The present invention relates to the field of energy services. In particular, the invention relates to a method and system for detecting conditions inside a wellbore.
Conditions inside a wellbore can include sticking between a rotating pipe and material downhole. For example, during drilling the drill pipe can become stuck. If a drill pipe that is stuck downhole continues to be rotated at the surface, excessive torque forces can result in the pipe twisting off. Conditions detected in a wellbore can be used to control operations at the surface in a manner that reduces the risk of damaging equipment.
One embodiment of the invention of a system 100 for detecting conditions inside a wellbore is illustrated in
One example rotation detector is a light detector positioned to receive light from a light source at one point of each rotation. The light source can be placed on a structure that rotates at the same rate as the pipe proximate the surface. Another possibility is that the light detector itself rotates with the pipe while the light source is fixed. One potential light source would be a reflector. Another example rotation detector is a magnetic proximity switch that is positioned to encounter a target once per rotation of the pipe at the surface. Another example rotation detector is connected to the gearing of the top drive or Kelley and generates a signal corresponding to pipe rotation at the surface based on that gearing. Another example rotation detector is a magnetometer oriented in the X-Y plane with the pipe axis as the Z axis and rotationally fixed to the pipe or another structure that rotates at the same rate as the pipe. The magnetometer can detect rotation of the pipe by the corresponding changes in the strength of the earth's magnetic field as the magnetometer changes orientation as discussed in more detail with respect to
One embodiment of the system detects the rotation of the pipe at the surface. When the pipe gets stuck at a location below the surface, rotation at the surface can continue even though rotation below the surface has slowed or stopped. The pipe structure resists twisting of one portion of pipe relative to another, which is sometimes called “winding up.” The torque applied to the pipe at the surface is increased to maintain the rotation speed at the surface. Detection of more rotation of the pipe at the surface relative to rotation at a depth below the surface provides an indication that torque build up is occurring as the pipe winds up. Detecting torque build up and reacting to it can decrease the risk of equipment damage.
Winding up can occur repetitively in the form of torsional vibration. For example, a pipe can become stuck at a particular depth and begin to wind up. The downhole torque resulting from the wind up can become great enough to overcome the frictional force at the point of sticking so that the pipe will then unwind with sticking occurring again once the torque has reduced. Detecting the variations between rotation speeds at two or more points on the pipe can diagnose that torsional vibration is occurring, where it is occurring, and its magnitude.
The pipe 150 can include a number of pipe segments 150A–150D. In one embodiment of the invention, several rotation detectors 160A–160D are mounted in the pipe segments 150A–150D at different depths. One of the rotation detectors 160D can be positioned with the drill bit 170. Each rotation detector can be, for example, a magnetometer oriented in the X-Y plane with the pipe axis as the Z axis. As discussed above with respect to the surface detector included with the top drive 120, in different embodiments alternative rotation detectors can be substituted for the magnetometers. Such a magnetometer could be coupled to the pipe so that it rotates with the pipe. Each rotation of the pipe sweeps the magnetometer through a 360 degree change in orientation that would include the magnetic north and magnetic south orientations. The magnetic field strength measured by the magnetometer would vary depending upon the angle of the detector relative to the magnetic poles. The variation in detected magnetic field strength would correlate to the rotation of the pipe. The wellbore 140 is shown in a vertical orientation. A wellbore can also deviate from vertical. A magnetometer being used as a rotation detector, e.g., 160A, will detect smaller magnetic field strength deviations resulting from the magnetic poles when the wellbore deviates from vertical. The variation in magnetic field strength can also be detected in circumstances where another magnetic component is present. For example, a background magnetic component contributed by magnetization of the pipe or other instruments present in the pipe can be subtracted from the magnetometer measurement to produce a signal that varies in accordance with pipe rotation. In one embodiment, magnetometers mounted in the pipe at different depths can be used without the use of a pipe rotation detector proximate to the surface.
A circuit 130, such as a programmed microprocessor or dedicated logic, can be used to receive the measurements made by the rotation detector proximate to the surface 120 and one or more rotation detectors 160A–160D placed at various depths in the wellbore 140. In one embodiment, the circuit 130 can compare the measurements themselves. For example, if magnetometers are used both proximate to the surface as well as at a depth in the borehole, the magnetic strength readings can be directly compared. If the pipe is rotating at the same rate at the detector locations (for example, at the surface and downhole)(as another example, at two different depths downhole) the measured magnetic strength readings will stay in phase. The circuit 130 may employ some processing to account for timing. For example, there may be a delay in receiving information from one of the detectors that can be accounted for by the circuit so that measurements made at the same time are compared. Circuit 130 can also compare the detector measurements by calculating the rotation speed of the pipe at the detector locations and comparing the calculated speeds. When the comparison indicates a difference in rotation and different points of the pipe, the circuit 130 can generate a signal if the comparison meets a particular condition. For example, if the rotation speed downhole lowers relative to the rotation speed at the surface, over time the pipe will wind up and the circuit 130 can send a signal to the top drive or a rotary table to stop applying torque. Such a signal could prevent equipment damage, including damage to the pipe 150.
The circuit 130 can also compare measurements from several detectors 160A–160D positioned at different depths to estimate the depth at which the pipe 150 is stuck. For example, the circuit 130 can receive measurements from detector 120 proximate to the surface and two detectors 160A, 160C at different depths in the wellbore 140. If the difference in rotation speed is between the surface and both downhole depths, the circuit can estimate that the pipe 150 is stuck somewhere above the first detector 160A. If, however, there is a significant difference in rotation speed between the two downhole detectors 160A, 160C, the circuit 130 can estimate that the pipe 150 is stuck between the two detectors.
If the pipe is oriented vertically, its rotation will change the orientation of detectors in the X-Y plane, with the Z-axis being the pipe axis, to point at each of the cardinal directions in sequence. In the detectors are magnetometers, the change in cardinal orientation will vary the detection of the earth's magnetic field. The detected field will be an absolute maximum when the detector is oriented north or south and zero when the detector is oriented east or west.
In one embodiment, a difference is significant if it exceeds a predetermined threshold. As one example, the threshold may be a certain number of rotations difference per depth. Thus, if the threshold is one rotation for a measurement at a particular depth, in one embodiment, the threshold is two rotations at twice the depth, where the difference is in comparison to the surface. After a signal is generated at step 470, the likely sticking point is determined at 480 if there are multiple secondary parameters. For example, if a first parameter is measured proximate to the surface and two parameters are measured at different depths, the difference in parameters between the three measurements can determine a likely sticking point between the measurements with the greatest difference. The sticking point may also be identified by a nonlinear parameter value. For example, rotation speed may decrease linearly as a function of distance toward the surface from the stuck point, but the change of rotation between the sensors above and below the stuck point may not that follow that linear relationship.
Multiple measurements of rotation-correlated parameters also can be useful in downhole operations such as sliding. A sliding operation involves rotating a drill bit with a mud motor rather than by rotation of the drill string. The drill string may rotate at a different rate than the drill bit. One embodiment of the invention can monitor the rotation of the drill string at the surface and/or one or more depths and the rotation of the drill bit. In one embodiment, the rotation of the drill bit is monitored by detecting the rotation of the mud motor.
The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.
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Number | Date | Country | |
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20050193811 A1 | Sep 2005 | US |