Coding system for use in a wellbore

Abstract

 A coding system for use in a wellbore formed in an earth formation is provided. The system comprises a tubular conduit (3) extending in the wellbore and being provided with at least one transmitter array, each transmitter array being arranged at a selected wellbore location and including at least one transmitter arranged in a selected pattern representative for said location. Each transmitter induces a field selected from a magnetic field and an electromagnetic field into the interior of the conduit. Further is provided a sensor (30) suitable to be lowered through the conduit and to interact with each field, and means for generating a signal representative of the interaction of the sensor with each field.

Description

[0001] The present invention relates to a coding system for use in a wellbore formed in an earth formation. It is common practice to lower wellbore tools or equipment through a conduit extending into the wellbore for a variety of purposes, the conduit being, for example a wellbore casing extending from surface to a reservoir zone of the earth formation. The tools or equipment generally are to be lowered to a selected depth at which a dedicated function is to performed, e.g. drilling of a branch borehole, setting of packers, etc. In case of a multilateral wellbore having a main wellbore and one or more branch wellbores, selective access to the branch wellbores is generally required, implying that identification of the position of the connections of the branch wellbores to the main wellbore is required. In each such application it is important that the tool or equipment is accurately positioned at the required depth. One way of identifying a selected wellbore depth is to provide dimensional changes to the casing at the selected depth, for example a section of reduced diameter through which a specific wellbore component cannot pass. However, such diameter changes reduce the wellbore diameter. In case of a multilateral wellbore the change of diameter at each branch connection results in a wellbore having a lower part of unacceptably diameter reduction.

[0002] It is an object of the invention to provide an adequate coding system for use in a wellbore, which overcomes the problems inherent to coding by dimensional changes.

[0003] In accordance with the invention there is provided a coding system for use in a wellbore formed in an earth formation, comprising a tubular conduit extending in the wellbore and being provided with at least one transmitter array, each transmitter array being arranged at a selected wellbore location and including at least one transmitter arranged in a selected pattern representative for said location, each transmitter inducing a field selected from a magnetic field and an electromagnetic field into the interior of the conduit, a sensor suitable to be lowered through the conduit and to interact with each field, and means for generating a signal representative of the interaction of the sensor with each field.

[0004] The transmitters are arranged in a pattern unique to the location of the array, therefore the induced fields form a pattern of fields also unique to the location. Since the sensor interacts with each field, the interaction of the sensor with the pattern of fields, and the produced signal, also are unique to the location so that the array pattern can be identified. The depth location is then inferred from the unique relationship between the array pattern and the depth location.

[0005] In a preferred embodiment the wellbore is a multilateral wellbore including a main wellbore and at least one branch wellbore extending from a branch point of the main wellbore, said transmitter array being located substantially at said branch point. The depth location of the branch points can thereby be inferred without the need for dimensional changes at the branch points. The invention will be described hereinafter in more detail and by way of example with reference to the accompanying drawings in which:

Fig. 1 schematically shows a longitudinal cross-section of a wellbore casing applied in an embodiment of the coding system of the invention;

Fig. 2 schematically shows cross-section 2-2 of Fig. 1;

Fig. 3 schematically shows a longitudinal side view of a sensor tool applied in the embodiment relating to Fig. 1; and

Fig. 4 schematically shows cross-section 4-4 of Fig. 3.

[0006] Referring to Figs. 1 and 2 there is shown a section 1 of a tubular wellbore casing 3 extending in a wellbore (not shown) formed in an earth formation (not shown). The casing section 1 is made of non-magnetic metal, for example ....... The outer surface of the casing section 1 is provided with four recesses 5, 7, 9, 11 arranged at substantially equal depth and at selected mutual angular intervals α₁, α₂, α₃, α₄ relative to the longitudinal axis 12 of the casing 3. The intervals α₁, α₂, α₃, α₄ are uniquely related to said depth. The recesses 5, 7, 9, 11 are provided with an array of transmitters in the form of permanent magnets, 14, 16, 18, 20 locked into the recesses by locking member 22, 24, 26, 28. Thus, magnet 14 is arranged in recess 5 and locked by locking member 22, magnet 16 is arranged in recess 7 and locked by locking member 24, magnet 18 is arranged in recess 9 and locked by locking member 26, and magnet 20 is arranged in recess 11 and locked by locking member 28. Similar to the arrangement of the recesses, the magnets are arranged at mutual angular intervals α₁, α₂, α₃, α₄ relative to the longitudinal axis 12. Although the magnets 16, 18, 20 are not visible in the cross-section of Fig. 1, their position has been indicated in dotted lines for the purpose of clarity. Each magnet 14, 16, 18, 20 induces a magnetic field (not shown) into the interior of the casing section 1.

[0007] Referring further to Figs. 3 and 4 there is shown a sensor tool 30 supported by wire line 32 from a control facility (not shown) at surface. The tool 30 is provided with a plurality of electric circuits (not shown), each circuit including an electric relay 34 arranged to actuate a change in the circuit upon entering the magnetic field induced by one of the magnets 14, 16, 18, 20. The relays are arranged at regular angular intervals along the outer circumference of the tool 30. Each circuit is in electric contact with the control facility via an electric conductor (not shown) extending along the wireline 32. The control facility is capable of receiving a signal from each circuit indicating said change of the circuit.

[0008] During normal operation the sensor tool 30 is lowered from surface into the casing 3. When the tool 30 arrives at the location of the magnets 14, 16, 18, 20, each magnet will be in close proximity of one of the relays 34. As a result four of the relays 34 enter the magnetic fields induced by the magnets, said four relays being located at mutual angular intervals α₁, α₂, α₃, α₄ relative to the longitudinal axis (not shown) of the tool. Each one of the four relays thereby actuates a change in the corresponding circuit, resulting in a corresponding signal being transmitted from the circuit through the electric conductor to the control facility at surface. From the four signals being received at the control facility the mutual angular intervals α₁, α₂, α₃, α₄ of the four relays are deduced. The depth of the tool 30 in the wellbore is then determined from the unique relationship between the angular intervals α₁, α₂, α₃, α₄ and the depth of the magnets 14, 16, 18, 20 in the wellbore.

Claims

1. A coding system for use in a wellbore formed in an earth formation, comprising a tubular conduit extending in the wellbore and being provided with at least one transmitter array, each transmitter array being arranged at a selected wellbore location and including at least one transmitter arranged in a selected pattern representative for said location, each transmitter inducing a field selected from a magnetic field and an electromagnetic field into the interior of the conduit, a sensor suitable to be lowered through the conduit and to interact with each field, and means for generating a signal representative of the interaction of the sensor with each field.

2. The coding system of claim 1, wherein each transmitter array includes a plurality of transmitters arranged at substantially equal depth in the wellbore and at selected mutual angular orientations around the wellbore axis.

3. The coding system of claim 1 or 2, wherein each transmitter induces a magnetic field in the interior of the wellbore.

4. The coding system of claim 3, wherein transmitter is a permanent magnet.

5. The coding system of claim 2 or 3, wherein the tubular conduit is made of a non-magnetic material.

6. The coding system of any one of claims 3-5, wherein the sensor includes a plurality of electric circuits, each circuit including an electric relay actuating a change in the circuit upon entering the magnetic field.

7. The coding system of any one of claims 1-6, wherein the tubular conduit is a casing of the wellbore.

8. The coding system of any one of claims 1-7, wherein the wellbore is a multilateral wellbore including a main wellbore and at least one branch wellbore extending from a branch point of the main wellbore, said transmitter array being located substantially at said branch point.

9. The coding system substantially as described hereinbefore with reference to the drawings.

Drawing