**4.3 Electrical methods**

*Magnetometers - Fundamentals and Applications of Magnetism*

ing at depth with permeability.

*shown. NF, not fractured; F, fractured.*

Two of the sections had NW-SE orientation and two NE–SW (**Figure 9**) with

The magnetic section 1 **(Figure 10**) displays four terrestrial magnetic domains (TMD): first station 0 to 54 was characterized by a series of magnetic anomalies related to short wavelengths (20–40 m), high frequencies and amplitudes of 160 nT. It was geologically correlated with a highly fractured zone, while the horizontal gradients give values of up to 11 nT/m. Second, TMD 2 is located between stations 55 and 78, and it is defined by presenting a normal magnetic field, where no abnormal areas are observed. Third TMD 3 is located between stations 79 and 87 and shows an anomalous zone limited by two magnetic anomalies that have amplitudes of 33 and 65 nT and horizontal gradients of 2.6 and 6 nT/m, respectively. Geologically, it is correlated with an area of medium fracture possibilities. The last, TMD 4 is limited between stations 88 and 135, in general it shows a discretely disturbed magnetic field where it is not considered with the possibility of associat-

The magnetic section 2 is located towards the E portion of La Dulcita (**Figure 9**), it presents five TMD's (**Figure 11**), the first one limited between stations 0 and 32 shows a normal behavior of the RMF, where magnetic anomalies are distinguished.

*Ground magnetic profile 1, with a NW-SE orientation. At the upper part, the residual magnetic field (RMF) is plotted (red); the horizontal gradient of the RMF is plotted at the lower part (blue), and at the bottom a qualitative interpretation of the percentage of probabilities of association with fracturing in the underground is* 

*Ground magnetic profile 2, with a NE–SW orientation. At the upper part the residual magnetic field (RMF) is plotted (red); the horizontal gradient of the RMF is plotted at the lower part (blue), and at the bottom a qualitative interpretation of the percentage of probabilities of association with fracturing in the underground is* 

*shown. HF, highly fractured; LF, light fractured; NF , not fractured.*

the population of La Dulcita being in the central part of these profiles.

**36**

**Figure 11.**

**Figure 10.**

Two electrical sections (or profiles) of apparent resistivity, induced polarization and self-potential were made with the Schlumberger type electrode array (**Figure 14**), using two electrode spacings AB/2 = 100 and 200 m and a Syscal R-2 resistivity instrumental (**Figure 15**). The sections were made in the same directions as the magnetic profiles 1 and 2, which were showed more possibilities of associating with fracturing in the underground.

#### **Figure 12.**

*Ground magnetic profile 3, with a NE–SW orientation. At the upper part the residual magnetic field (RMF) is plotted (red); the horizontal gradient of the RMF is plotted in the lower part (blue), and at the bottom qualitative interpretation of the percentage of probabilities of association with fracturing in the underground is shown. F, fractured; NF, not fractured.*

#### **Figure 13.**

*Ground magnetic profile 4, with a NW-SE orientation. At the upper part the residual magnetic field (RMF) is plotted (red); the horizontal gradient of the RMF is plotted at the lower part and at the bottom a qualitative interpretation of the percentage of probabilities of association with fracturing in the underground is shown. NF, not fractured.*

#### **Figure 14.**

*The Schlumberger electrode array diagram, used for the realization of vertical electric sections and soundings (VES). The maximum openings of the VES were AB/2 of 1500 and 2000 m.*

The W-E electrical profile shows in general an increase in resistivity with depth except two areas, from station 400 to 500 and 750 where the conductivity is higher. The induced polarization in these profiles generally shows a decrease in chargeability, except for two areas of station 450–500 and 750, where the load capacity tends to increase. The spontaneous potential is observed to decrease in general with larger separations of AB/2 (**Figure 16**).

The S-N electrical section, presents values of apparent resistivity lower at depth for the most part, except from station 450 to 550 where there is a small increase in resistivity to separations greater than AB/2. The chargeability values in the induced polarization are observed in contrast throughout the section, increase to greater separations of AB/2 in the areas of station 0–150, 350, 550–900 and in the station 1100. The spontaneous potential (SP) in this section behaves similarly to both

**39**

**Figure 16.**

**Figure 15.**

*4.3.1 Vertical electrical soundings*

*The Magnetometry—A Primary Tool in the Prospection of Underground Water*

electrode separations between stations 0 and 550, where at higher separations of AB/2, the values (mV) increase slightly from station 600 to 900, the values decrease for AB/2 = 200 m and from station 950 to 1300, the SP is changing (**Figure 17**).

*frequencies (fracture, permeability) in profile 1 (Figure 10) of magnetometry.*

*Electrical profile 1, with a NW-SE orientation, where (a) the apparent resistivity is plotted; in (b) the induced polarization and in (c) the self-potential. These electrical profiles were located on the zones showing high* 

Five vertical electric soundings (VES') were made with maximum openings of the current electrodes (AB/2) of 1500 and 2000 m, four of them are located in identified zones (magnetometry) with possibilities of associating depth

*DOI: http://dx.doi.org/10.5772/intechopen.84322*

*Electrical instruments used for vertical electric soundings and sections.*

*The Magnetometry—A Primary Tool in the Prospection of Underground Water DOI: http://dx.doi.org/10.5772/intechopen.84322*

#### **Figure 15.** *Electrical instruments used for vertical electric soundings and sections.*

#### **Figure 16.**

*Magnetometers - Fundamentals and Applications of Magnetism*

The W-E electrical profile shows in general an increase in resistivity with depth except two areas, from station 400 to 500 and 750 where the conductivity is higher. The induced polarization in these profiles generally shows a decrease in chargeability, except for two areas of station 450–500 and 750, where the load capacity tends to increase. The spontaneous potential is observed to decrease in general with larger

*The Schlumberger electrode array diagram, used for the realization of vertical electric sections and soundings* 

*Ground magnetic profile 4, with a NW-SE orientation. At the upper part the residual magnetic field (RMF) is plotted (red); the horizontal gradient of the RMF is plotted at the lower part and at the bottom a qualitative interpretation of the percentage of probabilities of association with fracturing in the underground is shown.* 

*(VES). The maximum openings of the VES were AB/2 of 1500 and 2000 m.*

The S-N electrical section, presents values of apparent resistivity lower at depth for the most part, except from station 450 to 550 where there is a small increase in resistivity to separations greater than AB/2. The chargeability values in the induced polarization are observed in contrast throughout the section, increase to greater separations of AB/2 in the areas of station 0–150, 350, 550–900 and in the station 1100. The spontaneous potential (SP) in this section behaves similarly to both

**38**

**Figure 14.**

**Figure 13.**

*NF, not fractured.*

separations of AB/2 (**Figure 16**).

*Electrical profile 1, with a NW-SE orientation, where (a) the apparent resistivity is plotted; in (b) the induced polarization and in (c) the self-potential. These electrical profiles were located on the zones showing high frequencies (fracture, permeability) in profile 1 (Figure 10) of magnetometry.*

electrode separations between stations 0 and 550, where at higher separations of AB/2, the values (mV) increase slightly from station 600 to 900, the values decrease for AB/2 = 200 m and from station 950 to 1300, the SP is changing (**Figure 17**).

### *4.3.1 Vertical electrical soundings*

Five vertical electric soundings (VES') were made with maximum openings of the current electrodes (AB/2) of 1500 and 2000 m, four of them are located in identified zones (magnetometry) with possibilities of associating depth

*Electrical section 2, with a NE–SW orientation, where (a) the apparent resistivity is plotted; in (b) the induced polarization and in (c) the self-potential. It is located on the magnetic section 2.*

#### **Figure 18.**

*Graphs of vertical electric soundings (VES) 1 and 2 and their comparison with VES 4, related to a well with an expenditure of the order of 25 L/s. note the thickness (170.4 m) correlated with the aquifer horizon (28.7 Ωm) possibly due to a sandy unit, overlying a clay horizon (2 Ωm).*

permeability. One of the SEVs was carried out on a producer well that was located 2.3 km SW of La Dulcita and geologically located in the zone of the sunken block and aeromagnetically associated with the AMD I, which served as calibrator for the interpretations.

**41**

HKH (VES 3).

**Figure 19.**

(**Figures 18** and **19**).

**5. Results and conclusions**

*The Magnetometry—A Primary Tool in the Prospection of Underground Water*

The qualitative interpretation of the VES' morphology showed that the producer was well associated with a KQH curve (VES 4), among four remaining SEVs two were from the QQH family (VES 2 and 5), one was HKQH (VES 1) and the other

*Graphs of the vertical electric soundings (VES) 3 and 5 and its comparison with the VES 4, related to a well, with an yield of the order of 16 L/s. Note that VES 3 shows a sequence of geological units (~ 53 Ωm) confined by* 

*clay horizons (3–4 Ωm), while VES 5 shows a decrease in resistivity to depths of the order of 700 m.*

The VES' were processed and interpreted with the commercial program Resix Plus that solves the inverse problem based on the Ghosh method of the inverse filter [22]. Each of the VES was compared with the VES (4) of the producing well

**Figure 18** indicates that the data interpreted in the VES 4 (KQH) for producing well and calibrator clearly indicates that at the base of the aquifer there is a clay unit (2 Ωm) and correlates with the resistivity of 28.69 Ωm with a thickness of 170.4 m, hence the well produces about 16 L/s. In this comparison, the VES 1 (HKQH) shows a horizon (23.23 Ωm) with a thickness of 33.5 m, possibly associating a sandy unit with moisture content at a depth of the order of 24 m. The VES 2 (QQH) shows a unit with

a resistivity of 18.65 Ωm at a depth of less than 3 m with a thickness of 30 m.

**Figure 19** shows the results of interpreting the VES' 3 and 5, they are also compared with the VES 4 (well). The VES 3 (HKH) shows the existence of a geological unit (53.20 Ωm) bordered by two clay horizons (4 and 3 Ωm) at a depth of the order of 61 m and a thickness of 34 m. It presents very good resistive contrast and the unit can be a fractured basalt horizon. VES 5 (QQH) shows a horizon possibly associated with a clay-sandy unit (14.8 Ωm) at a depth of 15 m and a thickness of 29 m. A large layer (> 700 m) of clay (9.2 Ωm) that starts to make an interpretation at a depth of 45 m.

Once the information was interpreted and analyzed, in some areas and communal land holding close to La Dulcita, a zone that meets the standards that are associated to the aquifer were found. It aeromagnetically shows the existence of alignments in N-S and E-W orientation and their location on top of the graben

*DOI: http://dx.doi.org/10.5772/intechopen.84322*

*The Magnetometry—A Primary Tool in the Prospection of Underground Water DOI: http://dx.doi.org/10.5772/intechopen.84322*


#### **Figure 19.**

*Magnetometers - Fundamentals and Applications of Magnetism*

*Electrical section 2, with a NE–SW orientation, where (a) the apparent resistivity is plotted; in (b) the* 

permeability. One of the SEVs was carried out on a producer well that was located 2.3 km SW of La Dulcita and geologically located in the zone of the sunken block and aeromagnetically associated with the AMD I, which served as calibrator for the

*Graphs of vertical electric soundings (VES) 1 and 2 and their comparison with VES 4, related to a well with an expenditure of the order of 25 L/s. note the thickness (170.4 m) correlated with the aquifer horizon* 

*(28.7 Ωm) possibly due to a sandy unit, overlying a clay horizon (2 Ωm).*

*induced polarization and in (c) the self-potential. It is located on the magnetic section 2.*

**40**

interpretations.

**Figure 18.**

**Figure 17.**

*Graphs of the vertical electric soundings (VES) 3 and 5 and its comparison with the VES 4, related to a well, with an yield of the order of 16 L/s. Note that VES 3 shows a sequence of geological units (~ 53 Ωm) confined by clay horizons (3–4 Ωm), while VES 5 shows a decrease in resistivity to depths of the order of 700 m.*

The qualitative interpretation of the VES' morphology showed that the producer was well associated with a KQH curve (VES 4), among four remaining SEVs two were from the QQH family (VES 2 and 5), one was HKQH (VES 1) and the other HKH (VES 3).

The VES' were processed and interpreted with the commercial program Resix Plus that solves the inverse problem based on the Ghosh method of the inverse filter [22]. Each of the VES was compared with the VES (4) of the producing well (**Figures 18** and **19**).

**Figure 18** indicates that the data interpreted in the VES 4 (KQH) for producing well and calibrator clearly indicates that at the base of the aquifer there is a clay unit (2 Ωm) and correlates with the resistivity of 28.69 Ωm with a thickness of 170.4 m, hence the well produces about 16 L/s. In this comparison, the VES 1 (HKQH) shows a horizon (23.23 Ωm) with a thickness of 33.5 m, possibly associating a sandy unit with moisture content at a depth of the order of 24 m. The VES 2 (QQH) shows a unit with a resistivity of 18.65 Ωm at a depth of less than 3 m with a thickness of 30 m.

**Figure 19** shows the results of interpreting the VES' 3 and 5, they are also compared with the VES 4 (well). The VES 3 (HKH) shows the existence of a geological unit (53.20 Ωm) bordered by two clay horizons (4 and 3 Ωm) at a depth of the order of 61 m and a thickness of 34 m. It presents very good resistive contrast and the unit can be a fractured basalt horizon. VES 5 (QQH) shows a horizon possibly associated with a clay-sandy unit (14.8 Ωm) at a depth of 15 m and a thickness of 29 m. A large layer (> 700 m) of clay (9.2 Ωm) that starts to make an interpretation at a depth of 45 m.

## **5. Results and conclusions**

Once the information was interpreted and analyzed, in some areas and communal land holding close to La Dulcita, a zone that meets the standards that are associated to the aquifer were found. It aeromagnetically shows the existence of alignments in N-S and E-W orientation and their location on top of the graben

**Figure 20.**

*The graphs that support the existence of a fractured area and with humidity in the underground are shown. The magnetism intensity graph (a) shows a clearly fractured zone towards the NW portion of the section. In the geoelectric profile (B), a contrast in resistivity is observed towards station 400, it decreases to openings of AB/2 = 200 m with respect to AB/2 = 100 m. the SEV 3 (C) shows association with type H curves.*

structure. It is represented in an aeromagnetic map by the magnetic lows (blue color) the pit area and magnetic highs (color red). Thus, La Dulcita area is located in the limits of three aeromagnetic domains, which already indicates in ground magnetic measurements and should necessarily have a magnetic susceptibility contrast that will be reflected with significant differences in the amplitude of the magnetic field.

The ground magnetic sections indicate the zones that can be associated with permeability and the zones that do not have association with this physical property. The magnet simile is parameter for the interpretation of fracture in the underground. It will generate a simple anomaly if not related with fracture and provide a series of anomalies, which will be characterized by high frequencies. The calculation of the horizontal gradient of the magnetic field is completely resolutive to be able to observe fractured (permeable) zones of relatively healthy zones. In the magnetic section 1, the different physical behaviors that exist in the underground are clearly shown in the first portion of a highly fractured area contrasted with the rest of the section, which indicates that the magnetic susceptibilities of each terrestrial magnetic domains are associated with different units.

With the aerial and terrestrial magnetism, it was easy to find areas with high possibilities of being associated with fracturing (permeability).

With the electrical sections, it was possible to quickly scan the areas with possibilities of being associated with permeability and verify if they could also be associated with humidity. Producer well is key to facilitating the interpretation of vertical electric soundings, which in order to be associated with humidity should have as part of their morphology a portion type H.

In the area that was most likely to be associated with permeability and humidity in the underground (**Figure 20**) where a drilling was carried out by the State Water

**43**

**Author details**

wells.

**Acknowledgements**

Héctor López Loera

Geosciences Department, San Luis Potosí, México

provided the original work is properly cited.

\*Address all correspondence to: hlopezl@ipicyt.edu.mx

Instituto Potosino de Investigación Científica y Tecnológica A.C. (IPICYT), Applied

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*The Magnetometry—A Primary Tool in the Prospection of Underground Water*

Commission of San Luis Potosí, with production of 4 L/s. Furthermore, if we take into account the previously three dry wells, which had been drilled then it can be

With the help of the above methodology, the trained eye of the field geologist is strengthened with this methodology that uses scientific instruments, whose function is to detect the variation in the physical properties. For example, the magnetic susceptibility and resistivity of the rocks that are hidden below the Surface. Undoubtedly, the usage will certainly increase the percentage of successful drilled

This work was funded by the State Water Commission, San Luis Potosí and COPOCYT-SLP. My sincere gratitude goes to Ing. Víctor J. Martínez Ruíz for his support to drawing geological map. I also thank David E. Torres Gaytán for his contribution in the preparation of this work. Also my sincere gratitude to Dr., Sanjeet

Lumar Verna and Lucia Aldana Navarro for their comments on writing.

*DOI: http://dx.doi.org/10.5772/intechopen.84322*

said that this methodology has met the objective.

*The Magnetometry—A Primary Tool in the Prospection of Underground Water DOI: http://dx.doi.org/10.5772/intechopen.84322*

Commission of San Luis Potosí, with production of 4 L/s. Furthermore, if we take into account the previously three dry wells, which had been drilled then it can be said that this methodology has met the objective.

With the help of the above methodology, the trained eye of the field geologist is strengthened with this methodology that uses scientific instruments, whose function is to detect the variation in the physical properties. For example, the magnetic susceptibility and resistivity of the rocks that are hidden below the Surface. Undoubtedly, the usage will certainly increase the percentage of successful drilled wells.
