STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Table 4-119
Accelerometer Output for 30" of Hole Deviation
Angle and Various Tool-Face Angles
MWD and LWD 917
Hole Axis x Axis y Axis z
Deviation (") Tool Face (") (mA) (mA) (mA)
30
30
30
30
30
30
30
30
30
-1 80
-1 35
-90
-45
0
45
90
135
180
-1.50
-1.06
0.00
1.06
1.50
1.06
0.00
-1.06
-1.50
0.00
-1.06
-1.50
-1.06
0.00
1.06
1.50
1.06
0.00
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
1. Compute the inclination of the borehole. Are the accelerometers working
properly? Why?
2. Compute the tool face angle, clockwise and counterclockwise. If we drill
ahead with this angle is the hole going to turn left or right?
3. Compute the field disturbance Hdc due to the drill collars.
4. Compute the inclination of the corrected magnetic field. Does it check with
the local data? What could prevent this inclination from being correct?
5. Give the principle of one of the borehole azimuth calculation methods.
Solution
1. The inclination is i = 4.27". Yes, the accelerometers work properly because
2. The tool-face angle is TF = 26.56'. The borehole is turning right.
3. Hz = 0.469 G, H,, = 0.014 G.
4. Corrected field inclination: 25.69". External disturbance: nearby casing or
drill collar hot spots.
5. If Z is the borehole axis unit vector,
compute A = G x Z (vector product)
B=GxH
and
AaB
cosa = -
1-41 PI
(scalar product)
Example 3: Steering Tool Measurements-Tool
Deviation, and Azimuth
Face,
A steering tool is normally used during drilling with a mud motor and is
connected to the surface with an electric wireline. The sensing devices shown
in Figure 4-232 are also used in most MWD mud pulse systems. The coordinates