Method of signaling passage of objects using tattle-tale apparatus
An electro-mechanical indicator system for signaling when a droppable object (such as, for example, a dart, plug or ball) is released during well cementing operations. A body section has first and second chambers divided by a fluid and pressure sealing barrier. A mechanical trigger mechanism is situated in the first chamber, which is exposed to elevated pressures and harsh wellbore fluids. Less robust components, such as sensor(s), power source(s), and signal device(s) located in the second chamber, remain isolated from the wellbore environment and elevated pressures.
1. A method for signaling passage of an object through a central flow bore of a tool comprising:
a. dropping an object through said central flow bore past an indicating device, wherein said indicating device comprises:
(i) a body member connected to said tool having a first chamber in pressure communication with said central flow bore, a second chamber at substantially atmospheric pressure, and a substantially solid and non-magnetic pressure sealing barrier disposed between said first and second chambers, wherein said barrier isolates said first and second chambers from each other;
(ii) a trigger pivotally mounted within said first chamber, wherein said trigger does not extend beyond said barrier but at least a portion of said trigger extends into said central flow bore;
(iii) a sensor wholly disposed within said second chamber, adapted to sense when said magnetic field changes across said barrier;
b. rotationally displacing said trigger when said launched object passes said trigger, thereby causing a change in magnetic field across said barrier;
c. sensing said change in magnetic field using said sensor; and
d. emitting a signal using a signal device.
2. The method of claim 1 , wherein only said magnetic field passes through said barrier.
3. The method of claim 1 , wherein said pressure sealing barrier can withstand a pressure differential across said barrier equal to at least the working pressure rating of said tool.
4. The method of claim 1 , wherein said mechanical trigger comprises a spring wire tongue that when displaced by passage of said launched object causes displacement of a magnet in proximity of said pressure sealing barrier.
5. The method of claim 1 , wherein said electronic sensor comprises a Hall-effect sensor that produces either an on or off signal.
6. The method of claim 1 , wherein said electronic sensor comprises a wire coil positioned in said second chamber so that movement of a magnet in said first chamber produces an electrical voltage in said wire coil.
7. The method of claim 1 , wherein said mechanical trigger comprises a spring wire tongue that when displaced by passage of said launched object causes displacement of a ferrous metal member in proximity to said pressure sealing barrier.
8. The method of claim 1 , wherein said electronic sensor comprises a Hall-effect sensor having a biasing magnet incorporated in said Hall-effect sensor.
9. The method of claim 1 , wherein said signal comprises an audible sound.
10. The method of claim 1 , wherein said signal device comprises at least one light emitting diode adapted to provide a visual signal when said launched object passes said indicating device.
11. The method of claim 1 , wherein said trigger comprises a wire configured such that passage of any objects at least 3 inches in diameter will displace said trigger, while loss circulation material will not displace said trigger.