Theory of induced‐polarization logging in a borehole

Geophysics ◽  
1986 ◽  
Vol 51 (9) ◽  
pp. 1830-1849 ◽  
Author(s):  
R. Freedman ◽  
J. P. Vogiatzis
Keyword(s):  
Low Frequency ◽  
Induced Polarization ◽  
Time Dependent ◽  
Frequency Effect ◽  
Frequency Interval ◽  
Nonlinear Relationship ◽  
Theoretical Understanding ◽  
Resistivity Logging ◽  
Downhole Measurements ◽  
Phase Angles

Currently, there is interest by the petroleum well‐logging industry in the potential use of induced polarization (IP) measurements to improve formation evaluation in shaly sands. Shell Development Company has constructed an experimental four‐electrode IP and resistivity logging tool to obtain downhole measurements in shaly sands. This study contributes to the theoretical understanding and interpretation of the dynamic (i.e., time‐dependent) response of this type of downhole IP logging device. A low‐frequency (e.g., 32 Hz or less) electric current oscillating at a single fixed frequency is applied between a pair of current electrodes in a borehole. The resulting voltages induced between pairs of potential measuring electrodes in the borehole are calculated by solving the time‐dependent Maxwell’s equations. Inductive electromagnetic (EM) coupling contributions to apparent (e.g., measured) IP phase angles are automatically taken into account. The model is applied to the study of normal logging arrays for which the voltage measuring electrodes are interior to the current electrodes. The model responses are calculated for normal arrays in both infinitely thick noninvaded formations and infinitely thick invaded formations. EM coupling contributions to apparent IP phase angles have an approximately universal dependence on a scaling parameter defined here. The scaling relationship permits the quantitative estimate of EM coupling effects for specific tool parameters (i.e., electrode spacings and frequencies) and formation characteristics (i.e., apparent conductivities). Therefore, scaling relationships of this type should be useful in the design of IP tools. An inverse method, developed for determining true formation IP phase angles and resistivities from apparent values measured by an IP tool, utilizes data from multiple pairs of voltage‐measuring electrodes and exploits the fact that, for the systems of interest, the inverse resistivity and IP problems can be “decoupled.” The assumption that IP phase angles have a logarithmic dependence on frequency over a decade frequency interval leads to a nonlinear relationship between percent frequency effect (PFE) and IP phase angle. This nonlinear relationship agrees well with experimental data.

scholarly journals Priming effects in the recognition of simple and complex words and pseudowords

2018 ◽  
Vol 39 (2) ◽  
pp. 198-222
Author(s):  
Miguel Lázaro ◽  
Víctor Illera ◽  
Javier Sainz
Keyword(s):  
Word Recognition ◽  
Low Frequency ◽  
Morphological Processing ◽  
Orthographic Processing ◽  
Frequency Effect ◽  
Experimental Conditions ◽  
Priming Effects ◽  
The Third ◽  
Complex Words ◽  
Intense Debate

AbstractWhether morphological processing of complex words occurs beyond orthographic processing is a matter of intense debate. In this study, morphological processing is examined by presenting complex words (brujería -> brujo –witchcraft -> witch), as well as simple (brujaña->brujo) and complex pseudowords (brujanza ->brujo), as primes in three masked lexical decision tasks. In the first experiment, the three experimental conditions facilitated word recognition in comparison to the control condition, but no differences emerged between them. Given the importance of the surface frequency effect observed, a second experiment was conducted. The results fully replicate those observed in the first one, but this time with low frequency targets. In the third experiment, vowels were removed from the stems of primes to reduce the orthographic overlap between primes and targets and, therefore, the influence of the embedded stem effect. The results show facilitative effects only for complex words. However, paired comparisons show no differences between experimental conditions. The overall results show the central role played by the processing of stems in visual word recognition and are explained in terms of current models of morphological processing.

IP interpretation in environmental investigations

Geophysics ◽  
2002 ◽  
Vol 67 (1) ◽  
pp. 77-88 ◽  
Author(s):  
Lee D. Slater ◽  
David Lesmes
Keyword(s):  
Field Experiments ◽  
Low Frequency ◽  
Environmental Parameters ◽  
Clay Content ◽  
Chemistry Laboratory ◽  
Frequency Effect ◽  
Resistivity Method ◽  
Surface Polarization ◽  
Capacitive Properties ◽  
Diffusion Polarization

The induced polarization (IP) response of rocks and soils is a function of lithology and fluid conductivity. IP measurements are sensitive to the low‐frequency capacitive properties of rocks and soils, which are controlled by diffusion polarization mechanisms operating at the grain‐fluid interface. IP interpretation typically is in terms of the conventional field IP parameters: chargeability, percentage frequency effect, and phase angle. These parameters are dependent upon both surface polarization mechanisms and bulk (volumetric) conduction mechanisms. Consequently, they afford a poor quantification of surface polarization processes of interest to the field geophysicist. A parameter that quantifies the magnitude of surface polarization is the normalized chargeability, defined as the chargeability divided by the resistivity magnitude. This parameter is proportional to the quadrature conductivity measured in the complex resistivity method. For nonmetallic minerals, the quadrature conductivity and normalized chargeability are closely related to lithology (through the specific surface area) and surface chemistry. Laboratory and field experiments were performed to determine the dependence of the standard IP parameters and the normalized chargeability on two important environmental parameters: salinity and clay content. The laboratory experiments illustrate that the chargeability is strongly correlated with the sample resistivity, which depends on salinity, porosity, saturation, and clay content. The normalized chargeability is shown to be independent of the sample resistivity and it is proportional to the quadrature conductivity, which is directly related to the surface polarization processes. Laboratory‐derived relationships between conductivity and salinity, and normalized chargeability and clay content, are extended to the interpretation of 1‐D and 2‐D field‐IP surveys. In the 2‐D survey, the apparent conductivity and normalized chargeability data are used to segment the images into relatively clay‐free and clay‐rich zones. A similar approach can eventually be used to predict relative variations in the subsurface clay content, salinity and, perhaps, contaminant concentrations.

Effect of Low-Frequency Modulation on Thermal Convection Instability

2001 ◽  
Vol 56 (6-7) ◽  
pp. 509-522 ◽  
Author(s):  
P. K. Bhatia ◽  
B. S. Bhadauria
Keyword(s):  
Asymptotic Solution ◽  
Temperature Difference ◽  
Frequency Modulation ◽  
Thermal Convection ◽  
Low Frequency ◽  
Horizontal Layer ◽  
Time Dependent ◽  
Stability Criteria ◽  
Steady Temperature ◽  
The Stability

Abstract The stability of a horizontal layer of fluid heated from below is examined when, in addition to a steady temperature difference between the horizontal walls of the layer a time-dependent low-frequency per­ turbation is applied to the wall temperatures. An asymptotic solution is obtained which describes the be­ haviour of infinitesimal disturbances to this configuration. Possible stability criteria are analyzed and the results are compared with the known experimental as well as numerical results.

Nonword repetition and levels of abstraction in phonological knowledge

2006 ◽  
Vol 27 (4) ◽  
pp. 577-581 ◽  
Author(s):  
Benjamin Munson
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Nonword Repetition ◽  
Chronological Age ◽  
Frequency Effect ◽  
Vocabulary Size ◽  
Levels Of Abstraction ◽  
Opposite Pattern ◽  
The Difference ◽  
Restriction Of Range

Susan Gathercole's Keynote Article (2006) is an impressive summary of the literature on nonword repetition and its relationship to word learning and vocabulary size. When considering research by Mary Beckman, Jan Edwards, and myself, Gathercole speculates that our finding of a stronger relationship between vocabulary measures and repetition accuracy for low-frequency sequences than for high-frequency sequences is due to differences in the range of the two measures. In our work on diphone repetition (e.g., Edwards, Beckman, & Munson, 2004; Munson, Edwards, & Beckman, 2005) we tried to increase the range in our dependent measures by coding errors on a finer grained scale than simple correct/incorrect scoring would allow. Moreover, restriction of range does not appear to be the driving factor in the relationship between vocabulary size and the difference between high- and low-frequency sequence repetition accuracy (what we call the frequency effect) in at least one of our studies (Munson et al., 2005). When the children with the 50 lowest mean accuracy scores for high-frequency sequences were examined, vocabulary size accounted for 10.5% of the variance in the frequency effect beyond what was accounted for by chronological age. When the 50 children with the highest mean accuracy scores for high-frequency sequences were examined (a group in which the range of high-frequency accuracy scores was more compressed, arguably reflecting ceiling effects), an estimate of vocabulary size accounted for only 6.9% of the frequency effect beyond chronological age. The associated β coefficient was significant only at the α<0.08 level. This is the opposite pattern than Gathercole's argument would predict.

Mapping of induced polarization using natural fields

Geophysics ◽  
2001 ◽  
Vol 66 (1) ◽  
pp. 137-147 ◽  
Author(s):  
Erika Gasperikova ◽  
H. Frank Morrison
Keyword(s):  
Electric Field ◽  
Surrounding Medium ◽  
Low Frequency ◽  
Induced Polarization ◽  
The Body ◽  
Electromagnetic Response ◽  
Frequency Dependent ◽  
Finite Body ◽  
Electric Field Profile ◽  
Measured Response

The observed electromagnetic response of a finite body is caused by induction and polarization currents in the body and by the distortion of the induction currents in the surrounding medium. At a sufficiently low frequency, there is negligible induction and the measured response is that of the body distorting the background currents just as it would distort a direct current (dc). Because this dc response is not inherently frequency dependent, any observed change in response of the body for frequencies low enough to be in this dc limit must result from frequency‐dependent conductivity. Profiles of low‐frequency natural electric (telluric) fields have spatial anomalies over finite bodies of fixed conductivity that are independent of frequency and have no associated phase anomaly. If the body is polarizable, the electric field profile over the body becomes frequency dependent and phase shifted with respect to a reference field. The technique was tested on data acquired in a standard continuous profiling magnetotelluric (MT) survey over a strong induced polarization (IP) anomaly previously mapped with a conventional pole‐dipole IP survey. The extracted IP response appears in both the apparent resistivity and the normalized electric field profiles.

scholarly journals Dynamic Pulse Buckling of Composite Stanchions in the Sub-Cargo Floor Area of a Civil Regional Aircraft

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3594
Author(s):  
Andrea Sellitto ◽  
Francesco Di Caprio ◽  
Michele Guida ◽  
Salvatore Saputo ◽  
Aniello Riccio
Keyword(s):  
Numerical Model ◽  
Numerical Models ◽  
Low Frequency ◽  
Time Dependent ◽  
Structural Behavior ◽  
Cyclic Loads ◽  
Civil Aircraft ◽  
Compressive Loads ◽  
Pulse Buckling ◽  
Implicit And Explicit

This work is focused on the investigation of the structural behavior of a composite floor beam, located in the cargo zone of a civil aircraft, subjected to cyclical low-frequency compressive loads with different amplitudes. In the first stage, the numerical models able to correctly simulate the investigated phenomenon have been defined. Different analyses have been performed, aimed to an exhaustive evaluation of the structural behavior of the test article. In particular, implicit and explicit analyses have been considered to preliminary assess the capabilities of the numerical model. Then, explicit non-linear analyses under time-dependent loads have been considered, to predict the behavior of the composite structure under cyclic loading conditions. According to the present investigation, low-frequency cyclic loads with peak values lower than the static buckling load value are not capable of triggering significant instability.

scholarly journals Slow-paced inspiration regularizes alpha phase dynamics in the human brain

2020 ◽  
Vol 123 (1) ◽  
pp. 289-299 ◽  
Author(s):  
Shen-Mou Hsu ◽  
Chih-Hsin Tseng ◽  
Chao-Hsien Hsieh ◽  
Chang-Wei Hsieh
Keyword(s):  
Low Frequency ◽  
Cortical Activity ◽  
Alpha Phase ◽  
Single Subject ◽  
Brain Areas ◽  
Phase Dynamics ◽  
Task Effects ◽  
Respiratory Behavior ◽  
Slow Breathing ◽  
Phase Angles

The phase of low-frequency, rhythmic cortical activity is essential for organizing brain processes because it provides a recurrent temporal frame for information coding. However, the low-frequency cortical phase exhibits great flexibility in response to external influences. Given that brain rhythms have been found to track respiratory inputs, we hypothesized that slow breathing, commonly associated with mental regulation, could reorganize the relationship between these two rhythmic systems through the adjustment of the cortical phase to such a slow train of inputs. Based on simultaneous magnetoencephalography and respiratory measurements, we report that while participants performed paced breathing, slow relative to normal breathing modulated cortical phase activity in the alpha range across widespread brain areas. Such modulation effects were specifically locked to the middle of the inspiration stage and exhibited a well-structured pattern. At the single-subject level, the phase angles underlying the effects became more likely to be diametrically opposed across breaths, indicating unique and consistent phase adjustment to slow inspiratory inputs. Neither cardiac fluctuations nor breathing-unrelated task effects could account for the findings. We suggest that slow-paced inspiration could organize the cortical phase in a regularized phase pattern, revealing a rhythmic but dynamic neural network integrated with different neurophysiological systems through volitional control. NEW & NOTEWORTHY Breathing is more complicated than a simple gas exchange, as it is integrated with numerous cognitive and emotional functions. Controlled slow breathing has often been used to regulate mental processes. This magnetoencephalography study demonstrates that slow-paced relative to normal-paced inspiration could organize the timing of alpha rhythmic activities across breathing cycles in a structured manner over widespread brain areas. Our results reveal how a volitionally controlled change in respiratory behavior could systematically modulate cortical activity.

Effect of Loading Frequency on Fatigue Crack Growth Behaviour and Microstructural Damage in P92 HAZ

2007 ◽  
Vol 120 ◽  
pp. 21-24
Author(s):  
Bum Joon Kim ◽  
Byeong Soo Lim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Low Frequency ◽  
Growth Behavior ◽  
Frequency Effect ◽  
Crack Growth Behavior ◽  
Loading Frequency ◽  
Crack Growth Behaviour ◽  
Microstructural Damage

Various hold periods in a cyclic wave of fatigue load were introduced to investigate loading frequency effects on crack growth behavior and microstructural damage. The crack growth path and microstructural damage characteristics at 600°C in tempered martensitic 9Cr-2W (P92) HAZ of welded steel were studied. Generally, low frequency effect with increasing hold periods affects microstructural damage with microvoids/cavities nucleation due to the effect of creep. Results showed that the fatigue crack growth behavior was sensitive to the loading frequency. As frequency decreased, the fatigue crack growth rate increased and the crack path mode changed from transgranular to intergranular in terms of microstructural damage. As the loading frequency decreased, it was found that the microvoids /cavities and microcracks that formed along the prior austenite grain boundaries ahead of the main crack contributed to the intergranular crack growth.

Sign in / Sign up

Export Citation Format

Share Document