Geology Reference
In-Depth Information
We can replace this “recipe” with one that estimates for both horizontal
and vertical resistivities without changes to hardware or logging procedures.
We illustrate this using our nondipolar simulator which, we again note, does not
bear the limiting physical restrictions borne by existing models. The simulator
allows rapid computations in batch mode. For discussion purposes, consider a
homogeneous, infinite but fully anisotropic medium and then determine phase
and amplitude trends versus resistivity variations. We focus on near and far
Receivers 1 and 2 at 15.187 and 22.781 in and consider 400 kHz and 2 MHz
frequencies. Each simulation requires about five seconds for a total time under
two minutes for conventional Intel i5 computers. Computed results appear in
Figure 8.9.1a,b,c,d, Figure 8.9.2a,b and Figure 8.9.3 which follow.
PHASE (DEG)
Frequency, 400,000 Hz; Transmitter-to-Receiver, 15.187 in.
R v = 0.1
m
v = 1
m v = 10
m
31.63
68.37
80.53
R h = 0.1
m
80.75
80.26
86.44
R h = 1
m
-29.77
89.28
88.99
R h = 10
m
AMPLITUDE (VOLTS)
Frequency, 400,000 Hz; Transmitter-to-Receiver, 15.187 in.
R v = 0.1
m
v = 1
m v = 10
m
0.001225
0.004339
0.008836
R h = 0.1
m
0.0005528
0.001929
0.005180
R h = 1
m
0.0001075
0.0005670
0.001972
R h = 10
m
Figure 8.9.1a. 400 kHz results, receiver at 15.187 in.
Note that our assumed resistivities vary by an order-of-magnitude per
increment. This is taken to keep computations to a minimum. As a result, phase
oscillations will appear to be large from one simulation to another; rapid
changes from box-to-box may suggest numerical instabilities, but in fact, all
results were obtained quickly and stably. In order to clearly emphasize our ideas
and data analysis approach, we will therefore focus on amplitude results (which
vary much more smoothly) in the following presentation.
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