GB2306657A

GB2306657A - Wellhead tool detector

Info

Publication number: GB2306657A
Application number: GB9521698A
Authority: GB
Inventors: Tuijl Bert Van
Original assignee: TUIJL BERT VAN
Current assignee: TUIJL BERT VAN
Priority date: 1995-10-18
Filing date: 1995-10-18
Publication date: 1997-05-07
Anticipated expiration: 2015-10-18
Also published as: GB9521698D0; GB2306657B

Abstract

A system for use in a borehole (e.g. a gas or oilwell) for detecting the position of a tool on a wireline 22 comprises at least one sensor 24, such as a coil, magnetoresistive element or Hall effect device, affixed to an external surface of the wellhead and arranged to detect the passage of a marker associated with the tool. The marker may be a magnetic element secured to the tool or may be an integral part of the tool. A signal from the sensor or sensors may be used to automatically switch off a winch 23 when the presence of the tool at the wellhead is detected.

Description

A DETECTOR This invention relates to a detector for detecting the presence of a tool or other element in an oil or gas well installation. The detector of the invention is particularly, though not exclusively, suitable for detecting the presence of a tool or designated element in an enclosed region at a remote location of, for example, an oil or gas well installation.

In the extraction of well fluids from underground reservoirs, various tools are lowered into the drill string or annulus of an oil or gas well installation. These tools might be devices for controlling the circulation of well fluid, for testing well fluids or formations, for extracting or removing obstructions, or for pumping fluid to the surface when well pressures do not provide adequate fluid flow. Tools are generally lowered on a wire or coiled tube into the well and these techniques are commonly known as wire line or coiled tubing operations. As well fluids can be under immense pressure, the tools may be inserted into a well using pressure control equipment. This ensures minimum risk of loss of pressure.

Once the tool has been used it is brought to the surface and removed. However, with existing techniques it is not easy to accurately determine the position of a tool within a well.

It is also necessary to keep an accurate record of the length of wireline or coiled tubing which has been lowered into the well. The tool is usually returned to a well lubricator and it is difficult to know whether the tool has been withdrawn into the well lubricator until it is pulled up into the top of the lubricator. However, this technique risks causing undue strain on the wireline or coiled tubing. It is not uncommon for the wireline to break causing subsequent loss of the tool and loss of pressure seal. A safety valve is installed to prevent loss of seal when this happens, but pressure testing of this valve cannot be done with equipment installed on the well. Loss of a tool can be particularly inconvenient as it results in down time and loss of produced well fluids while a further tool is lowered into the well to capture the lost tool.

The detector of the invention comprises sensing means which enable an operator to determine the position of a tool within an oil or gas production installation reducing the risk of tool loss or inaccurate positioning. The detector also enables longer tool strings to be introduced into the well precisely and efficiently.

According to the invention there is provided a detector for detecting the presence of an element in an oil or gas well and which comprises; a marker which in use is adapted to be secured in position relative to the element; one or more sensors adapted to produce an output signal in response to the presence of the marker; an interface for processing the output signal or signals, and an indicator connected to the interface for providing an indication of the presence of a marker.

The element may comprise or be attached to a tool, linking element (such as a deployment bar), or the wireline attached to the tool or element.

The marker may be a separate component which is adapted to be secured to the element, tool or wireline in use.

Alternatively, the marker may be formed by an existing part or component which is of such a type e.g. magnetic (for instance a motor in a tool) that its presence can be detected by the particular sensor which is employed.

Where the element is a linking element, such as a deployment bar, the marker could be built in during production.

The marker may also be formed by a "casing collar locator", or may be applied to a usual "rope socket".

The detector of the invention has the advantage that it can detect the presence of a downhole element or tool without making contact with the element, wireline, coiled tubing or the tool. This has the further advantage that the system does not wear out through frictional contact and can be isolated from the well fluids which can contain corrosive or flammable substances. Furthermore, well operators can switch off a winch OnCd the element or tool has been raised into the well lubricator. The detector can also be used with tool deployment bars which require exact tool string location. Such precise location of deployment bars is important in effecting sealing.

Preferably, the marker generates a magnetic field which can be detected by the sensor. Contact between the marker and sensor is not required and the magnetic field can be generated effectively and cheaply with, for example, a permanent magnet or electromagnet.

The marker may include a connector adapted to secure the marker to a tool, element, wireline or coiled tubing.

The marker may comprise a separate tool which can be connected intermediate of the downhole tool and wireline.

Preferably, the sensor is a magnetic field sensor. An example of a magnetic field sensor is an induction loop or coil, or more preferably "magnets-resistive" sensors may be used. A further example of a sensor is a hall effect device.

Two or more sensors may be provided. In this way additional information can be obtained about the position of the marker or markers. Two markers having the same spacing as a pair of sensors form a particularly preferred embodiment of the invention.

The interface may comprise a wheatstone bridge circuit connected to an amplifier to amplify the output signal. The wheatstone bridge circuit has the advantage that it is sensitive and can be easily adjusted for a balanced no output condition in the absence of a marker. Furthermore, the circuit is arranged so that any variation in the supply voltage does not produce a false alarm.

The amplifier may be a comparator. Use of a comparator provides a large output in response to a small change in the output signal from the sensor.

Preferably, barriers are provided which isolate the apparatus. This allows the detector to be used in hazardous environments without the need to obtain further certification before the tool is installed.

Preferably, the indicator produces an audible signal. An example of a suitable audible indicator is a loudspeaker or bell alarm.

The indicator may produce a visual indication. An example of a suitable visual indicator is a lamp or light emitting diode.

The interface may control a switch for switching off a winch system in response to detection of a marker. This construction of detector provides automatic switching off of the winch and has the advantage that the apparatus does not need to be continuously monitored. Examples of suitable switches include a solenoid or relay.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic drawing of a detector according to a first embodiment of the invention; Figure 2 is a schematic drawing of the detector of the first embodiment installed on an oil or gas production installation; Figure 3 is a schematic drawing of the interface and indicator; and Figure 4 is a schematic drawing of the detector of a second embodiment installed on a gas or oil production installation: Referring to the drawings Figure 1 depicts a tool detector in accordance with the invention, generally indicated by reference numeral 1, which comprises a sensor 2 connected to a length of cable 3 to provide a path for the output signal from the sensor to an interface and indicator assembly 4. The system can be permanently installed on the oil or gas production installation or it can be removed for use at another location.

The sensor comprises a suitable magnetic field sensor such as an induction loop, induction coil or hall effect device. However, it must be understood that other suitable magnetic field sensors known to the skilled man could also be used. The sensor produces an output signal in response to detection of a magnetic field produced by a tool marker connected to a downhole tool or to the wireline. This signal is processed by the interface and causes the indicator to provide a visual or audible signal. Examples of suitable indicators include loudspeaker, alarm bell or a lamp.

Figure 2 shows the tool detector installed on an oil or gas production installation comprising a well 20, winch 21 for lowering or lifting a downhole tool (not shown) on a wireline 22. The winch is controlled from a remote location such as a control room 23. The sensor 24 is fixed to an external surface of the well head in order to provide an output signal when a tool marker fixed to the tool or wireline is raised into the section 25. On detection of the tool marker an output signal is generated by the sensor and this in turn activates the indicator in the control room 23. An operator in the control room has an accurate position of the tool within the well and can stop the winch 21 before the tool is brought up against the lubricator.

The tool detector may be arranged to activate a solenoid or relay which automatically shuts down the winch when the tool is detected. This ensures that the tool cannot be raised passed the sensor and cause damage to the well.

Figure 3 5 a schematic diagram of the sensor, interface and indicator. The sensor 30 is incorporated in a wheatstone bridge circuit 31 which has its own d.c power supply 32. The d.c power supply is a low voltage supply and operates on five volts. Such a low voltage system has the benefit that any accident which causes a short circuit will not generate any sparks which could, in a hazardous environment, cause an explosion. The circuit 31 is connected to a comparator 33 with means 34 for adJusting the gain and a control 35 for adjusting the offset of the device. The gain of the comparator can be adjusted to obtain a desired level of sensitivity. An indicator 36 includes a meter 37 and loudspeaker 38 for providing a visual and audible signal when a tool marker is activated.Push button switches 39 are provided for setting and resetting the tool.

Safety barriers 40 are provided to isolate the circuits and power supply from the outside environment and provides additional protection in particularly hazardous environments.

Figure 4 illustrates an alternative embodiment of the invention which in addition to detecting a marker on a tool, is particularly suited to accurately monitoring the position of a deployment bar.

Deployment bars allow longer tool strings to be introduced to live wells, particularly where available height is limited which limits the length of lubricator sections available for making up the tool string.

The system works by introducing a tool string with a deployment bar rigged on its top end into a lubricator section.

A sealing valve, normally of the B.O.P type, is provided which can then be closed around the deployment bar to effect a seal.

Once sealed the lubricator section can be broken down and a further tool string attached to the deployment bar. Reassembly of the lubricator section allows the valve to be released and the extended tool string to be run into the well.

The process can be repeated to further extend the tool string if necessary.

Of vital importance is the accurate positioning of the deployment bar relative to the valve to give a full seal. Such positioning is difficult, particularly during down rigging as the string returns to the surface.

By providing a marker in a fixed position relative to the deployment bar the deployment bar's position in the lubricator section and hence relative to the valve can accurately be determined and controlled, thereby eliminating guess work.

Whilst the single sensor of the first embodiment is sufficient to determine position the use of two sensors 24a, 24b, Figure 4, provides more accurate locating information, By spacing the markers, preferably magnetic ones, in relation to the deployment bar by the same spacing as the two sensors on the section 25 a signal from both sensors very precisely locates the bar. Effective sealing can then be undertaken, particularly where one sensor is above and one sensor is below the valve 30.

Signalling of the position and detection of the markers can be effected using the system of Figure 3 duplicated for the second sensor.

The passage of the upper marker past the lower sensor on raising, vice versa on lowering, can be used as a warning of position approach and may lead to a signal in itself and/or give rise to automatic slowing of the system.

It may not be necessary to use a tool marker when the tool detector is used in conjunction with downhole tools which contain a permanent magnet, for example, downhole motors, electric submersible pumps and remote sensing apparatus.

The detection operation may be carried out in the vicinity of a usual "lubrication unit" above a Christmas tree.

Claims

CLAIMS:

1. A detector for detecting the presence of an element in an oil or gas well and which comprises; a marker which in use is adapted to be secured in position relative to the element; one or more sensors adapted to produce an output signal in response to the presence of the marker; an interface for processing the output signal or signals, and an indicator connected to the interface for providing an indication of the presence of a marker.

2. A detector according to claim 1 in which the element comprises or is attached to a tool, linking element, a deployment bar, or the wireline attached to the tool or element.

3. A detector according to claim 1 or claim 2 in which the marker is a separate component which is adapted to be secured to the element, tool or wireline in use.

4. A detector according to claim 1 or claim 2 in which the marker is formed by an existing part or component which is of such a type that its presence can be detected by the sensor employed.

5. A detector according to any preceding claim in which the marker generates a magnetic field which can be detected by the sensor.

6. A detector according to any preceding claim in which the sensor is a magnetic field sensor such as an induction loop or coil, or magnets-resistive sensors or a hall effect device.

7. A detector according to any preceding claim in which two or more sensors are provided.

8. A detector according to claim 7 in which two markers having the same spacing as a pair of sensors are provided.

9. A detector according to any preceding claims in which the interface comprises a wheatstone bridge circuit connected to an amplifier to amplify the output signal.

10. A detector according to any preceding claim in which the amplifier is a comparator.

11. A detector according to any preceding claim in which the indicator produces an audible signal.

12. A detector according to any preceding claim in which the indicator produces a visual indication.

13. A detector according to any preceding claim in which the interface controls a switch for switching off a winch system in response to detection of a marker.

14. A detector according to claim 7 or any claims depending therefrom in which one sensor is above and one sensor is below a valve.

15. A detector according to claim 7 or any claims depending therefrom in which the passage of the upper marker past the lower sensor on raising can be used as a warning of position approach and may lead to a signal in itself and/or give rise to automatic slowing of the system.