This application is the U.S. national phase of International Application No. PCT/EP2012/062980 filed 4 Jul. 2012 which designated the U.S. and claims priority to EP Patent Application No. 11173224.4 filed 8 Jul. 2011, the entire contents of each of which are hereby incorporated by reference.
The present invention relates to a downhole hydraulic pump for providing fluid pressure during downhole operations.
Downhole tools using fluid as a driving force are increasingly used during downhole operations, especially for driving operational tools and/or for engagement of the borehole wall or borehole casing. Hydraulic power for these fluid working units is provided by downhole hydraulic pumps. Due to downhole conditions, such hydraulic pumps are limited in many ways and still have to perform efficiently to save time and money during downhole operations. The physical extent of the pumps is limited due to spatial restrictions in the borehole, the power supplied is limited, typically because a wireline reaching from the surface is limited due to large voltage drops over long distances, or if downhole batteries are used, the spatial restriction again becomes the limiting factor. Furthermore, hydraulic pumps must be efficient to provide sufficient driving force and speed for the downhole fluid working units since this limits downhole operating times, which in turn reduces cost. Also, downhole pumps must be durable since breakdowns are even more critical to operating times as all maintenance and repair must be done on the surface, necessitating a complete retraction of the downhole tools from the boreholes. Known hydraulic pumps comprise a plurality of piston chambers of cyclically varying volume in which the displacement of fluid through the piston chambers is provided by a rotating cam lobe forcing the pistons to move in a cyclic manner. However, such hydraulic pumps are often not sufficiently efficient to provide the power needed downhole and may furthermore suffer from wear on the moving parts.
It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved hydraulic pump providing more fluid power during downhole operations than prior art pumps.
The above objects, together with numerous other objects, advantages, and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by a downhole hydraulic pump for providing fluid pressure during downhole operations, comprising:
The downhole hydraulic pump according to the present invention may further comprise a plurality of pistons, piston housings, inlet and outlet valves and piston springs.
Further, the piston may be moved in a first direction in the piston housing by the cam lobe and in a second direction by the piston spring.
Moreover, the pump housing may have an inlet in fluid communication with the inlet of the piston housing.
Said pump housing may have an outlet in fluid communication with the outlet of the piston housing.
In an embodiment, a clearance distance between a piston side wall and an inner wall of the piston housing may be below ten micrometers in width.
The downhole hydraulic pump as described above may furthermore comprise a bearing arranged between the cam shaft and the cam ends of the plurality of pistons.
This bearing may be a needle bearing.
In addition, the downhole hydraulic pump according to the present invention may comprise a set of pistons, piston housings, inlet valves, outlet valves and piston springs arranged in the pump housing and having a mutual distance along the longitudinal axis.
Furthermore, the downhole hydraulic pump according to the present invention may comprise a plurality of pistons, a plurality of piston housings, a plurality of inlet valves, a plurality of outlet valves and a plurality of piston springs, and a set may comprise one piston, one piston housing, one inlet valve, one outlet valve and one piston spring. The downhole hydraulic pump may further comprise a plurality of sets arranged in the pump housing and having a mutual distance along the longitudinal axis, each set being arranged symmetrically in an asterisk shape, substantially radially away from the longitudinal spin axis.
In one embodiment, the pump may further comprise twelve pistons arranged in four layers of three pistons, each at four different positions along the longitudinal spin axis, each layer of three pistons being arranged radially with an asterisk angle of 120 degrees between them, and each layer being shifted in a shift angle of 30 degrees so that all twelve pistons have a unique radial position with a 30 degree separation to the radially neighbouring pistons.
Additionally, the inlet and outlet valves may be one-way valves, such as ball valves.
Moreover, a plurality of balls of the ball valves may be made from a ceramic material.
The downhole hydraulic pump according to the present invention may further comprise an accumulating unit in fluid connection with the plurality of outlet valves.
Further, the cam lobe having two cam lobe end faces may further comprise at least one hollow section providing a fluid communication channel between said cam lobe end faces.
The pump housing as described above having two pump housing end faces may further comprise at least one hollow section providing a fluid communication channel between said pump housing end faces.
In addition, the downhole hydraulic pump according to the present invention may further comprise a filter unit arranged upstream of, and in fluid connection with, the plurality of inlet valves.
Also, the downhole hydraulic pump according to present invention may further comprise a plurality of indentations in the pump housing, the indentations having a form corresponding to a neighbouring movable part comprised within the pump housing, such as the piston, the piston housing and/or the piston spring.
Additionally, the piston housing as described above may be rotatably suspended in the pump housing.
A maximum internal hydraulic pressure of the pump may preferably exceed 100 bars, more preferably exceed 300 bars, and even more preferably exceed 600 bars.
Moreover, the piston housings may be rotatably attached to the pump housing in a first end of the piston housing by arranging the inlet valve in a cylindrical groove in the pump housing, suspended by a rotatable ring-shaped seal in one end, and attaching an opposite end of the inlet valve in the piston housing and mutadis mutandis in a second end of the piston housing by arranging the outlet valve in a cylindrical groove in the pump housing and suspended by a rotatable ring-shaped seal in one end and attaching an opposite end of the outlet valve in the piston housing.
Further, the cam shaft may be suspended in the pump housing by a set of cam shaft bearings.
The piston spring as described above may be arranged circumscribing the piston.
Also, the piston spring may be arranged circumscribing the piston and partially circumscribing the piston housing.
The spring may be arranged inside the piston housing.
In addition, the piston may be hollow.
A maximum rotational speed of the pump may preferably exceed 4000 rpm, more preferably exceed 6000 rpm, and even more preferably exceed 8000 rpm.
Furthermore, the piston spring as described above may have a spring constant preferably exceeding 2000 N/m, more preferably exceeding 3000 N/m, and even more preferably exceeding 4000 N/m.
Finally, the downhole hydraulic pump according to the present invention may further comprise a plurality of grooves along an outer surface of the pump housing.
In an embodiment of the invention, the inlet and outlet valves may be fixedly connected with the pump housing or the piston housings.
Moreover, the inlet and outlet valves may be non-fixedly connected with the pump housing or the piston housings.
In addition, the inlet and outlet valves may be fixedly connected with the pump housing, and the inlet and outlet valves may be non-fixedly connected with the piston housings.
Furthermore, the inlet and outlet valves may be fixedly connected with the pump housing or the piston housings by a fixed ring-shaped valve seal.
Additionally, the inlet and outlet valves may be non-fixedly connected with the pump housing or the piston housings by non-fixed ring-shaped valve seal.
Finally, the inlet and/or outlet valves may be integral parts of the pump housing or the piston housings.
The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which
All the figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.
The term “fluid power” will be used throughout the text to define power transmitted by a controlled circulation of pressurised fluid to a motor or another unit that converts the fluid power into a mechanical output capable of doing work on a load. Fluid power is therefore a function of pressure as well as velocity of the hydraulic fluid.
The piston housing 7 has an inlet valve 8 arranged in an inlet of the piston housing 7 and an outlet valve 9 arranged in an outlet of the piston housing. The piston arranged in the piston housing encloses a volume. The valves are one-way valves, and when the cam lobe 5 moves the piston 6 into the piston housing 7, the volume is decreased and fluid in the volume is forced out through the outlet valve 9 into outlet channels 30. Further, when the cam moves away from the piston housing 7, the spring ensures that the piston 6 follows the cam shaft 3 in the opposite direction and that the volume increases, thereby letting fluid in through the inlet valve 8. In this way, a rotational force of the cam shaft is transferred to pumping fluid into outlet channels 30 to activate an operational tool connected to the pump.
The piston housing is rotatably connected to the pump housing, enabling rotation of the piston housing 7 around a piston housing rotation axis A2 parallel to the longitudinal spin axis A1 of the shaft 4. The hydraulic pump 1 may further comprise an accumulating unit 13 in fluid connection with the plurality of outlet valves 9 for collecting the pressurised fluid generated in all the piston housings 7. The hydraulic pump 1 may further comprise a filter 76 arranged upstream of, and in fluid connection with, the plurality of inlet valves 8 for filtering any unwanted coarse particles from the hydraulic fluid entering the piston housing 7. A filter 76 significantly reduces wear of the hydraulic pump 1.
The piston housings are arranged rotatably connected to the pump housing, as shown in
By using inlet and outlet valves 8, 9 and connecting them rotatably to the piston housing 7 and pump housing by valve seals 11 such as O-rings, both the rotation of the piston housings and the sealing of the inside of the piston housings 7 and the inlet and outlet valves 8, 9 are provided, and additional bearings are avoided.
The piston may alternatively be constituted by a more conventional piston and rod arrangement known from the art, which may lower a mass of the piston and may lower the resistance of the piston during movement in the piston housing.
The pump housing has two pump housing end faces and at least one hollow section providing a fluid communication channel between the pump housing end faces. The pump housing may include a plurality of indentations, the indentations having a form corresponding to a neighboring movable part comprised within the pump housing, such as the piston, the piston housing, and/or the piston spring. The pump housing may further comprise a plurality of grooves along an outer surface of the pump housing.
The hydraulic pump 1 pumps the hydraulic fluid towards other downhole tools requiring hydraulic power during downhole operations. Typically, the hydraulic fluid is led back to the hydraulic pump 1 in a closed loop since operational time would otherwise be very limited since normally only small volumes of hydraulic oil are available in a downhole tool string. In such a closed loop of the hydraulic fluid, the hydraulic fluid is advantageously led back through an interior 37 of the pump due to the special limitations downhole. In this way, the interior 37 of the pump acts as a hydraulic fluid tank. Having this type of arrangement, however, requires that the flow through the interior 37 is not limited so that the pump is limited by the hydraulic flow back to the inlet valves 8. Therefore, the interior 37 has to be optimised for flow conditions through the pump housing. An additional advantage of such an arrangement is the constant lubrication of the moving parts inside the interior 37 by the hydraulic fluid.
The function of the piston spring 10 is to oppose the force from the cam trying to push the piston towards the piston housing. The piston springs 10 may, for convenience, be arranged alternatively to the embodiments shown in the figures, such as inside the piston or inside the piston housing and still fulfill the purpose of the spring.
The inlet and outlet valves 8, 9 may be one-way ball valves. To improve the responsiveness of the ball valves, very light balls 8a may preferably be used. Especially during very high rotational speeds, the weight of the balls might become a limiting factor to the efficiency of the pump since the balls cannot be moved quickly enough within the ball valve. For the purpose of having a very light ball, ceramic materials are very useful due to the combination of weight and durability. Since ceramic materials are very durable and very light, such materials may advantageously be used for the ball valves.
The cam shaft 3 is connected to a rotational shaft 42 of a motor and suspended in a set of cam shaft bearings 39, such as ball bearings, to ensure a smooth rotation of the cam shaft 3 with little friction.
The cam shaft bearings 39 may be locked with locking rings (not shown), again to provide more open space in the interior 37 to minimise the resistance of the backflow of hydraulic fluid through the pump housing.
The compactness of the hydraulic pump 1 with overlapping sets of piston housings allows for a very short pump shaft in the longitudinal direction. A short pump shaft, i.e. a short length of the cam and cam shaft, provides the ability to have a thin and strong shaft, since again, the dimension is essential for the versatility in downhole equipment. Furthermore, the symmetry of the pump provides a constant force on the cam shaft.
Thus, in order to decrease the wear of moving parts in the downhole hydraulic pump, the inlet and outlet valves may be fixedly connected with either the pump housing or the piston housings, but not necessarily both. By only non-fixedly connecting the inlet and outlet valves with the pump housing or the piston housings in one end of the inlet and outlet valves, the piston housing may still be rotated around an axis, and the wear of the pump may be decreased in the fixed end of the inlet and outlet valves.
The inlet and outlet valves may be fixedly connected to the pump housing or the piston housings by application of e.g. a fixed ring-shaped valve seal or a welded connection. In some embodiments of the invention, the inlet and outlet valves may be an integral part of the pump housing or piston housing.
Although the invention has been described in the above in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.
Number | Date | Country | Kind |
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11173224 | Jul 2011 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2012/062980 | 7/4/2012 | WO | 00 | 1/6/2014 |
Publishing Document | Publishing Date | Country | Kind |
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WO2013/007566 | 1/17/2013 | WO | A |
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Number | Date | Country | |
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20140127046 A1 | May 2014 | US |