MAGNETIC DISTURBANCE 1377 
Directly over the casing the dip is go’, indicating that the resultant 
vector is vertically downward and as the distance increases the dR vector 
rotates in a clockwise direction, becomes horizontal when d¢ is 180°, 
and has moved 46° into the second quadrant of the rectangular codrdinate 
system at a radial distance of 260 feet. The magnetic declination, which 
may be defined as the angle between the astromonic meridian and the 
magnetic meridian, will clearly depend on the azimuth selected for the 
profile, although the shape of the other curves will be the same regardless 
of the azimuth chosen. 
The composition of these anomalous components with the normal 
terrestrial components determines the absolute values of the magnetic 
elements in the region surrounding the casing head. Let us next con- 
sider these resultant effects, which are graphically illustrated for a 
magnetic north-south traverse in Figure 3. The Z component at any 
point, as would be anticipated, represents the algebraic sum of the anom- 
alous vertical intensity and the normal vertical intensity which would 
exist but for the presence of the magnetized casing. The normal vertical 
field strength, determined before the casing was set, was found to be 
49,552 gammas and the maximum departure from this normal value 
occurs directly over the casing, where it becomes 81,954 gammas. The 
normal value of the resultant R was 55,489 gammas and its peak inten- 
sity of 87,891 gammas is coincident with the Z curve. The north and 
south parts of the R, H, and ¢ profiles are not symmetrical with respect 
to the casing axis, because these curves are determined by the vector 
composition of the anomalous and normal components. The maximum 
departures of the horizontal element, from the normal value of 24,974 
gammas, occur in the immediate vicinity of the casing head, where the 
H curve indicates a variation of 25,000 gammas from a point 13 feet 
south to a position 15 feet north of the pipe. As for each azimuth the 
dH component is directed toward the casing, it is understood that the 
numerically lower values of H, for the north part of this profile, represent 
a subtractive effect, but south, the components are additive. Points 
of maximum and minimum for the angle of dip, which has a normal value 
of 63° 15’, occur adjacent to the casing, the relatively larger angles of 
inclination for the north part of the ¢ profile being traceable to the de- 
crease in horizontal intensity. The different curves indicate that the 
magnetic elements have returned to substantially normal values at 260 
feet in either direction from the casing. The declination profile is not 
shown because this element is subject to no variation, other than the 
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