A MODIFIED PSEUDOSECTION FOR RESISTIVITY AND IP PDF

Dipole--dipole induced-polarization measurements are commonly presented as pseudosections, but results using different dipole lengths cannot be combined into a single pseudosection. By considering the theoretical results for simple earth models, a unique set of relative depth coefficients is empirically derived, such that measurements with different array parameters will ''mesh'' smoothly into a combined pseudosection. Application of these coefficients to a number of theoretical and field cases shows that they give reasonable results when applied to more complicated models. The empirical coefficients are compared with Roy's theory of ''depth of investigation characteristic,'' and support that theory, if a modified definition of ''effective depth'' is accepted.

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Electrode arrays can be defined as various arrangements of electrodes used to perform geophysical resistivity measurements. These arrays were developed before computers and modern algorithms were available in order to make field measurements more efficient and data interpretation easier. There are a number of different arrays, but only a few have been important and frequently used.

These include the Schlumberger array, the Wenner array, and the dipole-dipole array. Other less commonly used arrays are pole-dipole, pole-pole, square, bipole-bipole, equatorial, gradient, and azimuthal.

The Wenner array was invented by an American physicist named Frank Wenner Because the field crew only needs to consider an equal electrode spacing for all four electrodes makes the Wenner method accessible to a non-technical field crew to perform. The Wenner array can be used for profiling also known as electrical trenching or for vertical electrical sounding also known as VES or electrical drilling , and there are benefits and drawbacks for each.

The advantage of the Wenner method is apparent when you perform a profiling survey, because in this implementation you will move only one electrode for each measurement. When the Wenner array then moves over a fracture, it could indicate a low-resistive area, thus indicating the presence of water. The Schlumberger array was named for Conrad Schlumberger, the founder of the modern-day Schlumberger oilfield services company and pioneer of electrical methods in the early s.

During this period, both the Schlumberger and Wenner arrays were used extensively for mineral and groundwater exploration. Most arrays use four electrodes: two current electrodes that inject the current into the ground, and two electrodes that measure the resulting potential. In the Schlumberger array, the four electrodes are placed in a line, centered around a midpoint.

The two outer electrodes are the current electrodes and the two inner electrodes are the potential electrodes. Schlumberger is the best method used for vertical electrical sounding for practical reasons. It is less labor-intensive than the Wenner array see below because you only need to move the two transmitting electrodes for each new reading, whereas the Wenner requires moving all four electrodes for each new measurement.

The dipole-dipole array, consisting of a current electrode pair and a potential electrode pair, was originally used for mineral exploration with the induced polarization IP method. The values are then contoured and colorized to represent a rough image of the subsurface. When compared to the Wenner array, which provides a big picture, the dipole-dipole array provides great detail. The Pole-Dipole array is similar to the Schlumberger Array in that the receiver dipole is a tenth of the size of the transmitter dipole electrodes A and B.

Unlike the Schlumberger array, with the Pole-Dipole array, when measuring in the center of the transmitting dipole the receiver is moved outside the transmitter dipole and beyond. The B-electrode is considered to be at a mathematical infinity when it is at a distance of beyond times the size of the survey area of the receiver dipole.

After placing the remote B-electrode at infinity, you then move the potential electrodes the receiver dipole; electrodes M and N to a position one dipole spacing away from the current A-electrode and take a reading.

Then the receiver dipole is moved one additional dipole size away from the A-electrode, and another reading is taken. This continues until you begin losing signal between the current and the potential electrodes. The pole-dipole array is preferred to the Dipole-Dipole array when it comes to depth penetration, since depth is related to the distance that separates the A-electrode and the M-electrode.

Between dipole-dipole, pole-dipole, and pole-pole, the latter is the least common. It is only used when you need to see extremely deep in the ground at the additional logistics of placing two remote electrodes at infinity twenty times that of the survey area. To use the pole-pole survey, you set up the electrodes like you would in a pole-dipole survey—but one of the potential electrodes is placed at infinity in the opposite direction, so one electrode is on each side of the survey area.

You then proceed exactly as you would with pole-dipole: The current electrode stay in the same place and the potential electrode move out to take new readings. The primary issue with using the pole-pole array is space. For example, if the survey area is meters in length, the remote electrodes B and N would need to be placed at a distance of at least twenty times the survey area.

The two infinity electrodes would then be at least meters apart. You also have to consider traffic that could run over your remote electrode cables, creeks, or brush when handling the remote wire. The equatorial array consists of the two dipoles—A-B and M-N—oriented perpendicular to the survey line and parallel to each other.

The advantage of the equatorial array is that you are able to penetrate deeper into the ground than when using the dipole-dipole array, assuming the length along the survey line is the same.

This can be particularly advantageous when pulling an array of electrodes behind a vehicle or in limited spaces. The square array is a special case of the equatorial array, named because the electrodes form the shape of a square and the sides of the array are all equal length.

This array is used most frequently in determining the anisotropy i. Instead of expanding the electrodes, the square is turned typically 15 degrees for each measurement around the center point of the square.

Taking a number of readings through the square array, he can determine which direction is more conductive and thus the main direction of the fractures. Furthermore, if you needed to see deeper to gain more information on the fractures in the rock body, you could expand the size of the square and repeat the same procedure. It may, for instance, show that the fracture changes direction at a particular depth. The gradient array is used to measure the potential using a dipole M-N moving between two fixed current electrodes A and B.

The array is used to map the electrical field caused by the two fixed current electrodes. The Schlumberger array is a variation of the gradient array. The gradient array is easy to use with a multichannel resistivity system, because you can take several simultaneous measurements with the different potential electrode pairs at different locations. It permits also different sets of multiple gradient measurements which are made with the current electrodes at different locations.

The azimuthal method is actually less of an array and more of an electrode orientation. For example, you may measure with either a Wenner array or Schlumberger array in order to determine the resistivity of a formation in a certain direction as described for the square array.

When your current electrodes are at and you take the first reading. Evaluation of this data will give you information about fracture patterns in the formation below. It primarily uses the pole-dipole array to delineate an ore body. One current electrode is placed at infinity and the other current electrode is placed in contact with the ore body at an outcrop or in a borehole.

The two potential electrodes are used as a dipole to measure the electrical gradient in a profile or grid on the surface.

By drawing a contour map of the data, the outline of the ore body can be displayed. The word bipole is used instead of dipole when the two transmitting electrodes are placed so far apart that the electric field from them can be considered a field from two separate poles. In other words, the distance between the receiver and transmitter dipoles is small in relation to the dipoles themselves. Note: Strictly speaking, the field from the transmitting electrodes when using the dipole-dipole array is actually the field from a bipole especially as it pertains to the measurements closest to the transmitting electrodes.

However, this is labeled as a dipole-dipole array. We would love to discuss any comments or questions you have. Skip to main content. Schlumberger Array The Schlumberger array was named for Conrad Schlumberger, the founder of the modern-day Schlumberger oilfield services company and pioneer of electrical methods in the early s.

Dipole-Dipole Array The dipole-dipole array, consisting of a current electrode pair and a potential electrode pair, was originally used for mineral exploration with the induced polarization IP method. Pole-Dipole Array The Pole-Dipole array is similar to the Schlumberger Array in that the receiver dipole is a tenth of the size of the transmitter dipole electrodes A and B.

Pole-Pole Array Between dipole-dipole, pole-dipole, and pole-pole, the latter is the least common. Equatorial Array The equatorial array consists of the two dipoles—A-B and M-N—oriented perpendicular to the survey line and parallel to each other. Square Array The square array is a special case of the equatorial array, named because the electrodes form the shape of a square and the sides of the array are all equal length. Gradient Array The gradient array is used to measure the potential using a dipole M-N moving between two fixed current electrodes A and B.

Bipole-Bipole Array The word bipole is used instead of dipole when the two transmitting electrodes are placed so far apart that the electric field from them can be considered a field from two separate poles.

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A MODIFIED PSEUDOSECTION FOR RESISTIVITY AND IP

We'd like to understand how you use our websites in order to improve them. Register your interest. Following the depths of investigation of different electrode arrays, given by Roy and Apparao and Roy , a modified pseudo-depth section was suggested for any array by Apparao and Sarma as a tool in resistivity and IP prospecting. The tool was used for the interpretation of IP and resistivity anomalies obtained in a virgin area—Jonnagiri village, Pattikonda Taluq, Kurnool district A. Two of the four bore holes recommended encountered sulphide mineralization, while the other two met with white altered ashy material at the position of the maximum anomaly contour in the depth sections.

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The modified pseudo-depth section as a tool in resistivity and IP prospecting — A case history

Electrode arrays can be defined as various arrangements of electrodes used to perform geophysical resistivity measurements. These arrays were developed before computers and modern algorithms were available in order to make field measurements more efficient and data interpretation easier. There are a number of different arrays, but only a few have been important and frequently used. These include the Schlumberger array, the Wenner array, and the dipole-dipole array. Other less commonly used arrays are pole-dipole, pole-pole, square, bipole-bipole, equatorial, gradient, and azimuthal.

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A modified pseudosection for resistivity and IP

On: A modified pseudosection for resistivity and Ip by L. Edwards G Eophysics , August , p. Geophysics 43 6 : , Improvements to the Zohdy Method for the inversion of resistivity sounding and pseudosection data.

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