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ZZ Array NEW CONCEPT

Release time:2020-08-20

ZZ-Array:


Designed For Full-Channel Systems and Inversion


ZZ-Array and Full-Channel technology are created by ZZ Resistivity Imaging Pty Ltd, Australia 


Basic principle of the resistivity method


For the resistivity method, firstly we need two electrodes (A and B) to inject current into the ground to form an electric field. When two electrodes (Figure 1) representing current electrodes at source A and sink B, inject current into the ground which has a uniform resistivity; an electric field will be formed in the half space. If multiple electrodes are placed on the surface to measure the ground’s electric potential, then a voltage curve similar to the curve in Figure 2 will be obtained.



Figure 1. Calculated electric field distribution images for a uniformly resistive background.

Figure 2. Voltage (potential) curve produced by a surface resistivity survey through a uniform medium, marking three sections: The left side of A, between A and B (AB), and the right side of B.

The medium below the surface is often not uniform, instead it can be anomalistic. For example, it may contain a high resistivity (Figure 3), thus the potential curve on the surface is no longer the same ideal form to that shown in Figure 2.  This is because the electrical field is distorted by this high resistivity . We can see this by comparing the two contours in Figure 1 and Figure 3, demonstrating that the potentials we collect on the surface contain the electric field distortion information. Therefore, we can use the collected potentials to calculate and find the underground target.  This is the basic principle of the resistivity method.

Figure 3. Electric field calculated from the same uniform background but with a relatively low resistivity anomaly in the middle.



The difference between multi-channel and multi-electrode


Currently, most resistivity instruments are multi-electrode systems, meaning there are more than 4 electrodes connected to the instrument during a survey; However, they may not be multi-channel resistivity systems.  The following diagram explains the difference between single channel, multi-channel and full-channel systems.

Figure 4. Single-channel, mutli-channel and Full-Channel data collection comparison.


Full-channel resistivity data collection


By comparing the two contours in Figure 1 and Figure 3, we can see that all potentials collected on the surface can be split into three sections: The left side of A, between A and B and the right side of B - each are distorted by the anomaly.  This means that all potentials collected from the three sections contain the distorted potential and provide useful data for later calculations.  Therefore, we should collect this information when possible.

Traditional resistivity data collection arrays such as Wenner, Schlumberger, dipole-dipole, gradient arrays, etc. (Figure 4), collect data from only one of the three sections comprising the potential surface curve (Figure 2).  For example, Wenner and Schlumberger collect data from the middle section between A and B, and the dipole-dipole array collects data from the right side of B.  The full-channel method will collect all potentials from all three sections (the left side of A, AB, and the right side of B) simultaneously.  Therefore, the full-channel method will collect much more potential information than any other arrays for each AB current injection.

Figure 5. Illustration of commonly used traditional data collection arrays.


ZZ-Array design


The ZZ-Array uses full-channel methodology, meaning it will use all electrodes (except A and B) to collect potential data from all three sections simultaneously.  For symmetry, it uses a similar principle to VES.

Supposing there are 64 electrodes in a survey, we set 60 VES central points. For each VES central point, we set N AB current injections (A and B in each pair are symmetric for the VES central point, at i*3-1, i=1 to N).  For example, for the central point at electrode 20, the first 3 AB current injection pairs are at (18,22), (15,25), and (12,28).  These 3 AB pairs are minimum for each central point in the ZZ-Array.  Furthermore, you can have the 4th AB current injection at (9,31) and the 5th at (6,34) for this central point.  A greater number of AB current injections for each central point will increase the exploration depth.

For one system with 64 electrodes, if we set 3 AB pairs for each central point, we will have a total of 162 AB current pairs * 61 voltages = 9,882 ABMN data for a surface survey using the ZZ-Array.  For 64 electrodes, we can have a maximum 330 AB current pairs with the ZZ-Array and will collect 330 * 61 = 20,130 ABMN data. For further information, please download the ZZ Universal demo data acquisition program from www.zzgeo.com and try it.


ZZ Array data example (N=4 and 64 electrodes)


ZZ surface array (N=4)

 No

A

B

Central point

ZZ surface array

1

1

5

3

ZZ surface array

2

2

6

4

ZZ surface array

3

3

7

5

ZZ surface array

4

4

8

6

...

...

 

 

 

ZZ surface array

57

57

61

59

ZZ surface array

58

58

62

60

ZZ surface array

59

59

63

61

ZZ surface array

60

60

64

62

 

 

 

 

 

ZZ surface array

61

1

11

6

ZZ surface array

62

2

12

7

ZZ surface array

63

3

13

8

ZZ surface array

64

4

14

9

ZZ surface array

65

5

15

10

...

...

 

 

 

ZZ surface array

157

43

59

51

ZZ surface array

158

44

60

52

ZZ surface array

159

45

61

53

ZZ surface array

160

46

62

54

ZZ surface array

161

47

63

55

ZZ surface array

162

48

64

56

 

 

 

 

 

ZZ surface array

163

1

23

12

ZZ surface array

164

2

24

13

ZZ surface array

165

3

25

14

...

...

 

 

 

ZZ surface array

201

39

61

50

ZZ surface array

202

40

62

51

ZZ surface array

203

41

63

52

ZZ surface array

204

42

64

53

Figure 7. example of ZZ array AB list with N=4 and 64 electrodes.

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Contact us

ZZ Resistivity Imaging Pty. Ltd.

sales@zzgeo.com

Address:Unit 3 / 239 Magill Rd, Maylands 5069  Adelaide,  South Australia

Copyright: May 2020


 

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