Induced‐polarization effects in time‐domain electromagnetic measurements

Geophysics ◽  
1989 ◽  
Vol 54 (4) ◽  
pp. 514-523 ◽  
Author(s):  
Marcus F. Flis ◽  
Gregory A. Newman ◽  
Gerald W. Hohmann
Keyword(s):  
Relative Strength ◽  
Polarization Current ◽  
Sign Reversal ◽  
Positive Part ◽  
Polarization Effects ◽  
The Earth ◽  
Electromagnetic Measurements ◽  
Charging Current ◽  
Time Domain Electromagnetic ◽  
Cole Model

Sign reversals in the coincident‐loop transient response can be produced by employing a Cole‐Cole model in numerical TEM modeling of polarizable conductors. These reversals may be thought of in terms of a polarization current which changes sign during the transient, passing from a charging current at early times to a discharging current at late times. In a layered earth, the relative strength of this current compared to the normally induced vortex current dictates whether or not a reversal is seen. If the earth is conductive, the effects of the polarization current may never be seen. If, however, the earth is only moderately conductive, the polarization current may dominate. In the case of a 3-D polarizable conductor in a conductive host, the addition of a host response serves to delay the time of any sign reversal in the transient. Reducing the host rock response by increasing its resistivity enables the polarization current to dominate earlier. By bringing the conductor closer to the surface, the amplitude of the negative response can be made greater and hence the sign reversal brought earlier in time. In such cases, moderate polarization parameters may cause substantial negative responses. It is possible to interpret TEM anomalies exhibiting sign reversals. The location and geometry of a discrete polarizable conductor can be correctly assessed, and a valid but approximate TEM time constant can be measured, from the positive part of the transient before the sign reversal.

On: “Induced‐polarization effects in time‐domain electromagnetic measurements” by M. F. Flis, G. A. Newman, and G. W. Hohmann (GEOPHYSICS, 54, 514–523, April 1989).

Geophysics ◽  
1989 ◽  
Vol 54 (12) ◽  
pp. 1655-1656 ◽  
Author(s):  
Richard Smith
Keyword(s):  
Time Domain ◽  
Three Dimensional ◽  
Polarization Current ◽  
Electromagnetic Measurements ◽  
Charging Current ◽  
Time Domain Electromagnetic ◽  
Time Domain Response ◽  
The Time Domain ◽  
Theoretical Results ◽  
Insight Into

Flis et al. provide useful insight into the time‐domain response of three‐dimensional polarizable bodies; however, their inference that negative transients are caused by a polarization current which reverses direction disagrees with the previously published theoretical results of Smith et al. (1988) and Smith and West (1988), who found that the polarization current is always negative (provided that the chargeability m and charging current are positive).

A discussion of 2D induced polarization effects in airborne electromagnetic and inversion with a robust 1D laterally constrained inversion scheme

Geophysics ◽  
2019 ◽  
Vol 84 (2) ◽  
pp. E75-E88 ◽  
Author(s):  
Changhong Lin ◽  
Gianluca Fiandaca ◽  
Esben Auken ◽  
Marco Antonio Couto ◽  
Anders Vest Christiansen
Keyword(s):  
Synthetic Data ◽  
Induced Polarization ◽  
Negative Data ◽  
Polarization Effects ◽  
Bay Area ◽  
Time Domain Electromagnetic ◽  
Airborne Electromagnetic ◽  
Cole Model ◽  
And Inversion ◽  
Synthetic Models

Recently, the interest in the induced polarization (IP) phenomenon in airborne time-domain electromagnetic (ATEM) data has increased considerably. IP may affect the ATEM data significantly and mask underlying geologic structures. To simulate 2D airborne IP data, a 2D finite-element forward-modeling algorithm has been developed with the dispersive conductivity described by the well-known Cole-Cole model. We verify our algorithm by comparison with the 1D solution of the AarhusInv code. Two-dimensional forward responses on six synthetic models, mimicking archetypal 2D conductive and chargeable anomalies, have been generated, and the results indicate that 2D IP affects the data significantly. Differences between the 2D IP responses and the 1D IP responses are evident above the 2D anomalies and at their edges. These differences are similar to what is found when comparing 2D and 1D forward responses over conductive 2D anomalies without considering IP. We evaluate an effective robust inversion scheme to recover the 2D IP parameters using the 1D laterally constrained inversion (LCI) scheme. The inversion of the synthetic data using the robust scheme indicates that not only can the IP parameters be recovered, but also the IP inversions can provide more accurate resistivity sections than a resistivity-only inversion, in terms of resistivity values and anomaly thickness/depth. The field example from Hope Bay area in Canada is even more valuable, considering that part of the profile consists of only negative data, which cannot be inverted with a resistivity-only scheme. Furthermore, the edge effects at the anomaly boundaries are less pronounced in the IP parameters than in the resistivity parameter on the synthetic models with more conductive backgrounds.

scholarly journals On the pipeline polarization in the case of insulation delamination from its surface

2020 ◽  
Vol 2020 (1) ◽  
pp. 40-45
Author(s):  
V. V. Lukovych ◽  
Keyword(s):  
Current Density ◽  
Cathodic Protection ◽  
Polarization Potential ◽  
Polarization Current ◽  
Protection Zone ◽  
Average Value ◽  
The Earth ◽  
First Case ◽  
The Difference ◽  
Protection Potential

The cathodic protection parameters for two pipelines with a diameter of 1420 mm were calculated. The protection zone for the first pipeline is 6 km long and for the second one it is 5 km. The cathode station current is 12,9 A for the first pipeline and 4 A for the second one. There are a damage and detachment of pipeline insulation, andconsequently a thin layer of electrolyte is located in the detachment area between the metal surface and the insulation. Almost the entire surface of the pipeline has polarization potential. For the first pipeline, the values of the protection potential at neighboring measurement points change quite dramatically, the difference between them can reach tenths of a volt. The polarization current density at the ends of the protection zone is quite small, and accordingly the polarization potential is close to the corrosion potential. But in the vicinity of the drainage point, these values are much larger. The situation is almost the opposite for the second pipeline, where the cathode station current is 4 A. The current density is almost equally distributed throughout the protection zone, slightly larger at its ends. The polarization potential changes accordingly. Its values are larger than the first case. In the cathodic protection, the potential of the pipeline relative to ground zero is important. Its average value depends on the magnitude of the cathode station current. Its graph intersects the lower part of the protection potential graph in the first case and the middle of the graph in the second. The protection potential is the difference between the potential of the pipeline and the earth surface. In the first case, in the vicinity of the drainage point this difference is much larger inside compared to the ends of the zone. As a conclusion, in the practice of cathodic protection it is important to regulate the value of the cathode station current in order to achieve the optimum protection. Keywords: delamination, protection potential, polarization current density.

USE OF DECAY PATTERNS FOR THE CLASSIFICATION OF ANOMALIES IN TIME‐DOMAIN AEM MEASUREMENTS

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 1031-1041 ◽  
Author(s):  
G. J. Palacky
Keyword(s):  
Time Domain ◽  
Field Measurements ◽  
System Response ◽  
Electromagnetic Measurements ◽  
Time Domain Electromagnetic ◽  
Decay Pattern ◽  
Body Parameters ◽  
Flight Computer

Interpretation of time‐domain electromagnetic measurements normally comprises visual anomaly selection and determination of body parameters, such as conductance, depth, and dip. A study is made to examine the possibility of in‐flight computer interpretation on the basis of decay patterns. Analysis of system response over conducting loops, vertical and dipping sheets, horizontal strips, and a half‐space indicates that identification of models and some of their parameters by decay patterns is feasible. By the simultaneous use of vertical and horizontal coil receivers, a reliable recognition of models may be achieved. While the secondary magnetic field over a conducting loop decays exponentially, other models show distinctive nonexponential patterns. Decay patterns are affected by conductance and conductor size, but less by depth and dip variations. Field measurements indicate that decay pattern may be used to distinguish between geologic bodies of various types.

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