March 19–25

I have been working on the final example for a casing paper — hopefully I will be sending the draft through next week! This example compares numerical results from SimPEG with a scale model simulation published in Augustin et al., 1989 (https://doi.org/10.1190/1.1442581).

Setup:

• 9m long pipes, one conductive: copper, one conductive and permeable: iron
• 0.6m co-axial source loop
• “Infinite” source loop midway along pipe
• “Semi-infinite”: source loop at top of pipe
• B-field receiver in pipe either at: L=0: in the same plane as the source, or L=1.49m: 1.49m below the source

When comparing the two, we see that there is good agreement in behaviour for L=1.49, good agreement for copper pipe and infinite iron pipe at L=0m, but a big disagreement for the semi-infinite iron pipe at L=0… why??

To figure out why, we have plotted the secondary magnetic flux density in the top few centimetres of the pipe. For reference, the primary is going upwards. Near the end of the pipe at z=0, we can see that there are significant edge effects. Even a few centimetre error changes from magnetic enhancement (secondary magnetic field going up — same orientation as the source) to magnetic shielding (secondary magnetic field going down — opposite orientation to the source). If we move the receiver 3cm down, we can recover a plot much closer to that observed by Augustin, 1989.

New Release: SimPEG 0.7.4

SimPEG 0.7.4 was merged this week; we added a parametric map for a block as was shown in the AEM2018 Abstract on Open source software for simulations and inversions of airborne electromagnetic data. Check out the release notes here: https://github.com/simpeg/simpeg/releases/tag/0.7.4.

At the meeting last week

Johnathan Kuttai presented on “Time-Series Processing — From Raw Signal to IP Decay”