Gravity tool face angle

The gravity tool face angle, or angle between the plane defined by the borehole axis and the vertical and the plane defined by the borehole axis and the BHA axis below the bent sub, can also be calculated. Figure 4-226 shows the gravity tool face angle. It is readily calculated using the equation... 

The gravity tool face angle is used to steer the well to the right, TF > 0, or to the left, TF < 0. 

With the modern accelerometers and solid-state magnetometers, a complete set of data is available for inclination, tool face and azimuth calculation. Magnetic corrections can be done. Inclination can be calculated with Equations 4-174 and 4-175. The gravity tool face angle can be calculated with Equation 4-176. 

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