 18 may include any tool, carrier or component that includes a ball seat assembly. In addition, the tool 18 is not limited to components configured for downhole use.
FIG. 2 illustrates a method 40 of restricting fluid flow in a component. The method includes, for example, actuating a valve or packer in a downhole assembly. The method 40 includes one or more stages 41-43. Although the method is described in conjunction with the system 10 and the downhole tool 18, the method can be utilized in conjunction with any device or system (configured for downhole or surface use) that utilizes a ball-seat assembly.
In the first stage 41, in one embodiment, the downhole tool 18 is deployed downhole and advanced along the borehole 14 to a desired position, such as via a borehole string 12 or a wireline. In the second stage 42, a first downhole fluid having a first characteristic such as a first density is injected, pumped or otherwise introduced into the fluid conduit 22. In the third stage 43, a second downhole fluid having a second characteristic such as a second density is introduced into the fluid conduit 22 at a time proximate to or otherwise dependent on a time of release of the ball 18 or an anticipated time of actuation of the ball-seat assembly. In the fourth stage 44, the ball-seat assembly is actuated by releasing the ball 26 into the conduit 22, for example by dropping the ball 18 into the conduit 14 and/or pumping the ball 18 through the conduit 14. The ball 18 advances through the conduit 14 and impacts the ball seat 16. The different characteristics of the first and second downhole fluids create an interface or boundary that acts to reflect one or more incident pressure waves resulting from an impact between the ball 26 and the ball seat 24. The pressure waves destructively interfere with the incident pressure waves and dissipate the pressure waves to reduce the severity and duration of loads created by the pressure waves. This dissipation may also reduce the suction pressure on the ball-seat assembly due to the outgoing expansion wave downstream of the seating area. The different characteristics may be any characteristics sufficient to create a reflective boundary between the first and second fluids. For example, the fluids may have different densities or viscosities. In one embodiment, the fluids may have different chemical polarities. For example, the first fluid may be a generally polar fluid such as a water-based fluid and the second fluid may be a generally non-polar fluid such as an oil-based fluid.
An embodiment of the method 40 is described in conjunction with FIG. 3, which shows an embodiment of a ball-seat assembly 50. In this embodiment, a first downhole fluid 52 is pumped into the fluid conduit 22 via, for example, the borehole string 12. The ball 26 is released upon actuation of the ball-seat assembly 50, and at a selected time after ball release, a second downhole fluid 54 is pumped into the conduit 22. The first fluid 52 pumped ahead of the ball 26 has a first density ‘A’ that is different than a second density ‘B’ of the second fluid 54 pumped right after the ball. In one embodiment, the density A is greater than the density B, although the density A may be less than the density B in other embodiments. Various types of fluids may be used, such as water having a density of 8.3 pounds per gallon (ppg) and various drilling muds, such as water based drilling fluids having various densities (e.g., 16.5 ppg), and oil based muds which may have various densities ranging from, for example, 8-18 ppg.
The interface between fluids having the densities A and B results in a boundary 56 that provides a surface for the reflection of the incident pressure wave(s). Reflected pressure waves reflected from the boundary 56 at least partially cancel out the original pressure wave(s) created at the time of impact and reduces the net pressure resulting from impact.
The pumping of the second fluid 54 is initiated at a time so that the boundary 56 advances with the ball 26 at a selected distance from the ball 26. In this way, the distance of the boundary 56 from the ball 26 and the ball seat 24 at the time of impact can be controlled. For example, the injection or pumping of the second fluid 54 is triggered prior to or in anticipation of ball-seat actuation so that the boundary 56 is formed upstream and/or downstream of the ball 26. The pumping of the second fluid 54 may be initiated so that the boundary 56 is proximate to the ball 26, so that the boundary 56 is located proximate to the ball seat 24 at time of impact to rapidly dissipate the incident pressure wave(s).
Another embodiment of the method 40 is described in conjunction with FIG. 4. In this embodiment, the first fluid 52 of density ‘A’ is pumped first, followed by the second fluid 54 of density ‘B’ which carries the ball. Density B may be, for example, greater than density A. In one embodiment, the second fluid 54 is injected at a time relative to ball-seat assembly actuation so that the ball 26 is carried by the second fluid and the boundary 56 is downhole of the ball 26 but still close to the ball 26. Upon impact, the boundary 56 is downhole of the ball 26 and the incident pressure wave is a negative expansion waveform but the dense fluid reflection is a positive or compression wave that will tend to cancel the tensile or negative wave. Thus the amount of force on the ball 26 will be less because the pulling force from below will be cancelled out by the reflected waves. In one embodiment, the first fluid 52 of density ‘A’ (or another fluid having a density different than the density ‘B’) is additionally injected or pumped following the second fluid 54. The density difference between A and B thus creates a density contrast, i.e., a boundary 56, relative to the ball at both upstream and downstream locations. Impact of the ball 26 upon the ball seat 24 creates a pressure wave in both the upstream and downstream directions, which are at least partially reflected and dissipated by the boundaries 56. Thus the net pressure on the ball-seat assembly 50 resulting from the impact is reduced by successively pumping different density fluids.
The apparatuses and methods described herein provide various advantages over existing processing methods and devices. Wear on the ball-seat assembly, which is a function of force over distance and time, can be reduced by reducing the force of the ball of the seat through the reduction in amplitude of the pressure wave(s). This reduction directly reduces the probability of ball-seat damage and conversely improves its reliability. The reduction of pressure waves affecting the ball-seat assembly can enable the use of a wider range of construction materials and reduce the cost and complexity of ball-seat design, for example by reducing the need for relatively complex ball seat designs to reduce impact. In addition, the apparatuses and methods can allow for the ball seat to have a larger inner diameter due to the reduced contact stress.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention.

Claims

1. A method of restricting fluid flow, comprising:

releasing a ball into a fluid conduit and receiving the ball in a ball receiving element disposed at the fluid conduit and at least partially restricting fluid flow; and

at least partially reflecting one or more pressure waves resulting from an impact between the ball and the ball receiving element by a reflective boundary disposed in the fluid conduit.

2. The method of claim 1, wherein the fluid conduit includes a first fluid having a first characteristic.

3. The method of claim 2, further comprising injecting a second fluid into the fluid conduit, the second fluid having a second characteristic different than the first characteristic and configured to form an interface between the first fluid and the second fluid, the interface forming the reflective boundary.

4. The method of claim 3, wherein the characteristic is selected from at least one of a polarity, a viscosity, a chemical composition and a physical composition.

5. The method of claim 3, wherein the first characteristic is a first density and the second characteristic is a second density.

6. The method of claim 1, wherein at least partially reflecting includes generating at least one reflected wave that destructively interferes with the one or more pressure waves.

7. The method of claim 3, wherein the second fluid is injected at a time that is dependent on a release time of the ball so that the interface is located at a selected distance relative to the ball at impact.

8. The method of claim 3, wherein the second fluid is injected at a time that is dependent on a release time of the ball so that the interface is located at least one of upstream and downstream of the ball receiving element at impact.

9. The method of claim 7, further comprising injecting an additional fluid after the second fluid, the additional fluid having a characteristic different than the second characteristic so that the interface is located both upstream and downstream of the ball receiving element at impact.

10. The method of claim 1, further comprising disposing a carrier including the actuator assembly in a borehole.

11. An apparatus for restricting fluid flow, comprising:

a ball receiving element disposed in a fluid conduit and configured to receive a ball that has been advanced through the fluid conduit and at least partially restrict fluid flow; and

a reflective boundary disposed in the fluid conduit at least partially reflecting one or more pressure waves resulting from an impact between the ball and the ball receiving element.

12. The apparatus of claim 11, wherein the boundary at least partially reflects one or more pressure waves resulting from an impact between the ball and the ball receiving element, and generates at least one reflected pressure wave that destructively interferes with the one or more pressure waves.

13. The apparatus of claim 11, wherein the fluid conduit is configured to receive a first fluid having a first characteristic.

14. The apparatus of claim 13, wherein the fluid conduit is configured to receive a second fluid, the second fluid having a second characteristic different than the first characteristic and configured to form an interface between the first fluid and the second fluid, the interface forming the reflective boundary.

15. The apparatus of claim 14, wherein the characteristic is selected from at least one of a polarity, a viscosity, a chemical composition and a physical composition.

16. The apparatus of claim 14, wherein the first characteristic is a first density and the second characteristic is a second density.

17. The apparatus of claim 14, further comprising a processor configured to inject the second fluid at a time that is dependent on a release time of the ball so that the interface is located at a selected distance relative to the ball at impact.

18. The apparatus of claim 14, further comprising a processor configured to inject the second fluid at a time that is dependent on a release time of the ball so that the interface is located at least one of upstream and downstream of the ball receiving element at impact.

19. The apparatus of claim 18, wherein the processor is configured to inject an additional fluid after the second fluid, the additional fluid having a characteristic different than the second characteristic so that the interface is located both upstream and downstream of the ball receiving element at impact.

20. The apparatus of claim 11, further comprising a carrier including the ball receiving element and the fluid conduit, the carrier configured to be disposed in a borehole.