MANUAL – REFLEX EZ-TRAC™ | 11
3.2 Direction of downhole object
When conducting directional drilling, a metal wedge is applied in the
borehole to force the drill bit to move out of the direction of the
existing hole. The direction of the downhole wedge has to be
determined in order to verify that the drilling will continue in the
desired direction.
Directional information is also needed in core orientation, impressions
of bore walls and for orientation of tools, such as downhole motors.
By combining a directional survey of the wedge with surveys of the
tool orientation, the position of the tool can be adjusted correctly.
3.2.1 Measurement of direction
The direction of a downhole object can be determined by measuring
the rotation of the survey instrument relative to gravity or magnetic
north.
3.3 Single shot survey
A single shot survey is carried out to determine the azimuth
(direction) and dip (inclination) at a certain point inside a borehole.
Single shot surveys are used at regular intervals as a hole is being
drilled. Based on the survey information, decisions regarding further
drilling can be made and corrections applied if needed. For example,
wedge setting might be needed to change the direction of the
borehole.
3.4 Multi shot survey
A multi shot survey is used to determine the regional and local
coordinates along a borehole path, in addition to the azimuth
(direction) and dip (inclination).
The multi shot survey data is used to calculate the position of a
borehole along its entire path. It is also an efficient method to identify
sharp changes in the borehole direction.
3.5 Orientation survey
An orientation survey is carried out to determine the orientation or
direction of a wedge during directional drilling, or to measure the
rotational position of a tool within the drill string or at the end of the
drill string.
Reference angle The orientation survey consists of two measurements; registration of
a reference at the surface and registration of the instrument rotation
at the survey station inside the hole.
Angle of rotation The control unit software displays the rotation (tool face) of the object,
compares it to the desired value, and gives the required angle of
rotation if the object is not in the correct position.
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