Induced polarization effect in time-domain electromagnetic prospecting, noise or signal?

SEG Lectures ◽  
2019 ◽  
Author(s):  
Hesham El-Kaliouby
Keyword(s):  
Time Domain ◽  
Polarization Effect ◽  
Induced Polarization ◽  
Time Domain Electromagnetic ◽  
Induced Polarization Effect

Decoupling induced polarization effect from time domain electromagnetic data in a Bayesian framework

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. A59-A63 ◽  
Author(s):  
Hai Li ◽  
Guoqiang Xue ◽  
Yiming He
Keyword(s):  
Time Domain ◽  
Computational Cost ◽  
Bayesian Framework ◽  
Induced Polarization ◽  
Linear Perturbation ◽  
Model Parameters ◽  
Bayesian Sampling ◽  
3D Space ◽  
Time Domain Electromagnetic ◽  
Induced Polarization Effect

We have developed a scheme for decoupling the induced polarization (IP) effect from time-domain electromagnetic (TDEM) data. This scheme is achieved by simultaneously sampling the resistivity and pseudochargeability in a Bayesian framework. The TDEM and IP responses are simulated separately with the sampled model parameters and then are stacked to fit the IP-affected TDEM data. Thus, the influence of the IP phenomenon is eliminated in the process of recovering the resistivity. To reduce the computational cost brought by the Bayesian sampling, we use a 2D parametrization instead of sampling the full 3D space and we use a linear perturbation approximation for calculating the IP response. The linearized inversion results are used as the initial model, and a multiple proposed points algorithm is used to accelerate the sampling. We validate the proposed method with synthetic and field examples showing that it restores accurate estimates of electrical structures from the TDEM data that are significantly affected by the IP phenomenon. Our method could advance the application of the TDEM method to the scenario in which the IP may affect the TDEM data and mask the underlying geologic targets.

scholarly journals Double Trapezoidal Wave Transmitting System with Controllable Turn-Off Edge

2020 ◽  
Vol 10 (21) ◽  
pp. 7932
Author(s):  
Yuan Jiang ◽  
Yanju Ji ◽  
Yibing Yu ◽  
Shipeng Wang ◽  
Yuan Wang
Keyword(s):  
Polarization Effect ◽  
Induced Polarization ◽  
Emission Current ◽  
Wire Loop ◽  
Transient Electromagnetic ◽  
Charging Time ◽  
The Earth ◽  
Electromagnetic Measurement ◽  
Induced Polarization Effect ◽  
Off Time

For time domain transient electromagnetic measurement, the negative sign often appears in the polarization region, which contains the induced polarization information. It is considered that the polarization effect is caused by the capacitance charge of the earth. Extending the turn-off time of the emission current means increasing the charging time, and reducing the charging voltage, which makes the polarization effect easier to observe. Therefore, a double trapezoidal wave transmitting system with a controllable turn-off edge is designed in this paper. In the process of current transmitting, the turn-off time can be controlled by changing the clamping voltage depending on the passive clamping technology. By cutting into the absorption resistance, the current oscillation can be eliminated under the condition of ensuring linearity. To verify the effectiveness of the system, we designed a polarized wire loop based on the filament model simulating the polarized earth. Comparing the response of the wire loop, the emission current with short and long turn-off times contributes to inducing the induction and polarization fields respectively. The double trapezoidal wave transmitting system with a controllable turn-off edge is suitable for measuring the induced polarization effect.

Electrical-prospecting method for hydrocarbon search using the induced-polarization effect

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. G179-G189 ◽  
Author(s):  
Sofia Davydycheva ◽  
Nikolai Rykhlinski ◽  
Peter Legeido
Keyword(s):  
Polarization Effect ◽  
Induced Polarization ◽  
Controlled Source ◽  
3D Environment ◽  
Electrical Prospecting ◽  
Displacement Currents ◽  
Source Excitation ◽  
Induced Polarization Effect ◽  
Hydrocarbon Deposits ◽  
Regions Of Russia

We propose a method of surface and marine electrical prospecting using controlled-source excitation. The method is designed to detect hydrocarbon deposits at depths of a few kilometers and to map their boundaries. The technique is based on imaging the induced-polarization (IP) parameters of the geologic formation. We use the fact that, because of the imaginary part of the electric conductivity, polarized media support wave propagation processes whose nature is similar to displacement currents induced by the dielectric permittivity. However, unlike displacement currents, these processes reveal themselves at much lower frequencies and, therefore, at greater depths. It is established that the ratio of the second and the first differences of the electric potential does not decay after the current turn-off in polarized media, whereas it decays quickly if the IP effect is absent. Thus, the IP response can be observed directly and separated from the electromagnetic (EM) response. We use a vertical focusing of the electric current to decrease the effect of laterally adjacent formations to apply a 1D layered model in a 3D environment. This method obtained promising results in several regions of Russia.

Inductive induced polarization effect in heliborne time-domain electromagnetic data for uranium exploration, northern part of Cuddapah Basin, India

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. B109-B120 ◽  
Author(s):  
Veldi Ramesh Babu ◽  
Indrajit Patra ◽  
Shailesh Tripathi ◽  
Sridhar Muthyala ◽  
Anand K. Chaturvedi
Keyword(s):  
Time Domain ◽  
Induced Polarization ◽  
Uranium Mineralization ◽  
Cuddapah Basin ◽  
Text Data ◽  
Argillic Alteration ◽  
Uranium Exploration ◽  
Time Domain Electromagnetic ◽  
Text Response ◽  
Lithologic Unit

The Peddagattu, Lambapur, Chitrial and Koppunuru uranium deposits along the northern margins of the Cuddapah Basin are confined to the middle Proterozoic unconformity interface between Archean basement granites and the overlying resistive quartzites. Negative transients observed in the coincident loop heliborne time-domain electromagnetic (HTEM) data over these deposits (occurring in outliers) are believed to be due to thick polarizable conductive zones occurring along the unconformity. Similar negative HTEM responses are recorded over the Gorukunta Tanda outlier. A ground spectral induced polarization (SIP) survey conducted over the outlier and ground geologic observations indicated an altered basement/regolith with thickness up to 5 m below 20–30 m thick quartzite. Interpretation of Cole-Cole parameters computed from the SIP data indicated a change in the dispersion. These Cole-Cole parameters were used in modeling negative HTEM data assuming a polarizable plate placed in a layered earth at a depth of approximately 50 m using the CSIRO LeroiAir program. A negative [Formula: see text] response in the late channels indicated that the negatives can be explained in terms of inductive induced polarization effects. Modeling of HTEM [Formula: see text] data for the profile through the Lambapur uranium deposit and the Gorukunta Tanda reveals the presence of a polarizable lithologic unit at a depth of approximately 40 m. This unit is interpreted as an argillic alteration of basement, with the presence of clay and/or disseminated sulfides as evidenced from the core extracted from the boreholes at depths below the highly resistive quartzite. Uranium mineralization is closely associated with altered basement and sulfides along the unconformity where the distinct negative electromagnetic (EM) signature is recorded. Furthermore, there exists a good correlation between the uranium mineralization grade and the thickness versus the averaged late-channel negative HTEM response over the known deposits. The negative EM response helped in locating the new target areas for uranium exploration.

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