Magnetic and Gravity Toolface and How To Interpret The Meaning For Directional Drilling

Magnetic and gravity tooสface are terms in directional drilling world to describe the direction of the well. They are different in meaning and application therefore this article will teach you about these terminologies and how to read it.


Magnetic Toolface
The magnetic toolface is an angle projection onto the horizontal plane between the tool face and magnetic north. Typically, directional tools use the magnetic tool face when the inclination is less than 5 degree. The Figure 1 demonstrates that the mud motor is lined up to kick off at 30 degree azimuth magnetic.

Figure 1 - Magnetic Toolface
Figure 1 – Magnetic Toolface Continue reading

What are Magnetic Toolface and Gravity Toolface?

Magnetic Toolface: It is the direction, in the horizontal plane, the bent sub scribe line is pointing with regard to the north reference (Grid, Mag, or True). Magnetic orientation is used when the inclination of the wellbore is less than 5° to 8°. When the inclination is below this amount, the survey instrument cannot accurately determine the highside of the instrument for orientation purposes. The toolface will be presented in azimuth or quadrant form, referenced to magnetic north. The magnetic toolface reading is whatever magnetic direction the toolface is pointed. If the orientation lug on the survey instrument is pointed towards S 20 E, then the magnetic toolface would be 160°.

Gravity Toolface : It is the angular distance that a bent sub scribe line is turned, about the tool axis, relative to the high side of the hole. If the inclination of the wellbore is above 5° to 8°, then the gravity toolface can be used. The toolface will be referenced to the highside of the survey instrument, no matter what the hole direction of the survey instrument is at the time. The toolface will be presented in a number of degrees either right or left of the highside. For example, a toolface pointed to the highside of the survey instrument would have a gravity toolface of 0°. A toolface pointed to the lowside of the survey instrument would have a gravity toolface of 180°. If the orientation lug was rotated to the right of highside, the gravity toolface would be 70° to the right.

Reference books: Directional Drilling Books