CN118043532A - Hydraulically driven downhole self-propelled cable tool - Google Patents

Abstract

A method for controlling a tool string having a downhole self-propelled wireline tool (1) with wheels (8) rotatable by hydraulic means and connected to a projectable arm assembly (6) projectable by hydraulic means, the method comprising lowering the downhole self-propelled wireline tool into a borehole, the downhole self-propelled wireline tool being connected to a second end (47) of a wireline (5) and a first end of the wireline being connected to a power source, the downhole self-propelled wireline tool having a tool body and a plurality of wheels rotatable by hydraulic means, and each wheel being connected to a projectable arm assembly projectable from the tool body by hydraulic fluid from a first hydraulic pump () 12, the downhole self-propelled wireline tool having an electric motor (4) rotatable at an operating speed for driving a first pump.

Description

Hydraulically driven downhole self-propelled cable tool

Technical Field

The present invention relates to a method for controlling a tool string having a downhole self-propelled cable tool having wheels that rotate by means of hydraulic means and are connected to an extendable arm assembly that extends by means of the hydraulic means. The present invention also relates to a hydraulically driven downhole self-propelled cable tool configured to perform the method.

Background technique

Interventions in the well are carried out for various reasons to perform operations, such as pulling casings, milling subs, pulling or setting plugs. The interventions in the well are usually powered by a cable and the working tool is propelled down the well to the location where the operation is to be performed by a self-propelled cable tool for pulling the cable as the working tool moves down to a more inaccessible, deviated or horizontal well portion. In order to be able to provide sufficient pulling force to pull the cable far down the well, the self-propelled cable tool is a hydraulically driven tool having wheels on its wheel arms, wherein each wheel is driven by a hydraulic motor in the wheel and the wheels are also pressed against the casing wall or the borehole by hydraulic means. Such hydraulically driven self-propelled cable tools provide greater pulling force than electrically driven self-propelled cable tools, but cannot be driven as quickly as electrically driven self-propelled cable tools.

In order to enable the hydraulically driven self-propelled cable tool to be driven faster, the hydraulic section of the hydraulically driven self-propelled cable tool has been developed in various ways. As known from WO2017/142415, one solution is that the front of the hydraulically driven wheels has been disconnected so that all the hydraulic power is used to drive the remaining wheels in order to drive faster. This solution is limited to two modes and therefore two speeds: a fast mode, in which only some wheels are driven by the hydraulic fluid and the other wheels are disconnected; a full-power mode, in which all wheels are driven by the hydraulic fluid, but at a very slow speed. In WO2019/004834, the hydraulic section is also provided with a bypass supply line so that the front of the hydraulic wheel can be bypassed instead of being disconnected, which therefore attempts to make the hydraulically driven self-propelled cable tool drive faster, but only with low pulling force; when a greater pulling force is required, some wheels are no longer bypassed, and then the speed of the self-propelled cable tool is reduced to a very low speed. In order to be able to better control the weight on bit/weight on the bit, the hydraulic section in WO2018/067018 is provided with a pressure setting valve configured to supply excess hydraulic fluid to a first hydraulic supply line for squeezing the wheels outwards, and then to a second hydraulic supply line for driving a hydraulic motor in the wheels, to increase the speed of the downhole tractor. However, delivering excess hydraulic fluid for squeezing the wheels outwards into the fluid flow for the rotational force compromises the maximum pulling force. Although several attempts have been made to develop faster hydraulically driven self-propelled cable tools with controllable hydraulic sections, such hydraulically driven self-propelled cable tools are either limited to two modes or compromise the maximum pulling force.

A disadvantage of electrically driven self-propelled cable tools is that they cannot provide sufficient pulling force for more difficult to access, deviated or horizontal well sections and cannot be operated in these sections because the electrically driven self-propelled cable tool cannot pull the cable as far. Therefore, attempts have been made to create a partially hydraulically driven and partially electrically driven self-propelled cable tool, but to date no success has been demonstrated.

Summary of the invention

An object of the present invention is to wholly or partly overcome the above-mentioned shortcomings and deficiencies in the prior art. More particularly, an object is to provide an improved method of controlling a hydraulically driven downhole self-propelled cable tool that can be driven faster without reducing the maximum pulling force.

Another object is to provide an improved method of controlling a hydraulically driven downhole self-propelled wireline tool that provides maximum available pulling force without sacrificing rapid drive capability due to current limitations in the cable.

The above objects and numerous other objects, advantages and features that will become apparent from the following description are achieved by the solution according to the present invention, namely by a method for controlling a tool string having wheels that rotate by means of hydraulic means and connected to an extendable arm assembly that protrudes by means of hydraulic means, the method comprising:

- lowering a downhole self-propelled cable tool into a wellbore, the downhole self-propelled cable tool being connected to a second end of a cable, a first end of the cable being connected to a power source, the downhole self-propelled cable tool having a tool body and a plurality of wheels rotatable by means of hydraulic means, each wheel being connected to an extendable arm assembly that can protrude from the tool body by means of hydraulic fluid from a first hydraulic pump, the downhole self-propelled cable tool having an electric motor that rotates at an operating speed for driving the first pump,

- Determine/specify the maximum permissible electrical power usage of the cable tool;

- supplying power to the downhole self-propelled wireline tool to cause the downhole self-propelled wireline tool to operate at a first speed, thereby forcing the downhole self-propelled wireline tool through the wellbore with a first force;

- determining a first maximum permissible operating speed of the electric motor based on a maximum permissible electrical power usage at a first predetermined motor output torque of the electric motor;

- determining the motor output torque of the electric motor; and

- compare whether the running speed exceeds the maximum permissible running speed of the motor under the determined motor output torque,

The method further includes adjusting the operating speed of the electric motor based on the result of the comparison so as to adjust the first speed to a second speed when the operating speed is higher than a maximum allowable motor speed.

Thus, a very simple method of adjusting the speed of a hydraulically driven downhole self-propelled wireline tool is provided, since only the motor is adjusted and not the more complex hydraulic sections to vary the speed of the hydraulically driven downhole self-propelled wireline tool.

When operating a cable tool, the operation of the cable tool at a power level is limited by how much power the cable can deliver. By defining the maximum allowable electrical power usage of the cable tool, it is ensured that the cable tool operates at a power level that does not exceed the power limit set for the cable and/or cable tool.

Furthermore, by having the maximum allowable electrical power usage of the cable tool, a first maximum allowable operating speed of the electric motor at a predetermined motor output torque can be determined. Thus, when the motor is running at a first motor speed, the maximum allowable electrical power usage can be used to find a limit/limit on how much torque the motor can have at a predetermined motor speed.

By determining the motor output torque of the electric motor during operation, it can be seen whether the maximum permissible speed at the determined motor output torque exceeds a limit. This can be done by comparing whether the operating speed exceeds the maximum permissible operating speed of the electric motor at the determined motor output torque, and wherein the method adjusts the operating speed to ensure that the operating speed does not exceed the maximum operating speed at the determined motor output torque.

Thus, it is ensured that the self-propelled cable tool can adjust its motor speed during use to ensure that the motor operates within the power limit of the cable. Thus, the method allows the cable tool to operate within the limits of the maximum permissible electrical power usage, thereby protecting the components of the cable tool from operating beyond their capacity.

The method may further include continuously determining the motor output torque by calculation from electrical phase measurements of the electric motor.

The method may further include calculating a maximum allowable operating speed of the electric motor by using each determined motor output torque.

The maximum permissible electrical power usage (effect) is given by the maximum permissible current allowed to flow in the cable at a predetermined voltage and/or a constant voltage, and the maximum permissible operating speed of the electric motor is obtained by determining the determined (actual) motor output torque and dividing the maximum effect by the actual motor output.

If the operating speed of the electric motor is higher than the maximum allowable operating speed of the electric motor, the operating speed of the electric motor may be decreased, and if the operating speed of the electric motor is lower than the maximum allowable operating speed of the electric motor, the operating speed of the electric motor may be increased.

The method may further include determining a second maximum allowable operating speed of the electric motor based on a maximum allowable electrical power usage at a second predetermined motor output torque of the electric motor.

The method may also further include determining a third, fourth or subsequent maximum allowable operating speed for the electric motor based on the maximum allowable electrical power usage at a third, fourth or subsequent predetermined motor output torque of the electric motor.

The downhole self-propelled cable tool may also include a pressure sensor and a hydraulic section, wherein the pressure sensor continuously measures a second fluid pressure of a second fluid used to rotate the wheel, and the hydraulic section includes a first controllable valve that controls a first fluid pressure used to extend the arm assembly based on the second fluid pressure.

The hydraulic section can control the first fluid pressure by adjusting the first controllable valve based only on the second pressure, so as to optimize the supply of sufficient but no more than required power to the wheel arm. Therefore, the speed of the hydraulically driven downhole self-propelled cable tool is continuously adjusted using all available power (i.e., below the current limit) so as to be driven at the maximum speed or at the required force and the corresponding maximum allowed speed, and the hydraulically driven downhole self-propelled cable tool can be driven at the maximum speed until the force required to pull the cable increases to a first force in the power limit curve, above which it is necessary to reduce the speed and therefore the rotational speed of the electric motor so as not to exceed the current limit. Therefore, the hydraulically driven downhole self-propelled cable tool can be self-controlled so as to continuously adjust its speed to the maximum value without exceeding the cable current limit.

By having a first controllable valve for controlling a first fluid pressure based on a second pressure, continuous control of the hydraulically driven downhole self-propelled cable tool is further optimized to ensure that no power is wasted in extending the extendable arm assembly outwardly toward the wall of the well, beyond that required to obtain optimal friction between the wheels and the wall to drive the hydraulically driven downhole self-propelled cable tool forward.

Furthermore, adjusting the operating speed of the electric motor based on the result of the comparison may be performed independently of any condition of the cable, such as pull in the cable, cable tension, or cable resistance.

Furthermore, adjusting the operating speed of the electric motor based on the results of the comparison may be performed independently of any pump conditions such as pump flow, pump pressure, or stroke length.

Furthermore, adjusting the operating speed of the electric motor based on the results of the comparison may be performed independently of any speed conditions of the downhole self-propelled wireline tool.

Furthermore, the first speed of the downhole self-propelled wireline tool may be adjusted to a second speed by adjusting the operating speed of the electric motor.

Additionally, the method may include determining an operating speed of the electric motor.

Furthermore, determining the output torque of the electric motor may be performed by measuring the currents of the three phases in the electric motor.

Additionally, the method may further include measuring a current demand/input of the electric motor and measuring a voltage input of the electric motor.

Additionally, determining the maximum allowable motor speed based on the motor output torque may be based on a measured current and a measured voltage of the electric motor.

Furthermore, by measuring the actual current demand and voltage of the electric motor, the maximum permissible motor speed may be determined more accurately, since the efficiency of the electric motor varies depending on the speed at which the electric motor is operating. Thus, for the same power output, the current demand at high speeds is lower than the current demand at low speeds, and the maximum power may therefore vary to be slightly greater at high speeds than if the maximum power were assumed to be constant.

Furthermore, the regulation of the operating speed of the electric motor may be based on a measured current demand of the electric motor or a calculated load of the electric motor.

Furthermore, the regulation of the operating speed of the electric motor can be performed continuously.

Furthermore, the current demand of the electric motor may be measured by a motor drive at or in the electric motor.

Furthermore, determining the maximum allowable motor speed based on the motor output torque may also be based on a preset value of the maximum power or the maximum current.

In addition, each wheel may include a hydraulic motor for rotating the wheel to provide self-propelled movement, each wheel is connected to the second arm end of one of the extendable arm assemblies, and the multiple extendable arm assemblies are movably connected to the tool body at the first arm end and can be extended from the tool body with the aid of a first fluid having a first fluid pressure, and the downhole self-propelled cable tool also includes a pressure sensor that continuously measures the first fluid pressure.

Furthermore, each hydraulic motor may be driven by a second fluid having a second fluid pressure from the first hydraulic pump or from a second hydraulic pump driven by the electric motor.

Furthermore, regulation of the speed of the electric motor may be based on the first fluid pressure.

Additionally, the method may further include controlling the first fluid pressure based on the second pressure via a first controllable valve in a hydraulic section of the downhole self-propelled wireline tool.

Additionally, the method may further comprise measuring a rotational speed of the electric motor.

Additionally, the method may further include determining a load on the motor based on the torque output.

Additionally, the hydraulic section may include a first pressure sensor that continuously measures a second fluid pressure of the second fluid, and the adjustment of the operating speed of the electric motor may be based on the second fluid pressure.

Additionally, the downhole self-propelled wireline tool may further include a machining tool for performing a machining operation and a compression fitting including a load cell adjacent the machining tool.

Furthermore, the downhole self-propelled wireline tool may further include a logging tool, and the operating speed may be set to a predetermined constant operating speed of the electric motor.

In addition, the downhole self-propelled cable tool may also include an operating tool with a drill bit for performing downhole operations (such as milling), and the method may also include measuring a second fluid pressure and estimating a weight on the drill bit/bit pressure (WOB), comparing the estimated weight on the drill bit with a predetermined weight on the drill bit, and adjusting the second fluid pressure based on the result of the comparison.

In addition, the downhole self-propelled cable tool may also include a compression joint and an operating tool with a drill bit for performing downhole operations (such as milling), and the method may also include measuring the weight on the drill bit with the aid of the compression joint, comparing the measured weight on the drill bit with a predetermined weight on the drill bit, and adjusting the second fluid pressure based on the result of the comparison.

Furthermore, the downhole self-propelled wireline tool may further include a second hydraulic pump for generating a first fluid pressure for extending the plurality of extendable arm assemblies.

Furthermore, the hydraulic section may further include a second controllable valve for controlling the pressure of the second fluid.

Furthermore, the downhole self-propelled wireline tool may further comprise a compensator for providing a predetermined overpressure in the tool.

In addition, the downhole self-propelled cable tool may further include a surface readout module for sending measured tool parameters to the surface, such as the first fluid pressure, the second fluid pressure, the operating speed of the electric motor, and the output torque of the electric motor.

Additionally, the electric motor may include a motor driver that measures the operating speed of the electric motor.

Furthermore, the electronic control unit may be configured to determine a motor output torque of the electric motor.

Furthermore, the electronic control unit may include a capacitor which serves as an energy storage unit or accumulator.

Furthermore, the hydraulic section may also comprise a second pressure sensor.

Furthermore, the controllable valve may be a controllable pressure reducing valve.

The present invention also relates to a tool string comprising two downhole self-propelled cable tools installed as one cable tool string, wherein each downhole self-propelled cable tool has a separate electronic control unit, a separate electric motor, one or two separate hydraulic pumps, a separate hydraulic section, and one or more separate drive sections.

The present invention also relates to a tool string, comprising a first downhole self-propelled cable tool, the first downhole self-propelled cable tool comprising:

- Tool body;

- an electric motor running at a rotational speed and powered by an electric cable;

- a plurality of extendable arm assemblies movably connected to the tool body at a first arm end and extendable from the tool body by means of a first fluid having a first fluid pressure;

- a plurality of wheels for contacting the wall of the well, each wheel comprising a hydraulic motor for rotating the wheel to provide self-propelled movement, each wheel being connected to the second arm end of one of the arm assemblies;

- a first hydraulic pump driven by the electric motor for generating a second fluid pressure of a second fluid for driving the hydraulic motor to rotate the wheels; and

- a first pressure sensor continuously measuring the pressure of the second fluid,

The downhole self-propelled cable tool further comprises a hydraulic section, wherein the hydraulic section comprises a first controllable valve for controlling the first fluid pressure based on the second fluid pressure,

The tool string further comprises a second downhole self-propelled cable tool, the second downhole self-propelled cable tool comprising:

- Tool body;

- a second electric motor, which runs at a rotational speed and is powered by the cable;

- a plurality of extendable arm assemblies movably connected to the tool body at a first arm end and extendable from the tool body by means of a third fluid having a third fluid pressure;

- a plurality of wheels for contacting the wall of the well, each wheel comprising a hydraulic motor for rotating the wheel to provide self-propelled movement, each wheel being connected to the second arm end of one of the arm assemblies;

- at least one second hydraulic pump driven by the second electric motor, the second hydraulic pump for generating a fourth fluid pressure of a fourth fluid for driving the hydraulic motor to rotate the wheels; and

- a pressure sensor for continuously measuring the pressure of said fourth fluid,

The second downhole self-propelled cable tool also includes a second hydraulic section, the second hydraulic section includes a third controllable valve that controls the third fluid pressure based on the fourth fluid pressure, and the first downhole self-propelled cable tool is connected to the cable at one end and to the second downhole self-propelled cable tool at the other end.

In addition, the step of lowering may include lowering the first and second downhole self-propelled cable tools into the wellbore, and the step of supplying power may include supplying power to the first and second downhole self-propelled cable tools so as to operate the first and second downhole self-propelled cable tools at a first speed, thereby forcing the tool string to pass through the wellbore with a first force, the step of determining may include determining the motor output torque of the first and second electric motors, the step of determining may include determining the maximum allowable motor speed based on the motor output torque of the first and second electric motors, the step of comparing may include comparing the operating speed of the first and second electric motors with the maximum allowable motor speed, wherein the step of adjusting may include adjusting the operating speed of the first and second electric motors based on the result of the comparison so as to adjust the first speed to the second speed when the operating speed is higher than the maximum allowable motor speed.

Furthermore, each electric motor may further comprise a power or current limiting unit for allocating a first portion of the current from the cable to power the first electric motor and a second portion of the current to power the second electric motor.

Additionally, the first and second downhole self-propelled wireline tools may be electrically connected in parallel.

Furthermore, the downhole self-propelled wireline tool may further comprise a current distribution unit for distributing a first portion of the current from the cable to power the first electric motor and a second portion of the current to power the second electric motor.

Furthermore, the downhole self-propelled wireline tool may include a current distribution unit instead of a power limiting unit to distribute a first portion of the current from the cable to power the first electric motor and a second portion of the current to power the second electric motor.

Finally, the present invention relates to a hydraulically driven downhole self-propelled wireline tool configured to carry out the above method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its many advantages will be described in more detail below with reference to the attached schematic diagrams which show only some non-limiting embodiments for illustrative purposes, in which:

FIG1 shows a downhole self-propelled wireline tool according to the present invention having two pulley sections driven by an electric motor and a hydraulic pump;

FIG2 shows another downhole self-propelled wireline tool according to the present invention, which has two pulley sections driven by an electric motor and two hydraulic pumps;

FIG3 shows another downhole self-propelled wireline tool according to the present invention, which has two pulley sections, each of which is driven by an electric motor and a hydraulic pump;

FIG4 shows another downhole self-propelled wireline tool comprising a compression joint and an operating tool for performing an operation in a well, such as milling/grinding with a drill bit;

FIG5 shows a downhole self-propelled wireline tool control method with some optional steps according to the present invention;

FIG6 shows another downhole self-propelled wireline tool control method with some optional steps for performing downhole operations;

FIG7 shows another downhole self-propelled wireline tool control method; and

FIG. 8 shows a graph of power as a function of pulling force and speed of the tool.

All the figures are highly schematic and not necessarily to scale, and they show only those components which are necessary in order to elucidate the invention, other components being omitted or merely suggested.

Detailed ways

FIG1 shows a downhole self-propelled cable tool 1 for propelling the tool forward in a wellbore 2 and possibly also for providing weight on a drill bit 39 when performing operations, as shown in the tool 1 of FIG2 . The downhole self-propelled cable tool 1 comprises a tool body 3 and an electric motor 4 running at an operating speed and powered by a cable 5. The downhole self-propelled cable tool 1 also comprises a plurality of extendable arm assemblies 6 and a plurality of wheels 8 for contacting a wall 9 of a well, the extendable arm assemblies 6 being movably connected to the tool body 3 at a first arm end 7 and being extendable from the tool body 3 by means of a first fluid having a first fluid pressure. Each wheel comprises a hydraulic motor 10 for rotating the wheel to provide self-propelled movement, and each wheel 8 is connected to a second arm end 11 of one extendable arm assembly 6 so that when the arm is extended, the wheel engages the wall. The electric motor 4 is configured to drive a first hydraulic pump 12 by rotation for generating a second fluid pressure for driving the hydraulic motor 10 for rotating the wheels 8. The downhole self-propelled cable tool 1 is connected to a second end 47 of the cable 5, the first end of which is connected to a power source (not shown) on the surface or on the seafloor. The downhole self-propelled cable tool 1 also includes an electronic control unit 18 and a cable head 44 for connecting the tool to the cable 5. The downhole self-propelled cable tool 1 also includes a hydraulic section 15 for controlling the fluid from the pump 12 to the wheel 8 and the arm assembly 6.

The electronic control unit 18 controls the speed of the electric motor 4, thereby also controlling the speed of the pump and the tool speed of the downhole self-propelled cable tool 1 along the longitudinal extension direction of the well, because the pump generates a fluid flow into the wheel 8. At the beginning of the well closest to the top of the well, the downhole self-propelled cable tool 1 requires very little force to pull the cable 5 and the tool together, but as the downhole self-propelled cable tool 1 moves downhole, the tool 1 requires more and more force to pull the cable 5. As the required force increases, the wheel 8 requires a higher pressure to rotate, so the pump 12 requires a greater rotational force from the motor 4, that is, the motor output torque. In the case of using such a downhole self-propelled cable tool 1, the cable used for the intervention operation is rated for a maximum current limit, which depends on the length of the cable or other cable parameters. Therefore, it is important not to exceed such a current limit. By assuming, calculating or measuring the voltage, the power limit P of the operation is also known, and the power limit P is shown in Figure 8. The power limit can also be understood as the maximum allowable electrical power usage of the cable tool. As the motor output torque increases, the current demand increases accordingly, and when the limit is reached, the downhole self-propelled cable tool 1 needs to reduce its speed, i.e. move along the power limit curve in Figure 8. When operating the downhole self-propelled cable tool at a low speed, the maximum force available (e.g., the force used to pull the cable) is very large; however, if this high force is not utilized to the maximum extent, the first pressure at which the protruding arm and therefore the wheel are pressed against the inner surface of the casing/tubular metal structure may be unnecessarily high, resulting in unnecessary wear of the wheels. Similarly, when the downhole self-propelled cable tool is operated without using a large force, such as for pulling in the cable, the downhole self-propelled cable tool may be driven at a high speed; however, if the downhole self-propelled cable tool drives into an obstacle at a high speed, the downhole self-propelled cable tool may shut down or be severely damaged. Therefore, the method may include a step of reducing the second fluid pressure and/or the first fluid pressure to avoid unnecessary wear of the wheels or to avoid parking.

A method 100 for controlling a tool string having a downhole self-propelled cable tool 1 is shown in Figure 5. The method comprises: lowering 110 the downhole self-propelled cable tool 1 into a wellbore 2; supplying 120 power to the downhole self-propelled cable tool so as to operate the downhole self-propelled cable tool at a first speed so as to force the downhole self-propelled cable tool through the wellbore 2 with a first force; determining 130 the motor output torque of the electric motor; determining 140 the maximum allowable motor speed based on the motor output torque so as to compare 150 the operating speed with the maximum allowable motor speed; and then adjusting 160 the operating speed of the electric motor 4 based on the result of the comparison so as to adjust the first speed to a second speed if the operating speed is higher than the maximum allowable motor speed.

Thus, a very simple method of adjusting the speed of the hydraulically driven downhole self-propelled wireline tool 1 is provided, since only the electric motor 4 is adjusted, and not the more complex hydraulic section 15 to change the speed of the hydraulically driven downhole self-propelled wireline tool 1. Adjustment of the electric motor will also affect the speed more quickly, since hydraulic adjustment is always slower than electronic adjustment.

Thus, if necessary, the speed of the hydraulically driven downhole self-propelled cable tool 1 is continuously adjusted using all available power (i.e. below the current limit) in order to be driven at the maximum speed or at the required force and the corresponding maximum allowed speed. The hydraulically driven downhole self-propelled cable tool 1 can be driven at the maximum speed until the force required to pull the cable increases to a first force F1 (as shown in FIG8 ) that is in the power limit curve, above which it is necessary to reduce the speed and therefore the rotation speed of the electric motor 4 so as not to exceed the current limit, but the speed of the tool 1 is only adjusted to a speed at which the electric motor 4 can still provide the tool with sufficient torque to pull the cable 5. Thus, the hydraulically driven downhole self-propelled cable tool 1 controls itself to continuously adjust its speed to the maximum value without exceeding the current limit of the cable 5 and without significantly reducing the maximum pulling force.

A known hydraulically driven downhole self-propelled cable tool can shut down one or more drive sections, thereby using the remaining active drive sections to drive faster at a maximum speed and a very low first pulling force; as shown in FIG8, when a greater pulling force is required, all drive sections are turned on, and the downhole self-propelled cable tool is then driven at a second minimum speed and maximum pulling force. When at a certain point in the well, due to the current limitation in the cable, the pulling force required to pull the cable when the tool is driven at maximum speed becomes too high, then the known self-propelled cable tool with only two modes needs to turn on other drive sections to continue driving, and can only drive slower from this point. From this point until the point where the maximum pulling force is required is reached, the known self-propelled cable tool does not use all the available power, which is represented as area A in FIG8. Therefore, even if some known self-propelled cable tools are able to drive quickly when a large pulling force is not required, the hydraulically driven downhole self-propelled cable tool controlled according to the present method will reach the destination in the well faster, because the control of the hydraulically driven downhole self-propelled cable tool enables the speed to be continuously adjusted using all available power, i.e. below the current limit. Known self-propelled cable tools are typically set to drive at a speed lower than the maximum speed because the tool can then generate more pulling force and thus drive further before having to engage other drive sections, and therefore known tools are typically driven slower than tools controlled according to the present invention.

In FIG. 8 , the maximum speed of the hydraulically driven downhole self-propelled wireline tool 1 is based on the maximum permissible rotational speed of the electric motor 4 , and the maximum pulling force is based on the minimum permissible rotational speed of the electric motor 4 .

The power curve shown in Figure 8 can be defined by determining the maximum allowable electric power usage of the cable tool and determining the maximum allowable operating speed of the electric motor based on the maximum allowable electric power usage at a predetermined motor output torque of the electric motor. When the operating speed of the electric motor decreases, the motor output torque of the electric motor can increase. Line/curve P can be regarded as the product of the motor output torque and the operating speed of the electric motor, where a decrease in speed allows an increase in the motor output torque, but an increase in speed limits the allowable motor output torque. If the operating speed of the electric motor is too high at a determined motor output torque so that the maximum allowable electric power usage of the cable tool is not exceeded, the operating speed can be reduced.

The motor output torque can be continuously determined from the electrical phase/phases, and by using each determined motor output torque, the maximum allowable operating speed of the electric motor can be calculated and compared with the operating speed of the electric motor, and if the operating speed of the electric motor is higher than the maximum allowable operating speed of the electric motor, the operating speed of the electric motor can be reduced, and if the operating speed of the electric motor is lower than the maximum allowable operating speed of the electric motor, the operating speed of the electric motor can be increased. Curve P represents the maximum allowable electrical power usage of the cable tool, and is defined by finding the speed limit at which the operating speed is at a predetermined motor output torque. By performing this determination at two, three, four, five different speeds of the electric motor, a power curve can be defined, wherein the method allows the cable tool to operate within the limits of the maximum allowable electrical power usage, thereby protecting the cable and the components of the cable tool from operating beyond their capacity.

The curve P shown in Figure 8 has a first axis, which may be the motor output torque, and a second axis, which may be the operating speed. Therefore, if the product of the motor output torque and the operating speed is higher than the curve P, the operating speed of the electric motor may be reduced to ensure that the cable tool operates below the curve P and/or within the shaded area A, as shown in Figure 8. Similarly, if the product of the motor output torque and the operating speed is higher than the curve P, the operating speed of the electric motor may be increased to ensure that the cable tool operates at the maximum allowable speed, thereby optimizing the full utilization of the maximum allowable electrical power usage of the cable tool.

The electrical power corresponds to the mechanical power required, for example, to rotate and drive a pump, but is less than the electrical power due to electrical losses in tool components, motors, etc. The losses of a motor at high torque and low speed are higher than at low torque and high speed.

In the method of Figure 5, the adjustment of the operating speed of the electric motor 4 based on the result of this comparison is made independently of any condition of the cable 5, such as cable pull, cable tension or cable resistance. The cable has a certain flexibility and may vary from well to well, so if such cable conditions are not known when the downhole self-propelled cable tool is being lowered into the well, the method is advantageous and is also applicable to all wells and cables, even in the absence of an advanced control cable unit at the top of the drilling rig or well.

Furthermore, in the method of FIG. 5 , the adjustment of the operating speed of the electric motor 4 based on the result of this comparison is made independently of any pump conditions such as pump flow, pump pressure or stroke length. Due to the limited space in the well, it is difficult to make room for the measuring wires in the pump section, because the pumping capacity will be greatly reduced, and the maximum speed of the downhole self-propelled wireline tool will also be reduced. Therefore, by controlling the downhole self-propelled wireline tool 1 according to the present method, the hydraulic pump is designed to use the full diameter of the tool, so that the maximum speed is significantly increased compared to known tools.

Thus, the first speed of the downhole self-propelled wireline tool 1 is adjusted to the second speed by adjusting the operating speed of the electric motor 4. Control is performed without determining the power used, but only by determining 130 the motor output torque of the electric motor 4, determining 140 the maximum permissible motor speed based on the motor output torque, and comparing 150 the operating speed with the maximum permissible motor speed.

In FIG. 5 , the method of controlling a downhole self-propelled wireline tool 1 may further include determining 145 the rotational speed of the electric motor 4 , and the output torque of the electric motor may be determined by measuring 125 the current on three phases of the electric motor.

As can be seen from FIG. 5 , the method may further comprise measuring 135 the current demand/input of the electric motor 4 and measuring 135 b the voltage input of the electric motor, and thus determining 140 the maximum permissible motor speed based on the motor output torque may also be based on the measured current and measured voltage of the electric motor. By measuring the actual current demand and voltage of the electric motor 4, the maximum permissible motor speed may be determined more accurately, since the efficiency of the electric motor varies depending on the operating speed of the electric motor. Thus, for the same output power of the motor, the current demand at high speed is relatively lower than the current demand at low speed, because of the varying efficiency of the electric motor 4, and the maximum power may therefore vary to be slightly greater at high speed than when the maximum power is assumed to be constant. In this way, the downhole self-propelled cable tool 1 can be driven at an even higher maximum speed, and the maximum pulling force is also increased.

The permissible efficiency of the electric motor 4 varies with temperature, so at lower temperatures, for example below 200° C., the electric motor may operate at a higher efficiency than at higher temperatures. Therefore, the downhole self-propelled wireline tool may include a temperature sensor for measuring the temperature of the electric motor and adjusting the permissible efficiency level of the motor accordingly.

As shown in FIG. 7 , the adjustment 160 a of the operating speed of the electric motor 4 may also be based on a measured current demand of the electric motor or a calculated load of the electric motor.

The regulation of the operating speed of the electric motor can be continuously performed in order to optimize the tension F and speed of the tool so as to keep the power demand below the power curve P of the graph relating the tension and speed of the tool in region A shown in FIG8. In this way, all the available power is used in an optimal way to ensure that the downhole self-propelled wireline tool is driven at maximum speed while being able to provide the required tension at any position in the well.

In FIG1 , the electronic control unit 18 includes a motor driver 28, a main controller and/or a voltage inverter. According to the method of FIG5 , the electronic control unit 18 determines 145 or the motor driver 28 determines 145a the operating speed of the electric motor 4, and the motor driver 28 is configured to measure 125 the current on the three phases of the motor to determine 130 the motor output torque of the electric motor 4. The electronic control unit 18 or the motor driver 28 is configured to determine 140 the maximum allowable motor speed based on the motor output torque, and compare 150 the operating speed with the maximum allowable motor speed, and then adjust 160 the operating speed of the electric motor 4 based on the result of the comparison, so as to adjust the first speed to the second speed when the operating speed is higher than the maximum allowable motor speed. Optionally, the maximum allowable motor speed determined 140 based on the motor output torque can also be based on a preset value 142 of the maximum power or the maximum current. Additionally, ECU 18 or motor driver 28 may measure 135 current demand/input of electric motor 4 and measure 135 voltage input of the electric motor and determine 140 a maximum allowable motor speed based on motor output torque which may also be based on the measured current and measured voltage of electric motor 4 .

In FIG. 6 , the method comprises continuously measuring 130d the second fluid pressure by means of the first pressure sensor 49 , and the adjustment 160c of the rotation speed of the electric motor 4 is based on the second fluid pressure, in addition to or instead of steps 130 - 150 .

5, 6 and 7 further comprises controlling 170 the first fluid pressure based on the second fluid pressure by means of a first controllable valve 16 in the hydraulic section 15 of the downhole self-propelled wireline tool 1. The method may also optionally comprise determining 180 a load on the electric motor 4 based on the torque output.

In FIG. 6 , the method comprises continuously measuring 130b a second fluid pressure of a second fluid, and adjusting 160d the operating speed of the electric motor 4 based on the second fluid pressure, in addition to or instead of steps 130 - 150 .

As shown in FIG1 , the downhole self-propelled cable tool 1 further comprises a first pressure sensor 49 that continuously measures the second fluid pressure of the second fluid to drive each hydraulic motor 10 to rotate the wheel 8, and a hydraulic section 15 that comprises a first controllable valve 16 that controls the first fluid pressure for extending the arm assembly 6 based on the second fluid pressure. The hydraulic section 15 can adjust only the first controllable valve 16 for controlling the first fluid pressure based on the second pressure, thereby ensuring that sufficient power is provided to the wheel arm 6, but not more than the required power. By having the first controllable valve 16 that controls the first fluid pressure based on the second pressure, the continuous control of the hydraulically driven downhole self-propelled cable tool 1 is even further optimized, so that no power is wasted in extending the extendable arm assembly 6 outward toward the wall of the well, except for the power required for obtaining the best friction between the wheel 8 and the wall to drive the hydraulically driven downhole self-propelled cable tool 1 forward.

By having the first controllable valve 16 control the first fluid pressure based on the second pressure, the wheels 8 are not pressed outward more than necessary. The higher the second fluid pressure, the higher the first pressure needs to be in order to optimally propel the downhole self-propelled cable tool 1 forward in the well. When there is a low second pressure, the first pressure is adjusted to match the low second pressure so that power is not wasted to provide a higher than required first fluid pressure. In addition, if the first fluid pressure is higher than the optimal first fluid pressure that matches the current second fluid pressure, too much friction is applied to the wall of the well, thereby compromising the maximum available rate of the downhole drive unit.

The first pressure sensor 49 continuously measures the second fluid pressure, and data representing the measured second fluid pressure is transmitted to the electronic control unit. When the second fluid pressure changes, the electronic control unit electrically controls the first controllable valve by conducting electricity to the valve to move the valve to an open position that is more open or less open, so that the first controllable valve 16 controls the first fluid pressure based on the second fluid pressure. Therefore, the sensor and valve can be regarded as a feedback loop, in which the measured value is fed back to control the valve, so that an increase or decrease in the second fluid pressure is used to provide a resulting action on the valve to increase or decrease the pressure to extend the arm based on the rotational speed of the wheel.

In FIG. 1 , a first hydraulic pump 12 generates a first fluid pressure for extending the plurality of extendable arm assemblies 6 , and in FIG. 2 , the downhole self-propelled cable tool 1 further includes a second hydraulic pump 14 for generating a first fluid pressure for extending the plurality of extendable arm assemblies 6 .

As shown in FIG1 , the hydraulic section 15 also includes a second controllable valve 17 for controlling the pressure of the second fluid. The controllable valves 16, 17 are electronically adjustable. The downhole self-propelled cable tool 1 has two pulley sections/drive sections 30, one of which is rotated 90 degrees around the circumference of the tool relative to the other pulley section in order to center the tool in the well. In other operations where centering is not important, the downhole self-propelled cable tool 1 has only one drive section 30, as shown in FIG2 . Such operations may be milling or grinding operations, in which the downhole self-propelled cable tool includes an operating tool as shown in FIG2 .

The downhole self-propelled wireline tool 1 further comprises a compensator 35 for providing a predetermined overpressure in the tool so that wellbore fluid does not enter the tool and jeopardize the function of the tool and so that dirty wellbore fluid does not mix with the hydraulic fluid in the tool.

The downhole self-propelled cable tool 1 further comprises a surface readout module 29 for sending measured tool parameters to the surface, such as the first fluid pressure, the second fluid pressure, the operating speed of the electric motor 4 and/or the motor output torque.

In FIG2 , the downhole self-propelled cable tool 1 includes an operating tool 38, such as a logging tool 38b (as shown in FIG4 ) or a machining tool 32, having a compression joint 33 and a drill bit 39 for performing machining operations, the compression joint including a load cell 34 adjacent to the machining tool to measure the actual weight on the drill bit. The operating tool 38 also includes an electronic control unit 40, a compensator 41, an electric motor 42 and a gear section 43, the gear section being used to rotate the drill bit 39 at another speed different from the speed of the motor 42, which usually rotates at a lower speed. The compression joint 33 including the load cell 34 is arranged between the electronic control unit 40 and the drive section 30, the drive section including the wheel 8 on the extendable arm assembly 6.

When the downhole self-propelled wireline tool 1 also includes a logging tool 38 b and the downhole self-propelled wireline tool has propelled itself to a point where a logging operation is to be performed, the operating speed is set to a predetermined constant operating speed of the electric motor 4 .

As shown in Figure 6, when the downhole self-propelled cable tool 1 also includes an operating tool 32 having a drill bit 39 for performing downhole operations (such as milling), and the downhole self-propelled cable tool has advanced itself to a point where the milling operation is to be performed, the method also includes measuring 130b the second fluid pressure, estimating 140c the weight on the drill bit/weight on bit (WOB), comparing 150a the estimated weight on the drill bit with a predetermined weight on the drill bit, and adjusting 160e the second fluid pressure based on the result of the comparison. Steps 130b, 140c, 150a and 160e may be in addition to or in place of steps 130-160.

As shown in Figure 6, when the downhole self-propelled cable tool 1 also includes a compression joint 33 and an operating tool 32 having a drill bit 39 for performing downhole operations (such as milling), the method may also include measuring 130c the weight on the drill bit through the compression joint, comparing 150b the measured weight on the drill bit with a predetermined weight on the drill bit, and adjusting 160f the second fluid pressure based on the result of the comparison. Steps 130c, 150b and 160f may be a supplement or alternative to steps 130-160.

In FIG3 , the electric motor 4 is a first electric motor 4, and the downhole self-propelled cable tool 1 includes a second electric motor 22 driving a second hydraulic pump 14, and the first electric motor 4 drives the first hydraulic pump 12. The first electric motor 4 thus drives the first hydraulic pump 12 for producing a fluid for extending the extendable arm assembly 6 and for rotating the wheels 8 of one drive section 30a, and the second electric motor 22 thus drives the second hydraulic pump 14 to produce a fluid for extending the extendable arm assembly 23 and a fluid for rotating the wheels 24 of the second drive section 30b. The second hydraulic pump 14 produces a third fluid pressure for the extension of the second plurality of extendable arm assemblies 23. The second hydraulic pump 14 produces a fourth fluid pressure for driving the hydraulic motor 10 to rotate the second plurality of wheels 24. The hydraulic section 15 for the first drive section 30a is the first hydraulic section 15, and the downhole self-propelled cable tool 1 also includes a second hydraulic section 25, which includes a third controllable valve 26 for controlling the pressure of the third fluid and a fourth controllable valve 27 for controlling the pressure of the fourth fluid. The first controllable valve 16 and the second controllable valve 17 can be electrically controlled by the electronic control unit 18, and the third controllable valve 26 and the fourth controllable valve 27 can be electrically controlled by the second electronic control unit 18b. The first electric motor 4 and/or the second electric motor 22 are synchronous motors.

Thus, the tool string of FIG3 is two downhole self-propelled wireline tools 1 mounted as one wireline tool, wherein each wireline tool has a separate electrical control unit, a separate electric motor, one or two separate hydraulic pumps, a separate hydraulic section and one or more separate drive sections 30. The first downhole self-propelled wireline tool 1a comprises an electrical control unit 18, an electric motor 4, one or two hydraulic pumps 12, a hydraulic section 15 and drive sections 30, 30a having wheels 8 on an extendable arm assembly 6. The second downhole self-propelled wireline tool 1b comprises an electrical control unit 18b, a second electric motor 22, one or two hydraulic pumps 14, a hydraulic section 15 and drive sections 30, 30b having wheels 24 on an extendable arm assembly 23. The plurality of extendable arm assemblies 23 are movably connected to the tool body 3 at the first arm end 7b, and each wheel includes a hydraulic motor 10b for rotating the wheel to provide self-propelled movement, and each wheel is connected to the second arm end 11b of one of the arm assemblies 23. The first downhole self-propelled cable tool 1a is connected to the cable head 44 and the cable 5. The hydraulic section 15 is configured to measure the first and second fluid pressures through the first pressure sensor 49 and the second pressure sensor 48, and control the valve based on the measured first and second fluid pressures. The second hydraulic section 25 is configured to measure the third and fourth fluid pressures through the third pressure sensor 48b and the fourth pressure sensor 49b, and control the valve based on the measured third and fourth fluid pressures. The controllable valves 16, 17, 26, 27 are controllable pressure reducing valves. Therefore, the power of the tool string is evenly distributed between the first and second electric motors 4, 22, so that each electric motor is limited to half of the current limit to ensure that the tool string does not exceed the allowable current limit on the cable.

The step of lowering 110 includes lowering the first and second downhole self-propelled cable tools 1, 1a, 1b into the wellbore 2, the step of supplying 120 power includes supplying power to the first and second downhole self-propelled cable tools 1, 1a, 1b so as to operate the first and second downhole self-propelled cable tools 1, 1a, 1b at a first speed, thereby forcing the tool string through the wellbore 2 with a first force, the step of determining 130 includes determining the motor output torque of the first and second electric motors 4, 22, the step of determining 140 includes determining the maximum allowable motor speed based on the motor output torque of the first and second electric motors 4, 22, the step of comparing 150 includes comparing the operating speed of the first and second electric motors 4, 22 with the maximum allowable motor speed, and wherein the step of adjusting 160 includes adjusting the operating speed of the first and second electric motors 4, 22 based on the comparison result so that if the operating speed is higher than the maximum allowable motor speed, the first speed is adjusted to the second speed.

In FIG3 , the electronic control unit 18 further comprises a voltage control unit 19 and a current measuring unit 20, the voltage control unit having an overvoltage protection unit so that the voltage supplied to the tool remains more constant. In FIG4 , the electronic control unit 18 comprises a capacitor 50, which serves as an energy storage unit or accumulator. The downhole self-propelled cable tool 1 further comprises a machining tool 32 for performing machining operations and a compression joint 33, the compression joint 33 comprising a pressure measuring element 34 adjacent to the machining tool 32. In another embodiment, the electronic control unit 18 controls the controllable valves 16, 17, 26, 27 based on the current and/or voltage measured by the electronic control unit 18.

In FIG3 , each electric motor 4, 22 may further include a power or current limiting unit 31 so as to distribute a first portion of the current from the cable 5 to power the first electric motor 4 and a second portion of the current to power the second electric motor 22. The first and second downhole self-propelled cable tools 1, 1a, 1b may be electrically connected in parallel. The downhole self-propelled cable tool 1 may further include a current distribution unit 21 so as to distribute a first portion of the current from the cable 5 to power the first electric motor 4 and a second portion of the current to power the second electric motor 22. The current distribution unit 21 may be applied instead of the power limiting unit 31 so as to distribute a first portion of the current from the cable 5 to power the first electric motor 4 and a second portion of the current to power the second electric motor 22.

By having a power limiting unit, the power can be optimally distributed so that a first part of the current from the cable powers the first electric motor and a second part of the current powers the second electric motor. This enables a downhole self-propelled cable tool string having at least one pump per drive section to be driven without the first downhole self-propelled cable tool 1a and the second downhole self-propelled cable tool 1b becoming out of sync, so that one is driven faster than the other and thus acts as a "brake".

By providing an electric motor and pump for each drive section, the downhole self-propelled wireline tool string 1 can be driven at full speed as one drive section and have double the pulling force as two drive sections. The power curve of a known downhole tool string with one pump for driving two drive sections (e.g. 3kW) starts at the same maximum force as the power curve of a tool string with at least one pump per drive section, but the power curve of a downhole tool string with at least one pump per drive section (as shown in FIG8 ) extends to a point where the speed is twice that of the known downhole tool string. Therefore, at low speeds, the available pulling force is the same for the known tool string and the tool string of the present invention, but the downhole self-propelled wireline tool string 1 with at least one pump per drive section can be driven twice as fast at high speeds as the known tool string with only one pump for driving two drive sections. This is because the pumped fluid does not have to pass through one drive section to be delivered to the next drive section, so no energy is wasted in the transition from one drive section to the next. By having one pump for one drive section, the diameter of the fluid passage in the drive section can be larger than when the pump has to provide fluid to more than one drive section. The overall diameter of the tool string 1 is limited by the well, so the pump is usually a limiting factor, as a larger diameter is required for greater pumping capacity. By having only one drive section, the pumping force is used directly, and the fluid passage can be made larger, for which reason the limited current in the cable is used more efficiently than in known tool strings where several drive sections are driven by one pump.

In FIG4 , the downhole self-propelled cable tool 1 is a user interface 36 on the surface 37 for controlling at least a portion of the downhole self-propelled cable tool 1. Thus, the field engineer can be informed of the current limit of the cable/cable and set the current limit of each motor of the tool through the user interface, and the power limiting unit 31 or current distribution unit 21 distributes the current equally between the first downhole self-propelled cable tool 1a and the second downhole self-propelled cable tool 1b forming the tool 1, so that both can be driven at the same speed and thus drive the tool string at the same speed. In order to drive the tool string at the same speed, the first electric motor 4 may require more power than the second electric motor 22, but this is possible because the first and second downhole self-propelled cable tools 1, 1a, 1b are electrically connected in parallel. Although not shown, the downhole self-propelled cable tool string may also include a stroke tool.

A stroke tool is a tool for providing an axial force. The stroke tool comprises an electric motor for driving a pump. The pump pumps fluid into a piston housing to cause a piston to act in the piston housing. The piston is arranged on a stroke rod. The pump can pump fluid into the piston housing on one side and simultaneously suck out fluid on the other side of the piston.

"Fluid" or "wellbore fluid" refers to any type of fluid present downhole in an oil or gas well, such as natural gas, petroleum, oil-based mud, crude oil, water, etc. "Gas" refers to any type of gas component present in a well, a completed well, or an open hole, and "oil" refers to any type of oil component, such as crude oil, oil-containing fluids, etc. Gas, oil, and water fluids may therefore each include other elements or substances in addition to gas, oil, and/or water, respectively.

"Casing" or "metal well casing" means any type of pipe, tubing, tubular structure, liner, tubular string, etc. used downhole in connection with oil or natural gas production.

Although the invention has been described above in conjunction with preferred embodiments thereof, it will be apparent to a person skilled in the art that several modifications are conceivable without departing from the invention as defined in the following claims.

Claims (17)

1. A method (100) for controlling a tool string having a downhole self-propelled wireline tool (1) with wheels (8) rotated by hydraulic means and connected to a projectable arm assembly (6) projectable by the hydraulic means, the method comprising:

-running (110) a downhole self-propelled wireline tool (1) into a borehole (2), the downhole self-propelled wireline tool being connected to a second end (47) of a wireline (5), the first end of the wireline being connected to a power source, the downhole self-propelled wireline tool having a tool body (3) and a plurality of wheels (8) rotatable by means of hydraulic means, each wheel being connected to a projectable arm assembly (6) projectable from the tool body by means of hydraulic fluid from a first hydraulic pump (12), the downhole self-propelled wireline tool having an electric motor (4) rotatable at an operating rotational speed for driving the first pump,

-Defining a maximum allowable electrical power usage of the cable tool (1);

-supplying (120) electrical power to the downhole self-propelled wireline tool to run the downhole self-propelled wireline tool at a first speed, thereby forcing the downhole self-propelled wireline tool through the wellbore with a first force;

-determining a first maximum allowable operating speed of the electric motor based on a maximum allowable electric power usage at a first predetermined motor output torque of the electric motor;

-determining (130) a motor output torque of the electric motor; and

Comparing whether the operating speed exceeds a maximum allowable operating speed of the electric motor at the determined motor output torque,

Wherein the method further comprises adjusting (160) the operating speed of the electric motor based on the result of the comparison, so as to adjust the first speed to the second speed when the operating speed is higher than a maximum allowed motor speed.

2. The method of claim 1, wherein the method further comprises determining a second maximum allowable operating speed of the electric motor based on a maximum allowable amount of electric power at a second predetermined motor output torque of the electric motor.

3. The method of claim 1, wherein the method further comprises determining a third, fourth, or subsequent maximum allowable operating speed of the electric motor based on a maximum allowable electric power usage at a third, fourth, or subsequent predetermined motor output torque of the electric motor.

4. A method according to any of the preceding claims, wherein adjusting the operating speed of the electric motor based on the result of the comparison is performed independently of any condition of the cable, such as the pulling force in the cable, the cable tension or the cable resistance.

5. A method according to any of the preceding claims, wherein adjusting the operating speed of the electric motor based on the result of the comparison is performed independently of any pump conditions, such as pump flow, pump pressure or stroke length.

6. A method according to any of the preceding claims, wherein adjusting the operating speed of the electric motor based on the result of the comparison is performed independently of any representation of the speed of the downhole self-propelled wireline tool.

7. A method according to any preceding claim, wherein the first speed of the downhole self-propelled wireline tool is adjusted to a second speed by adjusting the operating speed of the electric motor.

8. The method of any of the preceding claims, further comprising determining (145) an operating speed of the electric motor.

9. The method according to any of the preceding claims, wherein determining the output torque of the electric motor is performed by measuring (125) currents on three phases in the electric motor.

10. The method according to any of the preceding claims, further comprising measuring (135) a current demand/input of the electric motor and measuring (135 b) a voltage input of the electric motor.

11. The method according to any of the preceding claims, wherein determining (140) a maximum allowable motor speed based on the motor output torque is further based on the measured current and the measured voltage of the electric motor.

12. The method according to any one of claims 1-9, wherein the adjustment (160 a) of the operating speed of the electric motor is based on a measured current demand of the electric motor or a calculated load of the electric motor.

13. A method according to any one of the preceding claims, wherein each wheel comprises a hydraulic motor (10) for rotating the wheel by means of a second fluid having a second fluid pressure and each wheel provides a self-propelling movement, each wheel being connected with a second arm end (11) of one of the projectable arm assemblies, the plurality of projectable arm assemblies (6) being movably connected with the tool body at a first arm end (7) and being projectable from the tool body by means of a first fluid having a first fluid pressure, the downhole self-propelled cable tool further comprising a pressure sensor measuring (130 d) the second fluid pressure.

14. The method of claim 13, wherein each hydraulic motor is driven by a second fluid having a second fluid pressure from the first hydraulic pump or from a second hydraulic pump driven by the electric motor.

15. The method according to claim 14, wherein the adjustment (160 c) of the rotational speed of the electric motor is based on the second fluid pressure.

16. The method according to any of claims 13-15, further comprising controlling (170) the first fluid pressure based on a second pressure by means of a first controllable valve (16) in a hydraulic section (15) of the downhole self-propelled wireline tool.

17. A hydraulically driven downhole self-propelled wireline tool configured to perform the method according to any of the preceding claims.