Laboratory Measurements Of Electrical Resistivity Research Articles

Electrical Resistivity Measurement with Spherical-Tipped Cylindrical Electrode Embedded on Two Layers.

Complex geological processes form multiple layers and change pore water chemistry, saturation level, and temperature. Eventually, the strata hinder interpreting electrical resistivity data. There are no studies that theoretically explore the effects of electrode geometries and multiple layered systems on laboratory electrical resistivity measurements. This study formulates a theoretical electrical resistance between half spherical-tipped cylindrical electrodes embedded on two horizontal layers. The electrical resistivity of each layer is considered separately in the general electrical potential equation with different equipotential surface areas. The finite element analysis is conducted to validate the theoretical equation. Further interpretation provides insights into the distribution of electrical current flow under electrical resistivity mismatch for discussion.

Theoretical Study on Geometries of Electrodes in Laboratory Electrical Resistivity Measurement

Electrical resistivity tests have been widely conducted in multiple scales, from a few centimeters to kilometers. While electrode spacing is used to define field resistance, laboratory measurements in a limited space need to consider electrode geometry. However, there are no studies that theoretically explore the effects of the geometries of electrodes and container size on laboratory electrical resistivity measurements. This study formulates a theoretical electrical resistance for the geometry of cylindrical electrodes and the size of a non-conductive container with the method of image charges. As a complementary study, experimental tests were conducted to verify the derived equations. The discussion includes the concepts of the spherical equivalent electrodes and a simple design method for container size.

Electrical resistivity as a binary classifier for bridge scour evaluation

Scour is responsible for approximately 60% of all bridge collapses in the United States. Evaluating scour using empirical equations has proven inaccurate, particularly in fine-grained soils. Furthermore, evaluating scour potential based on site specific erosion testing can be uneconomic as erosion testing is time consuming. Many soil characteristics that affect soil erosion also influence soil electrical resistivity (ER) which can be measured in the field or in the laboratory. The objectives of this study were to assess if field and laboratory ER measurements can be used interchangeably for characterizing soil erodibility and the impact of saturation as expected during a flood event, on the ER based soil erodibility model. Twenty-one bridge sites were used for in situ electrical resistivity tomography (ERT) surveys and erosion testing. Supplementary ER measurements at varying degrees of saturation were also conducted using a soil box in the laboratory. It was found that ER values do not differ significantly when ERT is conducted on streambanks as opposed to fully saturated conditions. A receiver operating characteristic curve and probability density function (PDF) were used to determine that soils with ER over 50 Ωm had an 87% probability of classifying as highly erodible based on this data set. Statistical tests also suggested that laboratory ER can be used as an alternative to field ERT surveys. While in situ ERT provides more information in terms of spatial variation in the subsurface, laboratory ER measurements on retrieved samples will allow transportation agencies to utilize the developed erodibility classifier model without the capital investment of an ERT system. Given the large number of bridges with scour susceptible foundations in the National Bridge Inventory, ER can be used to rapidly prioritize them for additional testing to measure the erosion potential or to characterize the soil erosion at proposed bridge sites.

Simple and multiple regression models for relationship between electrical resistivity and various soil properties for soil characterization

Precise determination of engineering properties of soil is essential for proper design and successful construction of any structure. The conventional methods for determination of engineering properties are invasive, costly and time-consuming. Electrical resistivity survey is an attractive tool for delineate subsurface properties without soil disturbance. Reliable correlations between electrical resistivity and other soil properties will enable us to characterize the subsurface soil without borehole sampling. This paper presents the correlations of electrical resistivity with various properties of soil. Soil investigations, field electrical resistivity survey and laboratory electrical resistivity measurements were conducted. The results from electrical resistivity tests (field and laboratory) and laboratory tests were analyzed together to understand the interrelation between electrical resistivity and various soil properties. The test results were evaluated using simple and multiple regression analysis. From the data analysis, significant quantitative and qualitative correlations have been obtained between resistivity and moisture content, friction angle and plasticity index. Weaker correlations have been observed for cohesion, unit weight of soil and effective size (D 10).

Electrical Resistivity Based Non-Destructive Testing Method for Determination of Soil’s Strength Properties

Precise determination of engineering properties of soil is essential for proper design and successful construction of any structure. The conventional methods for determination of engineering properties are invasive, costly and time-consuming. Electrical resistivity survey is an attractive tool for delineating subsurface properties without soil disturbance. Reliable correlations between electrical resistivity and other soil properties will enable us to characterize the subsurface soil without borehole sampling. This paper presents the preliminary results of an ongoing research on correlations of electrical resistivity with strength properties of soil. Soil investigations, field electrical resistivity survey (VES) and laboratory electrical resistivity measurements were conducted. From the data analysis, significant correlations have been obtained between resistivity and moisture content and angle of internal friction. Weaker correlations have been observed for cohesion and unit weight of soil.

Integrating Geo-Electrical and Geotechnical Data for Soil Characterization

Precise determination of engineering properties of soil is essential for proper design and successful construction of any structure. The conventional methods for determination of engineering properties are invasive, costly and time-consuming. Electrical resistivity survey is an attractive tool for delineating subsurface properties without soil disturbance. Reliable correlations between electrical resistivity and other soil properties will enable us to characterize the subsurface soil without borehole sampling. This paper presents the preliminary results of an ongoing research on correlations of electrical resistivity with strength properties of soil. Soil investigations, field electrical resistivity survey (VES) and laboratory electrical resistivity measurements were conducted. From the data analysis, significant correlations have been obtained between resistivity and moisture content and angle of internal friction. Weaker correlations have been observed for cohesion and unit weight of soil.

The relationship between silica diagenesis and physical properties in the East/Japan Sea: ODP Legs 127/128

Six sites were drilled on ODP Legs 127 and 128. One of the significant results of this drilling was the detection of an opal amorphous silica (opal-A) and opal cristobalite (opal-CT) transformation at all the drill sites. Laboratory measurements of electrical resistivity and physical properties (e.g., velocity, porosity, and density) were conducted on the sediments and rocks sampled from the four sites (Sites 794, 795, 796, and 797). Electrical resistivity and physical properties data show significant change at the opal-A/opal-CT and the opal-CT/Quartz boundaries, suggesting the effects of silica diagenesis. Electrical resistivity reflects the change of physical properties (esp., velocity, wet bulk density, and porosity) well throughout the sites. The transformation boundary is easily recognized in the electrical and physical properties. Electrical resistivity increases by about 50% and 950% across the opal-A/opal-CT and opal-CT/Quartz boundaries, respectively. Thus, electrical resistivity as well as physical properties may be used to identify lithology and diagenetic boundaries such as opal-A/CT, opal-CT/Quartz, and to estimate the reservoir character (e.g., permeability and pore geometry) of sediments and rocks.

Laboratory measurements of electrical resistivity at reservoir conditions : Mahmood, S M; Maerefat, N L; Chang, M M SPE Form EvalV6, N3, Sept 1991, P291–300

Laboratory measurements of electrical resistivity at reservoir conditions : Mahmood, S M; Maerefat, N L; Chang, M M SPE Form EvalV6, N3, Sept 1991, P291–300

Influence of diagenesis on the electrical resistivity and the formation factor of deep-sea carbonate sediments

Laboratory measurements of electrical resistivity on two DSDP pelagic carbonate sequences permitted the study of the effect of diagenesis on the electrical and other physical properties such as velocity and porosity. Electrical resistivity and formation factor increase with sediment depth. Changes in porosity with progressive diagenesis (that is, ooze-chalk-limestone) are observed, and changes in pore geometry are inferred. These changes are interpreted in terms of systematic variations in electrical and physical properties. Influence of silica on carbonate diagenesis may result in significant change in pore geometry. This effect inhibits electrical conduction leading to complicated but generally high resistivity values for siliceous and cherty limestones. Compressional velocity correlates well with resistivity for both sequences.

Laboratory‐determined transport properties of Berea sandstone

We report laboratory measurements of electrical resistivity ρ, water permeability k, and compressional wave velocity [Formula: see text] for both intact and fractured Berea sandstone samples as functions of temperature from 20°C to 200°C and effective pressure [Formula: see text] from 2.5 MPa to 50 MPa. For the intact sample, [Formula: see text] increases from 3.52 km/s to 4.16 km/s as [Formula: see text] goes from 3 to 50 MPa. With increasing temperature, [Formula: see text] decreases at rates of about 3 percent per 100°C at [Formula: see text] of 5 MPa and about 1.5 percent per 100°C at [Formula: see text] of 38 MPa. Data from the fractured sample are qualitatively similar, but velocities are about 10 percent lower. For both intact and fractured samples, ρ increases less than 15 percent as [Formula: see text] increases from 2.5 MPa to 50 MPa. Although both samples show a larger decrease in resistivity with increasing temperature, most of this change is attributed to the decrease in resistivity of the pore fluid over that temperature range. For both samples, k decreases with increasing pressure and temperature. The intact sample permeability varies from 23 mD at 3 MPa and 20°C to less than 1 mD at 50 MPa and 150°C. The permeability of the fractured sample varies from 676 mD at 3 MPa and 20°C to less than 1 mD at 40 MPa and 190°C. The effect of the fracture on k vanishes after several pressure cycles and above about 100°C. These laboratory data are used to demonstrate the possibility of using resistivity and velocity measurements to estimate in‐situ permeability of a reservoir.

Electromechanical phenomena associated with earthquakes

This article reviews the field, laboratory, and theoretical investigations made concerning different electromechanical phenomena associated with earthquakes. It discusses laboratory measurements of electrical resistivity of rocks stressed up to fracture, particular attention being paid to the interpretation of results according to the diffusion-dilatancy theory. This is followed by the discussion of field measurements of electrical characteristics of rocks in seismic areas in connections with seismic activity in these regions. Piezoelectric and electrostrictive phenomena are briefly discussed, and also a theoretical model of electro-elastic effects associated with an earthquake source. The last part concerns electrokinetic phenomena in porous rocks, caused by the diffusion of fluids into the dilatant focal region. The divergence of opinion about the physical models of the earthquake process is emphasized.

Laboratory measurements of electrical resistivity, polarizability and phase angle spectra of sulphide bearing rocks from captains flat N.S.W.

Measured resistivities of sphalerite – galena – pyrite ores evince an inverse correlation with metallic mineral concentration whereas induced polarization parameters show a positive correlation. The resistivity of massive sulphide ore appears much greater than that of constituent minerals suggesting limited usefulness of geophysical methods which locate electrical conductors. The high polarizability of concentrated ores corroborates the applicability of induced polarization for locating massive sulphide deposits. The low resistivity and high polarizability of zinc rich samples suggest that sphalerite may contribute significantly to the electrical properties of lead–zinc–silver ores. Laboratory measurements of phase angle spectra suggest that this parameter may be of diagnostic value in surface and downhole variable frequency I.P. surveying.

Electrical Conductivities in Oil-Bearing Shaly Sands

ABSTRACT A simple physical model was used to develop an equation that relates the electrical conductivity of a water-saturated shaly sand to the water conductivity and the cation- exchange capacity per unit pore volume of the rock. This equation fits both the experimental data of Hill and Milburn and data obtained recently on selected shaly sands with a wide range of cation-exchange capacities. This model was extended to cases where both oil and water are present in the shaly sand. This results in an additional expression, relating the resistivity ratio to water saturation, water conductivity and cation-exchange capacity per unit pore volume. The effect of shale content on the resistivity index- water saturation function is demonstrated by several numerical examples. INTRODUCTION A principal aim of well logging is to provide quantitative information concerning porosity and oil saturation of the permeable formations penetrated by the borehole. For clean sands, the relationships between measured physical quantities and porosity or saturation are well known. However, the presence of clay minerals greatly complicates log interpretation, particularly the electrical resistivity and SP logs, and considerably affects evaluation of hydrocarbon-bearing formations. The conductance and electrochemical behavior of shaly sands and their relation to log interpretation have been studied by many workers. Wyllie and Lynch reviewed this work in some detail. Virtually all laboratory measurements of electrical resistivity and electrochemical potential of shaly sands published to date are the work of Hill and Milburn.