WO2000034622A1

WO2000034622A1 - Downhole tool detection means

Info

Publication number: WO2000034622A1
Application number: PCT/GB1999/004148
Authority: WO
Inventors: Dave Mcdonald
Original assignee: INTERVENTION WELL SYSTEMS Ltd
Current assignee: INTERVENTION WELL SYSTEMS Ltd
Priority date: 1998-12-09
Filing date: 1999-12-09
Publication date: 2000-06-15
Anticipated expiration: 2001-06-09
Also published as: GB9827059D0; AU1669700A

Abstract

The present invention relates to apparatus adapted to detect and indicate the position of downhole tools as they enter and exit the well. A magnetic sensor (21) mounted on a bracelet (20) is fixed to the neck of a surface valve (14) and operates to activate an alarm on detecting the presence of magnets (9) on an indicator sub (1) as it passes the sensor (21). The operator is thus provided with an accurate indication that the toolstring has been retrieved.

Description

DO NHOLE TOOL DETECTION MEANS

This invention relates to a downhole tool detection means. In particular, it relates to a means for determining when a tool in a well is near the surface valve.

Within the oil and gas industry there is a frequent need to enter wells with various methods of intervention. These workovers can be achieved by various techniques including wireline, slickline, electric line or coiled tubing. In each of these techniques the well is entered via a safety barrier valve which is located on top of the surface wellhead. In the event of a dangerous increase in well pressure, the valve closes and shears through the line or coil, sealing and holding well pressure. Prior to well intervention by whichever method, the rig up above the valve is completed. This rig up is also pressure retaining, so that pressure is retained when the valve is opened to allow well intervention.

Once the valve is opened, the tool is lowered through the valve and down into the well. The progress of the tool is monitored via a depth indicator. Due to the high value of production from an individual well, it is important to perform all workovers quickly. As a well may typically be 30,000 feet deep it is clear that it is desirable to lower and retrieve tools at high velocities.

Due to the high velocity of tool retrieval, whenever a tool is removed, the depth indicator is monitored closely. Should an error be made and that tool slam into the top of the rig, detach and fall down the well, the resultant fishing operation is time consuming and therefore very expensive due to the concomitant lost production.

A common approach to depth indication during wireline operations involves the use of a calibrated tangential wheel or sheave at the surface. This allows measurement of the length of wire in the well and therefore the depth of the tool. Unfortunately, this technique is not sufficiently accurate. For example, the circumference of the wheel may vary due to mud or ice build-up; the wheel may slip relative to the wire; the wire will stretch by an unpredictable amount from the weight of the tool and from the unpredictable stresses when the tool collides with or snags on the edge of the well; furthermore, the dimensions of the wheel and the wire both vary with temperature. Given the great length of wire involved, even proportionately small errors lead to substantial uncertainty in the location of the tool. As a result of this uncertainty, great care must be taken not to overrun the tool or else costly accidents occur.

The prior art has concentrated on developing ways of reducing or correcting for these uncertainties or on devising other means of depth indication. However, depth indication remains inaccurate, slowing down interventions and causing occasional very expensive accidents.

It would be advantageous to provide a downhole tool detection means which indicated when the downhole tool was close to the surface valve, alerting the operator or engaging an automatic means to prevent the tool slamming into the top of the rig. Such a detection means would prevent overrun accidents. Furthermore, it may speed up the retrieval of downhole tools as less time would be wasted taking care to avoid overrun.

According to the present invention there is provided downhole tool retrieval detection apparatus comprising means on a surface assembly for detecting the presence of a tool assembly within the surface assembly.

Typically, the downhole tool retrieval detection means comprises a sensing means which is positioned on the well riser, near the surface valve.

Preferably the sensing means may be mounted on the outside of the well riser.

In particular, the sensing means comprises a sensor bracelet which is adapted to removably encircle and grip the well riser.

The downhole tool may be labelled by a tool indicator means characterized in some way which can be detected by the sensing means.

The indicator means may be adapted to be removably attached to a tool. The indicator means may be adapted to be removably incorporated into a toolstring.

The tool indicator means may be incorporated into a tool.

The tool indicator means may have distinguishing electromagnetic characteristics and the sensing means be adapted to recognise these characteristics.

For example, the tool indicator means may contain a magnet .

Alternatively, the tool indicator means may contain a plurality of magnets.

When the tool indicator means contains one or more magnets, the sensing means may be adapted to detect the resulting magnetic field when the tool indicator means passes the sensing means.

The sensing means may instead detect the changing magnetic field when the tool indicator means passes the sensor.

An example embodiment of the invention will now be described with reference to the following Figures, in which:

Figure 1 shows a cross-section through the indicator means and the components to which it is attached;

Figure 2 shows a well riser and surface valve fitted with a sensor bracelet; Figure 3 shows a cross-section through the riser and sensor bracelet along the line A-A of Fig 2;

Figure 4 shows a cross-section through the part of the system case where components are stored;

Figure 5 shows the top of the system case where various indicators are present;

Figure 6a shows a perspective view of a complete assembly incorporating downhole tool detection apparatus; and

Figure 6b is a perspective view to an enlarged scale of part of the apparatus of Figure 6a.

This example embodiment is based on a wireline operation but would apply exactly the same for slickline, electricline and coiled tubing operations.

All components of the downhole tool detection means are initially packed in a portable system case which contains both the controls for operation of the device and all other components which are required.

On arrival at the site an indicator sub 1 , as shown in Figure 1 , is removed from the system case and removably installed between the rope socket 2 and wireline tool 3 during wireline rig up. The indicator sub has an appropriate adapter 4, enabling it to be removably attached to a wireline tool via a quick latch 5. Similarly, removable attachment to the rope socket is facilitated by an adapter 6 and latch 7. As is common practice in the wireline industry, the indicator sub and standard wireline tools incorporate a fishing neck profile 8.

The indicator sub contains one or more permanent magnets 9 and is constructed from a material which is either non- magnetic or, if a magnetic material is used, is isolated from the permanent magnet (s).

Figure 2 shows a well riser 10 where the wellhead 11 joins the wellhead crossover 12 and wellhead adapter 13. A wireline surface valve 14 is shown in this example.

A sensor bracelet 20 is also removed from the case and installed around the neck of the wellhead adapter. Cable 15 is pulled from a reel in the sensor case, safely routed to the wellhead and then attached to the sensor bracelet .

Figure 3 shows a cross section through the wellhead adapter and sensor bracelet 20 along plane A-A. Electromagnetic sensor 21 is adapted to respond to the magnetic field due to the magnet (s) 9 of indicator sub 1 when they pass the sensor. It is incorporated into one or more sensor carrier (s) 22 which is manufactured from stainless steel and has slots through which strap 23 is passed. The sensor bracelet may well incorporate several sensor carriers and sensors, equally spaced around the circumference of the wellhead adapter. The base of the sensor carrier (s), where they sit on the neck of the wellhead adapter, are shaped in such a way as to sit firmly on various diameters of wellhead adapter. Strap 23 is manufactured from flexible strip material such as stainless steel or kevlar. It incorporates a clasp and tightening mechanism which allows the sensor bracelet to be removably secured in position.

Figure 4 shows the system case 30 and figure 5 details an indicator panel 31 which is incorporated into the top of the case. The case is constructed of a robust, impact resistant but light-weight material suitable for transportation to offshore working locations and is adapted for rough handling. The case contains customised shaped galleries for storing the indicator sub 32 and the sensor bracelet 33. All loose components are stored within such galleries where they can be firmly secured and strapped in place to avoid the possibility of movement during transport. All equipment which is permanently installed within the case is secured with soft but resilient rubber mounts in such a way as to avoid impact damage. Any necessary hand tools are supplied and stored within the system case and are constructed from chrome vanadium steel.

The cable to attach the case to the sensor bracelet is stored on a reel 34. This cable reel has winding handles and rotates on a spindle which incorporates an electrical slip ring so that the cable can be pulled off the reel and electrical continuity will be maintained.

The case incorporates an EXD rated battery 35 and a battery charger 36. All electrical and electronic components are EXD rated due to the potentially explosive atmosphere around the wellhead. Once the wireline rig up has been completed and the sensor bracelet attached to the wellhead adapter, the device is switched on, activating a power on indicator 37. The valve is then opened and the wireline tool complete with indicator sub is lowered into the well. As the indicator sub passes the sensor bracelet and is detected, a visual indicator 38 and audio indicator 39 come on to show that the device is functioning correctly. At this stage, the reset button 40 is pressed which stops the visual and audio indicators. The unit then remains in this mode until the wireline tool is retrieved and is again detected by the sensor (s) whereupon the visual and audio indicators come on again, alerting the operator to the proximity of the wireline tool to the surface valve.

Clearly this device may readily be adapted to automatically stop or slow down the tool lifting gear.

With this invention, it is possible to accurately and reliably determine when a tool is close to the surface valve, without having to rely on the insufficiently accurate depth indicators currently available. This invention will therefore reduce accidents in which retrieved tools are overrun and hit the surface valve, the serious consequences of which were described above. This will not only prevent expensive accidents but may allow tools to be raised faster, reducing the time taken for interventions and so saving money.

A particular advantage of the present invention is that the sensing means may be attached to the outside of the well riser and therefore added or removed quickly and conveniently. In an alternative embodiment, the sensing means might also be incorporated in the wellhead adapter itself or another component of the riser.

Referring now to figures 6a and 6b a slightly re- configured but essentially similar embodiment is illustrated and like components are therefore accorded identical reference numerals.

The only significant difference on this embodiment is the addition of a remote visual indicator box 41 which is located in the operators cabin 42. The visual indicator box 41 carried two LED lights. A green light indicates system operational and a red light indicates the alarm activated. The lights are mounted so as to be in the operators line of vision to his other controls and thus avoids the need to glance away to look at the main indicator.

As described the system positively indicates the location of slickline, electricline and coiled tubing tools as they enter and exit the well. It allows operators to retrieve tools into the surface equipment in a controlled manned without having to compensate for depth counter slippage or line/pipe stretch.

Correct use of the system eliminates any risk of slamming tools into the seal head which may cause tool detachment and result in costly fishing operations and lost production. Independent safety case studies indicate a significant risk of fire and explosion due to hydrocarbon release to the atmosphere. Further modifications and improvements may be incorporated without departing from the scope of the invention herein intended.

Claims

Claims :

1. Downhole tool retrieval detection apparatus comprising means on a surface assembly for detecting the presence of a tool assembly within the surface assembly.

2. Downhole tool retrieval detection apparatus as claimed in Claim 1 wherein the downhole tool retrieval detection means comprises a sensing means which is positioned on the well riser, near the surface valve.

3. Downhole tool retrieval detection apparatus as claimed in Claim 2 wherein the sensing means is mounted on the outside of the well riser.

4. Downhole tool retrieval detection apparatus as claimed in Claim 3 wherein the sensing means comprises a sensor bracelet which is adapted to removably encircle and grip the well riser.

5. Downhole tool retrieval detection apparatus as claimed in any one of Claims 2 to 4 wherein the downhole tool is labelled by a tool indicator means adapted for detection by the sensing means.

6. Downhole tool retrieval detection apparatus as claimed in Claim 5 wherein the indicator means is adapted to be removably attached to a downhole tool.

7. Downhole tool retrieval detection apparatus as claimed in Claim 5 wherein the indicator means is adapted to be removably incorporated into a toolstring.

8. Downhole tool retrieval detection apparatus as claimed in any one of Claims 5 to 7 wherein the tool indicator means has distinguishing electromagnetic characteristics and the sensing means is adapted to recognise these characteristics.

9. Downhole tool retrieval detection apparatus as claimed in Claim 8 wherein the tool indicator means contains a magnet.

10. Downhole tool retrieval detection apparatus as claimed in Claim 9 wherein the sensing means is adapted to detect the resulting magnetic field when the tool indicator means passes the sensing means.