STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

MWD and LWD 911
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
-G
TF = arc tan 2
G,
(4-1 76)
The gravity tool face angle is used to steer the well to the right, TF > 0, or to
the left, TF < 0.
Typical specifications for a gravity sensor are as follows:
Temperature
Operating = 0 to 200°C
Storage = -40 to 200°C
Scale factor = 0.01 V/OC
Power requirement
24 V nominal
Less than 100 mA
Output impedance
10 sz
Figure 4-226. Solid geometry representing the gravity tool face angle concept.