US 20020070015 A1
A down-hole tool hydraulic force intensifier is disclosed utilizing an intensifier piston having an enlarged fluid facing top surface for receipt of hydraulic pressure thereon to force such intensifier piston against the activating structure of the down-hole tool to effectively increase the hydraulic force thereon.
1. A hydraulic force intensifier for use with a down-hole tool having activating means and a bottom, comprising:
an intensifier piston having an enlarged fluid facing top surface, a narrow piston body and a relatively narrower throughbore defined longitudinally therein;
a sub having an aperture defined therein for slideable receipt of said piston body and enlarged fluid facing top surface of said intensifier piston, said sub including means for attachment to said down-hole tool at the bottom thereof;
means for attachment to a source of hydraulic pressured fluid; and
said enlarged fluid facing top surface adapted to receive said hydraulic fluid pressure over a wider surface area than would otherwise be received by said tool for increasing the force of said intensifier piston body on said activating means of said tool.
2. The force intensifier of
a plurality of said intensifier pistons aligned in series to receive said hydraulic fluid pressure against the enlarged fluid facing top surfaces of each of said intensifier pistons for effectively increasing the pressure on said activating means of said down-hole tool.
 1. Field of the Invention
 The invention relates to apparatus for increasing the force used to activate a hydraulically operated down-hole tool and more particularly relates to an apparatus that increases such force without having to increase the pressure of the hydraulic fluid.
 2. History of the Prior Art
 It is conventional practice when drilling well boreholes to create such boreholes in steps. Initially a large diameter borehole is drilled to a particular depth. In order to structurally support the borehole and prevent collapse, the borehole is lined with standard steel tubing known as a casing which is cemented in place. Subsequent sections of the borehole are then drilled with a smaller drill bit attached to a work string which can be lowered through the previously installed casing. As a consequence each section of the borehole and casing will have a smaller diameter to that which is above it.
 Expandable reaming tools are commonly used during the above described procedure and typically comprise a plurality of expandable arms which can move between a closed and an open position. The expandable reaming tool is passed through the in-place casing with the arms in a closed position behind a pilot drill bit which drills the section of the borehole. After passing through the casing the expandable reaming tool or underreamer can be opened in order to enlarge the borehole below the casing.
 The blades of extendible reaming tools are commonly extended by a piston which is activated by a hydraulic force created by the pressure of fluid passing through the work string. However it will be appreciated that boreholes often extend several thousands of meters in depth, and it is therefore difficult when working at such depths to effectively control the pressure of the hydraulic fluid and hence the driving force on the tool. Fluid pressure is typically determined by pumping apparatus at the surface, and such pressure may progressively diminish due to various back pressures at remote distances down-hole. It is also not always desirable, or possible, to use high pressure in certain conditions, for example, in deep, low-pressure wells.
 It is an object of the present invention to provide a tool design of the type which is activated by a hydraulic force, the level of which force is adjustable without the requirement of an increase in fluid pressure beyond a predetermined maximum.
 It is therefore an object of this invention to provide an apparatus for increasing the hydraulic force applied to a hydraulically operated down-hole tool for any given hydraulic fluid pressure.
 According to the present invention there is provided a hydraulically operated down-hole tool, the tool having one or more pistons in series wherein each piston provides a fluid facing surface on which hydraulic fluid operates wherein the combined fluid facing surface of the plurality of pistons increases the surface area on which the hydraulic fluid operates such that the force exerted by the hydraulic fluid on the down-hole tool is proportionately greater than the force which would be produced by any given hydraulic pressure alone.
 In a preferred embodiment the down-hole tool of this invention can be an expandable reaming tool having a plurality of reaming members which are movable between a first closed position and a second expanded position. The reaming members can be moved from a first closed position to the second expanded position by virtue of the movement of a first activating piston. Such activating piston is usually biased against movement under hydraulic force by a mechanical spring. The spring can serve to return the activating piston to its original position when fluid pressure is reduced. The expandable reamer tool can have a plurality of restricted exit flow ports.
 An intensifier piston or pistons in series of this invention is used in conjunction with such activating piston. Such intensifier piston(s) is adapted to be acted upon by fluid pressure and is mechanically linked with the activating piston so as to transmit such force onto the activating piston. A plurality of intensifier pistons in series can be used to increase the total surface area upon which pressurized fluid is able to act, thereby increasing the total activating force.
 The activating and intensifier piston(s) can have an internal collinear axial bore. The intensifier piston can have a plurality of fluid outlet ports which allow fluid to pass from the internal bore of the intensifier piston into a recess located substantially behind the activator piston. The intensifier piston can be slidably mounted in a sub wherein the sub is connectable to a work string.
FIG. 1 illustrates a longitudinal cross-sectional view of the intensifier piston of this invention.
FIG. 2 illustrates a longitudinal cross-sectional view of an intensifier sub without an associated intensifier piston therein.
FIG. 3 illustrates a longitudinal cross-sectional view of the intensifier piston of FIG. 1 in position within the sub of FIG. 2.
FIG. 4 illustrates a longitudinal cross-sectional view of a down-hole tool having an activator piston and intensifier piston therein.
FIG. 5 illustrates the down-hole tool of FIG. 4 after hydraulic pressure has been applied thereto.
FIG. 6 illustrates a longitudinal cross-sectional view of an alternate embodiment of this invention having two intensifier pistons arranged in series.
FIG. 1 illustrates intensifier piston 1 having narrow piston body 2 and relatively narrower throughbore 3. Piston body 2 has a plurality of drilled holes 4 defined therein. Piston body 2 is designed such that it provides an enlarged fluid facing top surface 5 on which hydraulic fluid can operate to create a downward force. Body 2 also has an O-ring seal 6.
FIG. 2 illustrates an intensifier sub 7 having O-ring 8 and sub through holes 9 which act as pressure equalizers. Sub 7 further has a threaded end connection 10 which enables sub 7 to be mounted on a work string or the like. The relationship between sub 7 of FIG. 2 and intensifier piston 1 of FIG. 1 is shown in more detail in FIG. 3. In FIG. 3 it can be seen that intensifier piston 1 is slidably fitted within sub 7 and can move relative to sub 7 under the influence of hydraulic fluid operating on fluid facing top surface 5.
 In FIGS. 4 and 5 a down-hole tool 11 is depicted. Shown in FIGS. 4 and 5 is an extendible reaming tool otherwise known as an underreamer although it should be noted that any hydraulically operated tool can be used and still fall within the scope of the present invention. Tool 11 comprises body 12 and plurality of blades 13 which can be moved from a first closed position, as seen in FIG. 4, to a second open position, as seen in FIG. 5 where the blades have been rotated 90 degrees. In use, the tool is run into a well borehole with blades 13 entering first. Body 12 contains activating piston 14 which is movable and which acts to extend blades 13. The main body of the tool also comprises an activating member 15 which is located next to coiled spring 16.
 To activate the underreamer, hydraulic fluid is pumped through the work string which, although not shown, is well known in the prior art. Positioned directly behind activating piston 14, and in series therewith, is intensifier piston 17 and associated piston sub 18. Intensifier piston 17 increases the force exerted on activating piston 14 by hydraulic fluid by virtue of increasing the surface area on which the hydraulic fluid operates. Specifically, the hydraulic fluid pumped from the surface of the well borehole will push on fluid facing surfaces 19 and 20 and cause intensifier piston 17 to move relative to piston sub 18 from the position illustrated in FIG. 4 to the position illustrated in FIG. 5. In turn, activating member 15 and coiled spring 16 are compressed, moving activating piston 14 in a downward direction and moving blades 13 from the closed position shown in FIG. 4 to the open position shown in FIG. 5 where the blades are shown rotated 90 degrees.
 Intensifier piston 17 also has defined therein intensifier piston bore 21. It will be appreciated that fluid will be able to pass through intensifier piston bore 21 through intensifier piston 17. This fluid flow passes through intensifier piston bore 21 until it reaches drilled piston holes 4, as shown in FIG. 1. The fluid can pass through these holes 4 into a recess 22 which is located next to, and directly above, activating member 15. This fluid acts to create further force on activating member 15 of activating piston 14 which in turn helps compress coiled spring 16 and move activating piston 14 downwards. Activating piston 14 also has an activating piston bore 23 defined therein.
 It will be appreciated that the advantage of the present invention lies in the fact that the inclusion of the intensifier piston increases the surface area on which the hydraulic fluid within the work string can push, and consequently creates an increase in force on the activating piston which activates the hydraulic tool. This increased force can be achieved without increasing the pressure at which the fluid is pumped down-hole.
FIG. 5 illustrates the piston when activated. Fluid can escape by means of a plurality of restricted exit ports, not shown, on the underreamer tool itself, or by being forced back through activating piston 23 of activating piston 14 via back pressure and exiting into recess 22.
FIG. 6 illustrates an alternate embodiment of the present invention wherein a double intensifier piston is used. Sub 24 is elongated such that a first and second intensifier piston 25 and 26 are positioned in series and are aligned with one another directly behind an activator piston which is not shown. It will be appreciated that the inclusion of two intensifier pistons will further increase the surface area on which the hydraulic fluid can operate, namely on fluid facing surfaces 27, 28, 29 and 30. Although only one or two intensifier pistons are illustrated, it is within the scope of this invention that a series of such intensifier pistons can be incorporated into a tool.
 Although the present invention has been described with reference to particular embodiments, it will be apparent to those skilled in the art that variations and modifications can be substituted therefor without departing from the principles and spirit of the invention.