Directional Concepts

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