Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
2002-04-16
2004-04-13
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S228000, C324S207200, C324S207210, C324S207240, C324S262000, C166S255100, C166S066500
Reexamination Certificate
active
06720764
ABSTRACT:
BACKGROUND OF THE INVENTION
In oil and gas wells, jointed pipes are conventionally inserted and stripped from a well bore under pressure. The intermittent sections that comprise the jointed pipes are typically connected by tool joints, which are generally threaded end connections.
In standard operations, the jointed pipes are moved in or out of the well bore through blow out preventers (BOPs). The mounting and operation of BOPs are well known in the art. Typically, two BOPs are mounted on a spool (a “BOP spool”), with one BOP at the upper end of the spool and the other BOP at the lower end of the spool. The BOPs operate to separate the high pressure of the well bore from atmospheric pressure. Each BOP comprises a hydraulic ram that seals around the outside diameter of the pipe to pressure seal the well bore. The upper ram is normally kept closed when a pipe is stripped from the well. Because the BOP rams seal around the outside diameter of the piping, any reasonable increase in size of the piping may damage the rams and piping and may also compromise the sealing capabilities of the rams.
As a tool joint enters the bottom of the spool during stripping, the upper ram is closed, and the lower ram is open. When the tool joint clears the lower ram, the stripping of the pipe is temporarily suspended. The lower ram is then closed, and the spool is depressurized to atmospheric pressure. After depressurization, the upper ram is opened, and the stripping of the piping is resumed until the tool joint exits the upper BOP ram. The upper ram is then closed, and the spool is re-pressurized to the pressure of the well bore. After re-pressurization, the lower ram is opened, and the procedure is repeated upon entry of the next tool joint into the bottom of the spool. When jointed pipe is moved into the well instead of stripped from the well, the same procedures apply in clearing the tool joints of the BOPs but in the opposite order.
The movement of the tool joints through BOP spools is known to present operational problems. The rig operator is generally unable to see the tool joint enter the BOP spool. When a tool joint enters the BOP spool, if the operator does not stop the movement of the tool joint and properly open the closed BOP ram, the tool joint may contact the closed BOP ram, which may cause damage to the tool joint or BOP. If the damage is serious, the rig safety may be compromised, and a well blowout could occur. To prevent this occurrence, rig operators have historically estimated pipe lengths, and have then tallied pipe lengths between the joints to facilitate location of each tool joint as it enters the BOP spool. Errors in calculations or by the operator may cause the tool joint to strike a closed BOP ram. Further drawbacks of this process include the lack of speed at which the operator must work to prevent any such slight errors that may damage the BOP ram or tool joint.
In addition to jointed pipes, coiled tubing strings are conventionally inserted and stripped from a well bore under pressure, which also presents operational problems. In standard operations, the coiled tubing string is typically moved in or out of the well bore through a crown valve and a BOP stack. The crown valve is generally the top valve on the arrangement of pipes, valves and instruments typically found at the surface of a well bore, known colloquially as the “Christmas tree.” The BOP stack may have a plurality of BOPs comprising at least one stripping BOP, which is different than the upper and lower BOP configuration that is standard for the jointed pipe operations.
As the coiled tubing string is stripped from the well bore, the crown valve is open and the stripping BOPs are closed. When the last of the coiled tubing string exits the crown valve and begins to enter the BOP stack, the crown valve must be closed to maintain the well pressure. If the crown valve is not closed, the well would be open to the atmosphere and thereby increase safety and environmental risks and exposures. To prevent this occurrence, historically a friction counter will be used to estimate the coiled tubing string length. Coil tubing personnel will mechanically operate the crown valve by carefully attempting to close the crown valve to identify when the coiled tubing string exits the crown valve. Errors in calculations by the friction counter and by the coil tubing personnel may result in flooding of the well. Further drawbacks also include the lack of speed at which the operator must work to prevent any such slight errors that may cause safety and environmental exposures.
Therefore, it is highly advantageous to correctly locate tool joints in the BOP spool and to correctly locate the last of the coiled tubing string to exit the crown valve. It will be understood that the presence of a pipe (for example a coiled tubing string) in a spool will cause a deviation in a magnetic field exerted across the spool. Because tool joints have larger outside diameter and mass than the pipe, the tool joints cause an even greater deviation in the magnetic field. Consequently, magnetic locators have been used in the past to identify the location of the tool joints and the presence of the coiled tubing string. For instance, magnetic sensors such as gradiometers have been used to identify the presence of tool joints in the BOP spool by sensing a change in the earth's magnetic field due to the presence of a tool joint. Problems encountered with this technology include interference from surrounding ferrous objects that may lead to false joint identification. Further, in deployments near the equator, it will be appreciated that readings of the earth's magnetic field tend towards zero, making it extremely difficult for magnetic sensors to identify the magnetic flux change due to the presence of a tool joint or the last of a coiled tubing string.
Besides identifying changes in the earth's magnetic field to locate a tool joint or identify the presence of a coiled tubing string, the prior art has also utilized electromagnets to identify piping. One such device is disclosed in U.S. Pat. No. 4,964,462. In the disclosure of this patent, a magnetic field is created by electromagnets attached to a nonmagnetic BOP spool that separates upper and lower BOPs. Sensors mounted on the nonmagnetic spool identify changes in the electromagnetic field that signify the presence of a tool joint. Improvements need to be made on using electromagnets in a well bore, whose operation requires potentially unsafe voltages and currents to be deployed down hole.
Consequently, there is a need for an improved method for inserting and stripping jointed pipes and coiled tubing strings from a well bore. Further, there is a need for a more safe and effective way of identifying tool joints in a BOP spool and identifying the presence of a coiled tubing string in a spool.
SUMMARY OF THE INVENTION
These and other needs in the art are addressed in one embodiment by an inventive method for detecting ferrous changes passing axially through a cylindrical space. The method comprises surrounding the cylindrical space with a nonmagnetic cylinder having an outer wall and a cylindrical axis; creating an alternating magnetic field in the cylindrical space, the magnetic field created by a rotatable permanent magnet; monitoring the magnetic field with magnetic flux sensors placed outside the outer walls; and detecting changes in the magnetic field as ferrous matter passes axially through the cylindrical space.
In another embodiment, the invention comprises an apparatus that identifies ferrous changes as a tool joint in a jointed tubing string with the tubing string moving in and out of a well bore and a plurality of the tool joints connecting sections of the jointed tubing string. The apparatus comprises a nonmagnetic cylindrical spool having a cylindrical axis, the tubing string and tool joints disposed to move axially in or out of the nonmagnetic cylindrical spool; and a sensor device attached to the nonmagnetic cylindrical spool, the sensor device having a source piece and at least one
Burrington John S.
Falcon Jonathan J.
MacInnis Jason P.
Relton Mahendran S.
Thomas Energy Services Inc.
Vinson & Elkins L.L.P.
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