The present invention relates to a downhole power system, a constant flow downhole assembly and a related method for providing fluid into a turbine of the downhole power system.
Fluid fed down coiled tubing is used for driving a variety of tools or drilling bits. When driving a tool, a wireline is not always suitable or capable of providing adequate power for powering the tool, and thus the pressurised fluid fed down the tubing is used. The tubing may be connected to a turbine for converting the energy from the pressurised fluid into a mechanical energy; however, tests have shown that the turbines are very quickly destroyed. Thus, in order for such coiled tubing system to be reusable, substantial repair work often has to be performed.
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 downhole system in which pressurised fluid fed down a tubing is used for powering a tool downhole consuming a substantial amount of power while being reusable operation after operation, hence eliminating the need to perform substantial repair work.
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 power system comprising:
a tubing string comprising a pressurised fluid,
a turbine for converting energy from the pressurised fluid into rotation of a shaft,
a tool powered by the turbine,
wherein a constant flow downhole assembly is arranged between the tubing string and the turbine for providing a substantially constant flow of the pressurised fluid to the turbine,
wherein the constant flow downhole assembly has an assembly axis and comprises:
a body comprising a main bore having a bore inlet and at least one bore outlet,
a hollow piston having a piston inlet and a piston outlet, said hollow piston being arranged in the main bore, and
a spring arranged in the main bore, said spring being compressed upon movement of the piston in a first direction, and
wherein the bore inlet is in fluid communication with the piston inlet and the piston inlet is smaller than the bore inlet so as to force the piston to move in the first direction.
The downhole power system as described above may further comprise a generator arranged between the turbine and the tool, the generator comprising a rotor and a stator and the rotor being connected with the shaft.
In one embodiment, a gearing unit may be arranged between the shaft and the rotor.
Moreover, the bore inlet may be in fluid communication with the piston inlet.
Further, the piston may have a piston end wall surrounding the piston inlet, the piston inlet being opposite the bore inlet.
In addition, the piston inlet may be smaller than the bore inlet so as to force the piston to move in the first direction.
In an embodiment, the piston may have a piston wall adapted to partly cover the bore outlet when the piston moves in the first direction for reducing the flow of fluid into the bore outlet.
The piston wall may uncover the bore outlet when the piston moves in a second direction opposite the first direction for increasing the flow of fluid into the bore outlet.
Additionally, the piston outlet may be arranged in the piston wall.
Also, the piston outlet may be elongated and extend along the assembly axis.
Furthermore, the piston may have a plurality of piston outlets arranged circumferentially around the piston wall.
Moreover, the bore outlet may be arranged radially in relation to the assembly axis.
In an embodiment, the main bore may comprise a plurality of bore outlets.
The bore outlets may be arranged circumferentially around the main bore.
In addition, the piston may have a first end opposite a second end, the first end having the piston outlet, and the spring may abut the first end of the piston.
Further, the spring may be arranged partly within the piston and may abut a piston end wall in which the piston inlet is arranged.
Also, the main bore may comprise first openings arranged upstream of the piston to allow pressurised fluid to flow in a bypass channel out through second openings and into apertures arranged in the piston wall.
Changeable flow restrictors may be arranged in the first openings.
Moreover, the constant flow downhole assembly may comprise a sleeve covering the flow restrictors.
In an embodiment, the sleeve may form part of the bypass channel.
Additionally, the sleeve may be displaceable or disconnectable for changing the flow restrictors.
The main bore may be closed in an end opposite the inlet by an end wall, and the spring may be arranged between the end wall and the piston.
Furthermore, the constant flow downhole assembly may be a self-regulating valve.
Also, the constant flow downhole assembly may be adapted to regulate a flow of fluid in the range of 0.5-5 barrels/min.
Further, the spring may be adapted to absorb a pressure of up to 700 bar (10,000 PSI).
Moreover, the flow restrictors may be nozzles.
In addition, the tool may be a driving unit, such as a downhole tractor.
The tool may be a sensor tool, a stroker tool, a key tool, a cutting tool, a neutron tool, a laser diagnostic tool, a laser cutting tool, a casing collar locator, an acoustic tool, a pulse-generating tool, a milling tool, a setting tool, or a similar tool.
Further, the driving unit may comprise projectable arms having wheels.
Also, the system as described above may comprise two driving units, an electrically driven driving unit and a fluid-driven driving unit.
In an embodiment, the tubing string may be a coiled tubing.
Also, the tubing string may be a casing.
A packer may be arranged surrounding the constant flow downhole assembly for isolating the casing in a first casing part and a second casing part, the first casing part comprising pressurised fluid for driving the turbine.
Moreover, the constant flow downhole assembly may have a first end and a second end, the first end being adapted to be connected with the tubing string, and the second end being adapted to be connected with the turbine.
The first end may have a male connection adapted to be connected with a female connection of the tubing string, and the second end may have a female connection adapted to be connected with a male connection of the turbine.
The present invention also relates to a constant flow downhole assembly for controlling a substantially constant flow rate in the downhole power system as described above, said constant flow downhole assembly having an assembly axis and comprising:
a body comprising a main bore having a bore inlet and at least one bore outlet,
a hollow piston having a piston inlet and a piston outlet, and being arranged in the main bore, and
a spring arranged in the main bore, said spring being compressed upon movement of the piston in a first direction.
In the constant flow downhole assembly as described above, the piston inlet may be smaller than the bore inlet so as to force the piston to move in the first direction.
Furthermore, the present invention relates to a method for proving a substantially constant flow of fluid into a turbine of the downhole power system as described above, comprising the steps of:
pressurising a fluid in a tubing string,
entering the pressurised fluid into the main bore of the constant flow downhole assembly,
letting the pressurised fluid flow past the hollow piston and into the turbine until the fluid flow exceeds a predetermined level,
moving a piston by the pressurised fluid pressing on a top of the piston, and
reducing a flow area of the bore outlet by the piston moving in a first direction until the fluid flow is substantially equal to the predetermined level.
The method for providing a substantially constant flow of fluid into a turbine of the downhole power system as described above may further comprise the steps of:
letting the pressurised fluid flow past the hollow piston and into the turbine until the fluid flow is below the predetermined level,
pressing onto the piston end wall in a second direction opposite the first direction by means of the spring, and
increasing the flow area of the bore outlet by movement of the piston until the fluid flow is substantially equal to the predetermined level.
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
a shows a diagram of a first test, and
b shows a diagram of a second test.
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.
Since the downhole power system is not dependent on a range of a wireline for powering a tool, the downhole power system is able to perform operations requiring more power than a wireline can deliver, also in a remote part of the well 11. The tubing string may be coiled tubing or drill pipe.
The downhole power system further comprises a generator 8 arranged between the turbine and the tool. The generator comprises a rotor 24 and a stator 25, and the rotor is connected with the shaft 5. When the shaft rotates the rotor, the generator is able to produce electrical power to the tool, and a wireline is hence no longer required for powering an electrical motor 20 driving the tool 6. In a downhole power system in which the tool can be operated by a rotational shaft, the generator can be dispensed with. In
The flow of fluid for ensuring optimal operation of the turbine is provided by the constant flow downhole assembly 7 connected with the tubing string so that a tubing string axis 14 is coincident with an assembly axis 9, as shown in
The piston in
Due to the design of the constant flow downhole assembly with a piston having a large opening in the piston end wall, through which the fluid can flow, and large cross-sectional areas of the fluid channels, the assembly can function in a downhole environment where the fluid is often “dirty” and contains elements or substances. Furthermore, by having a hollow piston, the constant flow downhole assembly can be designed as an elongated assembly having a substantially small diameter, and the constant flow downhole assembly is thus capable of fitting into a tool string in a downhole well.
The constant flow downhole assembly is a self-regulating valve and provides a substantially constant flow of fluid independent of the variations in the pressure in the tubing string. By varying the size of the piston inlet and/or the stiffness of the spring, the constant flow downhole assembly 7 can be designed to deliver from 80 litres/min. (0.5 barrels/min.) to 800 litres/min. (5 barrels/min.) at a pressure varying from 10 (145 PSI) to 700 bar (10,000 PSI), preferably from 140 bar (2,000 PSI) to 700 bar (10,000 PSI), and more preferably from 275 bar (4,000 PSI) to 700 bar (10,000 PSI).
In
The piston outlets 33 are, in
In
a shows a diagram displaying the flow rate of a first flow test which has been made on the constant flow downhole assembly in which no nozzles or restrictions were arranged in the first openings, and thus no means has been provided in the opening to restrict the flow into the bypass channel.
In
In order to provide a substantially constant flow of fluid into a turbine of the downhole power system, the downhole power system is entered into the well, and the tubing string is pressurised so that the pressurised fluid enters the main bore of the constant flow downhole assembly. The pressurised fluid flows past the hollow piston of the constant flow downhole assembly and into the turbine until the fluid flow exceeds a predetermined level. Then the piston is moved by the pressurised fluid pressing on the piston end wall, reducing a flow area of the bore outlet by the movement of the piston until the fluid flow is substantially equal to the predetermined level. Then the spring presses on the piston end wall and the flow area of the bore outlet is increased by the movement of the piston until the fluid flow is substantially equal to the predetermined level. Hereby, the constant flow downhole assembly ensures that a substantially constant flow is delivered to the turbine due to the balancing between the spring and the dynamic pressure of the flow to obtain a state of equilibrium.
A stroker tool is a tool providing an axial force. The stroker tool comprises an electrical motor for driving a pump. The pump pumps fluid into a piston housing to move a piston acting therein. The piston is arranged on the stroker shaft. The pump may pump fluid into the piston housing on one side and simultaneously suck fluid out on the other side of the piston.
By fluid or well fluid is meant any kind of fluid that may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By gas is meant any kind of gas composition present in a well, completion, or open hole, and by oil is meant any kind of oil composition, such as crude oil, an oil-containing fluid, etc. Gas, oil, and water fluids may thus all comprise other elements or substances than gas, oil, and/or water, respectively.
By a casing is meant any kind of pipe, tubing, tubular, liner, string etc. used downhole in relation to oil or natural gas production.
The driving unit may be a downhole tractor which may have projectable arms 31 having wheels 30 as shown in
Furthermore, the system may comprise several driving units where one is electrically driven as described above and another is fluid-driven and thus driven by the pressurised fluid in the tubing. The electrically driven driving unit is driven by the turbine generating electricity powering an electrical motor in the driving unit. The driving unit may have a hydraulic pump driven by the motor for driving the wheels and project the arms. In the fluid-driven driving unit, the pump is driven by the pressurised fluid.
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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12196526.3 | Dec 2012 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/076035 | 12/10/2013 | WO | 00 |