Dogleg
an abrupt change in direction in the wellbore, frequently resulting in the formation of a key-seat.
a sharp bend permanently put in an object such as a pipe, wire rope, or a wire rope sling.
Deflection angel > 3o/100 ft
Angle of Deflection
—in directional drilling, the angle at which a well diverts from vertical
—usually expressed in degrees
—In vertical, being zero.
Azimuth
—in directional drilling, the direction of the wellbore or of the face of a deflection tool in degrees (0 -359 ) clockwise from true north.
—an arc of the horizon measured between a fixed point (such as true north) and the vertical circle passing through the center of an object.
Steering Tool
—A directional survey instrument used in combination with a deflected downhole motor. It shows, on a rig floor monitor, the inclination and direction of a downhole sensing unit.
—MWD+LWD
Systems and Coordinates
Depth Reference
—Measured Depth (MD)
—True Vertical Depth (TVD)
Inclination (Drift)
—The angle (in degrees) between the local vertical (local gravity vector as indicated by a plumb bob) and the tangent to the well bore axis at a particular point.
—By oilfield convention, 0° is vertical and 90° is horizontal.
Toolface
—Rigsite use of the term “toolface” is often used as a shortening of the phrase “toolface orientation”. This can be expressed as a direction from North or topside of the wellbore.
—Toolface Orientation is the angular measurement of the toolface of a deflection tool with respect to either North or up (highside).
Highside/Magnetic Toolface
—Highside Toolface
—indicates whether a component is facing up, down, to the left or right
—Magnetic Toolface
—an angular measurement from North
Mag TFO = Azimuth + Highside
Azimuth (Hole Direction)
—the direction of the borehole on the horizontal plane, measured as a clockwise angle (0°- 360°) from the North reference.
—All magnetic tools give readings referenced to Magnetic North; however, the final calculated coordinates are referenced to True North
Quadrant Bearings
—the directions are expressed in degrees from 0°to 90° measured from North in the two Northern quadrants and from the South in the Southern quadrants, e.g., N87°E, S12°W, S90°W.
Direction Measurement
—Azimuth Reference
—Quadrant Bearings
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