1. Field of the Invention
This invention is related to apparatuses, systems, and methods for locating the point at which a pipe, e.g. a drill string, is stuck in an opening or a hole, e.g. in a hollow tubular or in a borehole.
2. Description of Related Art
It is useful in well bore operations to know the point at which one tubular is stuck within another or within a wellbore. Such knowledge makes it possible to accurately locate tools or other items above, adjacent, or below the point at which the tubular is stuck. The prior art includes a variety of apparatuses and methods for ascertaining the location of stuck pipe. In general these methods employ an instrument which is lowered into a tubular to sense deformations in the tubular when torsion or tension is applied to it. Readings taken at successive depths are recorded analyzed and interpreted to determine the depth at which the tubular is stuck.
There are four general types of sensing methods employed in the oil-field industry for detecting stress/strain or movement in pipe to determine a stuck pipe location. Three of these methods use only one sensor to detect both rotational and lineal displacement of pipe, while the fourth uses two sensors. One of the methods employs no down-hole electronics such as an oscillator.
One method employs an apparatus to which pipe is magnetically coupled and which detects pipe movement by sensing a change in magnetic flux. Forces applied to the pipe modify the characteristics of the coupled magnetic field which are noted at the surface with the aid of a downhole oscillator.
A second method, described in U.S. Pat. No. 3,006,186, employs an inductor that is mechanically attached to pipe at two points. The inductor is so arranged to have within it a gap in permeable material. The gap is modified in dimension in relation to any pipe movement and the modifications are registered at the surface. This method does not use a downhole oscillator to measure torque or stretch of pipe, but it responds nonlinearly to pipe movement and employs only one sensor.
A third method, described in U.S. Pat. No. 3,095,736, employs a single inductor that is mechanically attached to pipe at two points. This single sensor equipped design operates linearly and responds to mechanical movement by physically altering the permeability of the inductor which is then coupled to a downhole oscillator that changes frequency in relation to the pipe stress or strain measured.
A fourth method, described in U.S. Pat. No. 4,402,219, employs two sensors, independent of each other, which are mechanically attached to pipe at two points. This system uses an LVDT (linear voltage differential transformer) to detect linear displacement of pipe (stretch/compression); and uses a RVDT (rotary voltage differential transformer) to detect rotational movement. These types of sensors require sustained excitation from a stable oscillator, and in freepoint wireline applications, require the oscillator, and other electronics, to be located downhole.
There has long been a need for an efficient and an effective stuck pipe locator and a method for location stuck pipe. There has long been a need for such devices, and methods which overcome the problems associated with prior art devices. There has long been a need for such devices and methods which overcome the problems associated with the use of a single sensor and with the use of powered downhole electronics. There has long been a need for such devices and methods which overcome calibration and repair problems encountered with certain prior art devices. There has long been a need for such devices and methods which accurately determine the temperature at downhole locations in a borehole.