Page 256 - Well Logging and Formation Evaluation

246 Well Logging and Formation Evaluation

Using F tot = 25.6mT, x = 7.5ft yields P = 1681mWb.
The field due to such a monopole may be modelled and compared to
the measured readings. In order to do this, construct a spreadsheet as
follows:
For all the survey points model the field that would be seen in the high-
side reference system:
Determine the x, y and z components of unit vectors in the HS,
HSR, and RVEC directions. Calculate F.HSŸ, F.HSRŸ and F.RVECŸ, in
order to determine F hs , F hsr and F ax . Calculate AX dir and HS dir from these
quantities.
Overlay the modelled and measured data. Initially the match is not very
good. Because of the nature of the well trajectories (relief well passing
to the right of the target well going north to south with an inclination of
~50deg) the peaks can be aligned by moving the target well north or south.
The height of the peaks may be adjusted by moving the target well east
or west. By manually adjusting the assumed pole position on a trial-and-
error basis it was found that the best fit occurred when the target well was
moved 1.5ft west and 8.5ft north. After shifting the target well you should
end up with the following components:

Depth TVD F hs F hsr F ax F tot F xy AX dir HS dir

2685.00 2073.40 -0.01 -0.01 -0.16 0.16 0.01 175.14 227.71
2697.00 2080.70 -0.01 -0.02 -0.20 0.20 0.02 174.77 234.06
2707.00 2086.70 -0.02 -0.01 -0.26 0.26 0.02 175.29 220.24
2717.00 2092.70 -0.03 -0.03 -0.35 0.35 0.04 173.16 230.48
2727.00 2098.70 -0.02 -0.06 -0.48 0.49 0.06 172.93 254.70
2740.00 2105.70 -0.08 -0.11 -0.80 0.81 0.14 170.54 234.72
2750.00 2111.70 -0.16 -0.26 -1.35 1.39 0.30 167.40 238.53
2760.00 2117.60 -0.52 -0.75 -2.67 2.82 0.91 161.22 235.38
2770.00 2123.70 -2.13 -3.83 -6.52 7.85 4.38 146.16 240.89
2780.00 2129.70 -12.92 -20.63 -4.66 24.78 24.34 100.88 237.97
2790.00 2135.80 -3.93 -6.29 8.35 11.17 7.42 41.63 238.02
2800.00 2141.90 -0.76 -1.19 3.32 3.61 1.41 22.95 237.43
2810.00 2148.00 -0.22 -0.35 1.60 1.65 0.42 14.63 238.16
2820.00 2154.10 -0.02 -0.15 0.92 0.93 0.15 9.38 262.97
2830.00 2161.20 -0.05 -0.07 0.58 0.58 0.09 8.99 234.87
2840.00 2167.30 -0.03 -0.05 0.40 0.41 0.06 7.91 237.10
2850.00 2173.50 -0.02 -0.03 0.30 0.30 0.03 6.10 237.94
2860.00 2179.70 -0.01 -0.02 0.23 0.23 0.02 5.33 237.96