Depth of Investigation for Small Broadband Electromagnetic Sensors

2004 ◽  
Author(s):  
Haoping Huang
Keyword(s):  
Electromagnetic Sensors ◽  
Depth Of Investigation

Depth of investigation for small broadband electromagnetic sensors

Geophysics ◽  
2005 ◽  
Vol 70 (6) ◽  
pp. G135-G142 ◽  
Author(s):  
Haoping Huang
Keyword(s):  
Detection Threshold ◽  
Data Interpretation ◽  
Skin Depth ◽  
High Threshold ◽  
Electromagnetic Sensors ◽  
Quantitative Understanding ◽  
Processing Techniques ◽  
Simple Equations ◽  
Depth Of Investigation ◽  
Conductivity Contrast

The depth of investigation in electromagnetic (EM) soundings is a maximum depth at which a given target in a given host can be detected by a given sensor. It is of primary interest in EM exploration, particularly for small EM sensors having negligible separation between the transmitter and receiver coils. The depth of investigation is related to many factors, such as sensor sensitivity, precision, operating frequencies, ambient noise level, target and host properties, and the techniques used in data processing and interpretation. Quantitative understanding of the relationships between the depth of investigation and these factors will help users meet their geologic objectives, avoid unnecessary survey expenses, and display meaningful geologic features. Simple equations to estimate the depth of investigation for handheld EM sensors have been derived from analyzing the EM response based on layered half-space models. The results show that the depth of investigation is approximately proportional to the square root of the skin depth in the host for a given detection threshold and conductivity contrast between the target and host. For a given skin depth, the depth of investigation increases with the target conductivity and conductivity contrast and decreases with the detection threshold. Choosing a threshold mainly depends on the S/N ratio of the EM data if the sensor setup, data acquisition methods, and processing techniques are well established. A high threshold such as 20% or 30% is recommended for resistive targets or in areas where environmental noise is high or where terrain conductivity is low (<50 mS/m). In contrast, a threshold as low as 5% or 10% can be used for conductive targets in quiet areas. Field examples are presented to illustrate how to use the depth of investigation in data interpretation and presentation.

scholarly journals The Application of Electromagnetic Sensors for Determination of Cherenkov Cone Inside and in the Vicinity of the Detector Volume in Any Environment Known

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 992
Author(s):  
Valeriu Savu ◽  
Mădălin Ion Rusu ◽  
Dan Savastru
Keyword(s):  
Energy Levels ◽  
Cherenkov Detector ◽  
Electromagnetic Sensors ◽  
The Cost ◽  
Information Errors ◽  
The Universe ◽  
Large Frequency ◽  
Very High ◽  
Detector Volume

The neutrinos of cosmic radiation, due to interaction with any known medium in which the Cherenkov detector is used, produce energy radiation phenomena in the form of a Cherenkov cone, in very large frequency spectrum. These neutrinos carry with them the information about the phenomena that produced them and by detecting the electromagnetic energies generated by the Cherenkov cone, we can find information about the phenomena that formed in the universe, at a much greater distance, than possibility of actually detection with current technologies. At present, a very high number of sensors for detection electromagnetic energy is required. Thus, some sensors may detect very low energy levels, which can lead to the erroneous determination of the Cherenkov cone, thus leading to information errors. As a novelty, we propose, to use these sensors for determination of the dielectrically permittivity of any known medium in which the Cherenkov detector is used, by preliminary measurements, the subsequent simulation of the data and the reconstruction of the Cherenkov cone, leading to a significant reduction of problems and minimizing the number of sensors, implicitly the cost reductions. At the same time, we offer the possibility of reconstructing the Cherenkov cone outside the detector volume.

Revealing Hidden Information: High-Resolution Logging-While-Drilling Slowness Measurements and Imaging Using Advanced Dual Ultrasonic Technology

2021 ◽  
Vol 62 (1) ◽  
pp. 89-108
Author(s):  
Matthew Blyth ◽  
◽  
Naoki Sakiyama ◽  
Hiroshi Hori ◽  
Hiroaki Yamamoto ◽  
...  
Keyword(s):  
High Resolution ◽  
Elastic Wave ◽  
Horizontal Wells ◽  
Wellbore Stability ◽  
Frequency Range ◽  
Ultrasonic Technology ◽  
Logging While Drilling ◽  
Pulse Echo ◽  
Depth Of Investigation ◽  
Wave Properties

A new logging-while-drilling (LWD) acoustic tool has been developed with novel ultrasonic pitch-catch and pulse-echo technologies. The tool enables both high-resolution slowness and reflectivity images, which cannot be addressed with conventional acoustic logging. Measuring formation elastic-wave properties in complex, finely layered formations is routinely attempted with sonic tools that measure slowness over a receiver array with a length of 2 ft or more depending upon the tool design. These apertures lead to processing results with similar vertical resolutions, obscuring the true slowness of any layering occurring at a finer scale. If any of these layers present significantly different elastic-wave properties than the surrounding rock, then they can play a major role in both wellbore stability and hydraulic fracturing but can be absent from geomechanical models built on routine sonic measurements. Conventional sonic tools operate in the 0.1- to 20-kHz frequency range and can deliver slowness information with approximately 1 ft or more depth of investigation. This is sufficient to investigate the far-field slowness values but makes it very challenging to evaluate the near-wellbore region where tectonic stress redistribution causes pronounced azimuthal slowness variation. This stress-induced slowness variation is important because it is also a key driver of wellbore geomechanics. Moreover, in the presence of highly laminated formations, there can be a significant azimuthal variation of slowness due to layering that is often beyond the resolution of conventional sonic tools due to their operating frequency. Finally, in horizontal wells, multiple layer slownesses are being measured simultaneously because of the depth of investigation of conventional sonic tools. This can cause significant interpretational challenges. To address these challenges, an entirely new design approach was needed. The novel pitch-catch technology operates over a wide frequency range centered at 250 kHz and contains an array of receivers having a 2-in. receiver aperture. The use of dual ultrasonic technology allows the measurement of high-resolution slowness data azimuthally as well as reflectivity and caliper images. The new LWD tool was run in both vertical and horizontal wells and directly compared with both wireline sonic and imaging tools. The inch-scale slownesses obtained show characteristic features that clearly correlate to the formation lithology and structure indicated by the images. These features are completely absent from the conventional sonic data due to its comparatively lower vertical resolution. Slowness images from the tool reflect the formation elastic-wave properties at a fine scale and show dips and lithological variations that are complementary to the data from the pulse-echo images. The physics of the measurement are discussed, along with its ability to measure near-wellbore slowness, elastic-wave properties, and stress variations. Additionally, the effect of the stress-induced, near-wellbore features seen in the slowness images and the pulse-echo images is discussed with the wireline dipole shear anisotropy processing.

Reply to comments on “Performance assessment of factory and field calibrations for electromagnetic sensors in a loam soil”

2018 ◽  
Vol 203 ◽  
pp. 272-276 ◽  
Author(s):  
D.R. Rudnick ◽  
T. Lo ◽  
J. Singh ◽  
R. Werle ◽  
F. Muñoz-Arriola ◽  
...  
Keyword(s):  
Performance Assessment ◽  
Electromagnetic Sensors ◽  
Loam Soil
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