Magnetic sensor system useful for detecting tool joints in a downhold tubing string

#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.

#For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

#FIG. 1 illustrates one embodiment of a tool joint locator apparatus.

#FIG. 2 illustrates a view of the invention showing a housing, sensor, magnet, and motor.

#A first embodiment of the invention is described with respect to FIG. 1, in which a sensor device 5 comprises a source piece 10 and a sensor piece 15. The source piece 10 has a permanent magnet 20 and a source field shaper 25. The source field shaper 25 comprises a non-corrosive, soft magnetically permeable material, such as iron. Because the permanent magnet 20 exerts a magnetic field in all directions, the source field shaper 25 directs the magnetic field in the horizontal direction away from the source field shaper 25. As shown, the sensor piece 15 comprises sensors 30 and a sensor field shaper 35. The sensor field shaper 35 also comprises a non-corrosive, soft magnetically permeable material, again such as iron. The sensor field shaper 35 shields the sensors 30 from the effects of external magnetic fields such as the earth's magnetic field. A motor 40 is attached to the source piece 10 by a shaft 45.

#In the embodiment illustrated in FIG. 1, the source piece 10 is advantageously E-shaped, with three separate horizontal sections and a vertical section. The center horizontal section is the permanent magnet 20. The upper and lower horizontal sections and the vertical section comprise the source field shaper 25. The source piece 10 is horizontally rotatable 360 degrees by the motor 40 and shaft 45. The shaft 45 that connects the motor 40 to the source piece 10 is embedded into the vertical section of the source piece 10 and runs lengthwise down the vertical section. The motor 40 horizontally rotates the source piece 10 about the vertical axis of the shaft 45, thereby creating the alternating magnetic field.

#With further reference to FIG. 1, the sensor piece 15 is also advantageously E-shaped, with three separate horizontal sections and a vertical section. The upper and lower horizontal sections contain the sensors 30. The vertical section and the three horizontal sections comprise the sensor field shaper 35. A variety of sensor technologies known in the art may be used for the sensors 30 but preferably Hall effect sensors are used. Hall effect sensors are well known in the art. Examples of available Hall effect sensors include Honeywell SS 495A and Micronas HAL800 sensors. In the alternative, Anisotropic Magnetoresistive sensors or Giant Magnetoresistive sensors could be used for sensor technology instead of Hall effect devices. The center horizontal section serves as a return for the magnetic field, which helps shape the magnetic field. In addition to containing the sensors 30, the upper and lower horizontal sections also serve as conduit points for the return of the magnetic field thereby further helping shape the magnetic field.