Resistivity Zone Research Articles

Potential Aquifer Exploration using Electrical Resistivity Imaging at Rumbio Jaya, Kampar, Riau

Groundwater sustainability has become a serious issue as a water resource needed by society. Therefore, electrical Resistivity Imaging was carried out at Rumbio Jaya, Kampar, and Riau to study groundwater aquifer's electrical characteristics. The equipment used is a Geocis resistivity meter with (32) multi-electrodes alignment. Wenner configuration electrode was applied in this survey. The 2-D Electrical Resistivity inversion results indicate there are three resistivity zones; (1) Low resistivity value (0.0093 – 4.84 Ωm) representing conductive clay; (2) intermediate resistivity value (1.07 – 171 Ωm) indicate as potential aquifer layer; and (3) a high resistivity value (61 – 4000 Ωm) occupying as bolder of rock. All the zones have different thicknesses and depths, but mostly clay layers dan boulders are shown as lenses in the aquifer of the study area. Meanwhile, the aquifer layer is found easily at a depth of 1 meter up to 30 meters.

Resistivity structural imaging of the Olkaria Domes geothermal field in Kenya using 2D and 3D MT Data inversion

The 2D and 3D MT inversion from 290 soundings were analyzed to visualize the nature and extent of structural control of the Olkaria geothermal reservoir system within and outside the ring structure. The ring structure bounds the drilled geothermal field under exploitation to the east and south of Olkaria Domes. The nature of subsurface structures was classified using dimensionality analysis. The resistivity models revealed three layers varying with depth. The upper conductive layer immediately below the surface as the reservoir seal, underlain by a resistive reservoir zone at about 2.5−4km, and the deeper conductive zone at a depth of about 5.5−8km interpreted as the heat source. The resistivity structure forming a channel to the near surface, is interpreted as the hydrothermal fluid's fault pathway. The study also shows the structures resembling sill formations mapped outside the geothermal system in the Domes field, while the dykes predominate in the reservoir.

Land Subsidence Investigation in Negeri Sila, Nusalaut Island, Using Resistivity Method

DOI:10.17014/ijog.9.2.The phenomenon of land subsidence in Negeri Sila of Nusalaut Island was caused by an earthquake in Ambon Island and surrounding areas on September 26, 2019 with the magnitude of 6.5. This research had been conducted using a resistivity method with a dipole-dipole configuration. Land subsidence occurred due to seawater intrusion around the area. The earthquake around Ambon Island was the trigger, so soil creep occurred.The purpose of this study is to obtain a weak resistivity zone area that indicates subsidence. The results showed a low resistivity value of 1-10 Ohm meters which indicated a weak zone of potential subsidence of the ground surface, and the presence of sea water intrusion into the area.

Bedding parallel fractures in fine-grained sedimentary rocks: Recognition, formation mechanisms, and prediction using well log

Core, thin section, conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag. Bedding parallel fractures are common in fine grained sedimentary rocks which are characterized by layered structures. Core and thin section analysis reveal that fractures in Lucaogou Formation include tectonic inclined fracture, bedding parallel fracture, and abnormal high pressure fracture. Bedding parallel fractures are abundant, but only minor amounts of them remain open, and most of them are partly to fully sealed by carbonate minerals (calcite) and bitumen. Bedding parallel fractures result in a rapid decrease in resistivity, and they are recognized on image logs to extend along bedding planes and have discontinuous surfaces due to partly-fully filled resistive carbonate minerals as well as late stage dissolution. A comprehensive interpretation of distribution of bedding parallel fractures is performed with green line, red line, yellow line and blue line representing bedding planes, induced fractures, resistive fractures, and open (bedding and inclined) fractures, respectively. The strike of bedding parallel fractures is coinciding with bedding planes. Bedding parallel fractures are closely associated with the amounts of bedding planes, and high density of bedding planes favor the formation of bedding parallel fractures. Alternating dark and bright layers have the most abundant bedding parallel fractures on the image logs, and the bedding parallel fractures are always associated with low resistivity zones. The results above may help optimize sweet spots in fine grained sedimentary rocks, and improve future fracturing design and optimize well spacing.

Geothermal resources prospecting using magnetotelluric and magnetic methods at Al Ain AlSukhuna-Al Galala Albahariya area, Gulf of Suez, Egypt

Recently, several urban and service development projects were carried out at the “City of Al-Galala Mountain”, along the Egyptian Gulf of Suez, between Al Ain Al-Sukhuna and Al-Galala Al-Bahariya Plateau. This region is adjacent to the Gulf of Suez rift, which is an active geothermal area, as indicated by the geothermal surface manifestations, such as thermal hot springs. It is a zone between two tectonic plates, which is expected to have several geothermal reservoirs; consequently, it represents a potential area for geothermal prospecting. Aeromagnetic data interpretation was performed to define the deep and shallow structures in the study area and their distribution to select a suitable site and perform more detailed prospection. Consequently, two sites were chosen to conduct a detailed study, with land magnetic and (1D MT) to discover variations in conductivity (resistivity) and fix the depth of predicted geothermal reservoir as well as the distribution of deep and shallow faults which can facilitate geothermal solutions flow and injection to exploit the geothermal source energy. The obtained results showed that the study area is intensely faulted with major NW-SE trend and minor E-W trend. Meanwhile, the (MT) results show several conductive and resistive zones at different depths, which could be correlated with faulting zones, suitable to predict geothermal sources and aquifers.

Composite Geoelectrical Investigation to Delineate Groundwater Feasibility in Hard Rock Area of Raipur, Chhattisgarh, India

In hard rock terrains, groundwater movement, migration, and storage occur through subsurface fractures. To assess the fractures and associated water, the authors carried integrated geophysical investigation with Wenner, GRP, Schlumberger, and Pole-Dipole array in the Indian state. The resistivity survey was carried out using a CRM-500 resistivity meter. The analyzed results are also re-verified with the help of IPI2WIN software. Initially, lateral and surface variations of resistivity were plotted by using Wenner and gradient resistivity profiling array. Then the low resistivity points were investigated with Schlumberger and Pole-Dipole array. In interpretation, low resistive zones identified correspond to the possible fractured zones. The results allowed mapping of the weathering zone at depth 12 to 15 m, and deep fracture lies below depth 55.0 m depth. The present study validates that the integrated geophysical survey is a powerful exploration technique to scrutinize and identify water-bearing fractures in the hard rock area.

Detection of soil pipe network by geophysical approach: Electromagnetic induction (EMI) and electrical resistivity tomography (ERT)

AbstractStudying soil pipes is a methodological challenge that needs improvement in detection methods in order to better recognize the role of piping erosion in land degradation and hillslope hydrology. This study explores electromagnetic induction (EMI) and electrical resistivity tomography (ERT) in order to identify soil pipes. The study was conducted in a mountainous area (the Bieszczady Mountains, SE Poland) under a temperate climate, where pipes develop in silty‐clayey soils. In the plot area, eight profiles were measured by the conductivity meter at different depths and then interpolated to present apparent electrical conductivity (ECa). Also, six ERT profiles were carried out using the Wenner‐Schlumberger electrode configuration. The ECa values measured by EMI are not very diversified, suggesting its lower sensitivity to changes in the ECa, whereas the ECa values measured by ERT are characterized by greater fluctuation, that is, better detection possibilities. ERT has revealed soil pipes as zones of higher electrical resistivity (ER >268 Ωm) than their surroundings (characterized below pipes by ER <105 Ωm) underlying the air filling of pipes (ER >427 Ωm), whereas EMI has revealed its higher sensitivity to water content. The EMI results have shown the lowering of the water table in the lower part of the slope, perhaps because of the drainage by a complex pipe network. EMI allows quick measurements of ECa providing information on water content, and thus indirectly soil pipes, but, it cannot delineate individual pipes. Only the integration of geophysical methods supported by field recognition provides an effective method to detect soil pipes.

Electrical Properties and Anisotropy of Schists and Fault Rocks from New Zealand’s Southern Alps under Confining Pressure

Magnetotelluric models spanning the Pacific–Australian Plate boundary in New Zealand’s South Island indicate a localized zone of low electrical resistivity that is spatially coincident with the ductile mid-crustal part of the Alpine Fault Zone (AFZ). We explored the source of this anomaly by measuring the electrical properties of samples collected from surface outcrops approaching the AFZ that have accommodated a gradient of systematic strain and deformation conditions. We investigated the effects of tectonite fabric, fluid saturated pore/fracture networks and surface conductivity on the bulk electrical response and the anisotropy of resistivity measured under increasing confining pressures up to 200 MPa. We find that porosity and resistivity increase while porosity and the change in anisotropy of resistivity with confining pressure (δ (ρ‖/ρ⊥)/δ (peff)) decreases approaching the AFZ, indicating the electrical response is controlled by pore fluid conductivity and modified during progressive metamorphism. Conversely, Alpine mylonites exhibit relatively low resistivities at low porosities, and lower δ (ρ‖/ρ⊥)/δ (peff) than the schists. These findings indicate a transition in both the porosity distribution and electrical charge transport processes in rocks that have experienced progressive grain size reduction and mixing of phases during development of mylonitic fabrics due to creep shear strain within the AFZ.

A magnetotelluric study of 3D electrical resistivity structure underneath the southern segment of the Red River fault zone, South China

• Imaged 3D resistivity structure beneath the southern Red River (RRF) and Xiaojiang Faults (XJF). • The southern RRF was shown electrically resistive and proposed mechanically strong. • The XJF shows a subvertical fault conductor zone under its eastern branch fault. • The southern RRF may have no large earthquakes in the future based on our results. The Red River Fault (RRF) is a continental-scale strike-slip fault forming the southwestern boundary of the Chuan-Dian block in the southeastern Tibetan Plateau. The kinematics and seismicity along the RRF are under debate over the years. Here, based on broadband magnetotelluric array data, we present a fine 3D electrical resistivity model in the southern segment of the RRF and its adjacent Xiaojiang fault zone (XJFZ). Our MT model shows a prominent electrical resistor extending to a depth of ∼20 km beneath the RRF and Ailao Shan shear zone. The southern RRF is imaged as a resistive fault zone, indicating no crustal fluids within this fault. The XJFZ represents a sub-vertical fault conductor zone bounded by bilateral crustal resistive blocks but a sharp contrast of resistivity across its western branch. The fault conductor zone along the eastern branch of the XJFZ ends at the resistive RRF, indicating the XJFZ may not develop beyond the RRF southward. Our MT model indicates that the resistive southern RRF is possibly not capable of occurring large seismicity in the future, but the southern end of the XJFZ is with seismic risk potential.

Archaeo-Geophysical Investigation of Ife City Grand Resort Iron Smelting Site at Ile-Ife, Southwest Nigeria

Abstract Ile-Ife in southwestern Nigeria is rich in art and craft traditions, most especially iron smelting. The town hosts hundreds of smelting sites with little or no archaeological record. Archaeo-geophysical prospection of a suspected smelting site in Ile-Ife involved the magnetic and electrical resistivity geophysical methods and archaeological excavation with the aim to identify its buried artefacts/features and date the site. The geophysical investigations located a circular/oval-shaped dipolar magnetic anomaly that coincided with a high resistivity zone, typical of a heat-impacted furnace or a slag trench. Iron slag, tuyere, fired clay furnace fragments, and charcoal were recovered from the pits excavated at the locations of the geophysical anomalies. Smelting activity at the site, from dated charcoal, took place at some point between the 13th-15th centuries AD, a middle to late age in Africa’s history of iron smelting. This study, therefore, validated the examined site as an ancient iron smelting site and situated its place in the archaeological history of iron smelting.

Monitoring CO2 storage using well-casing source electromagnetics

Successful geologic storage of CO2, whether in a carbon capture, utilization, and storage process or as part of enhanced oil recovery (EOR) operations, requires careful monitoring of the concentration of CO2 within the reservoir. Because injected CO2 is more electrically resistive than the in-situ brines and pore fluids in most storage sites, electromagnetic (EM) methods are well suited to map the distribution of injected CO2 over time. In particular, utilizing existing metallic well casings as electrodes to channel current to formation depth and measuring the resulting electrical and magnetic fields at the surface is an effective technique to image the deep and thin reservoirs of interest. This paper describes the theory behind the well-casing source EM method and discusses a series of field surveys carried out over a three-year period using the method to measure CO2 concentration at an EOR site in West Hastings, Texas. The surveys identify resistive zones that agree with the injection locations and geologic structure of the reservoir and show an increase in reservoir resistivity related to CO2 concentration between the initial field status and the middle survey. However, they also show an unexpected decrease in the resistivity within the reservoir between the last two surveys, which may be due to changes in survey parameters or CO2 injection patterns during that interval.

Implementing Electrical Resistivity Tomography to Delineate Soil Contamination Zone, Southern Baqubah City, Iraq

An electrical resistivity tomography survey was carried out in Diyala University campus, southern Baqubaa city, Iraq. The main aim of this study is to evaluate the efficiency of electrical resistivity tomography to detect the buried sewage system as well as to assess its environmental impact on the surrounding soil. Six parallel resistivity profiles were carried out at a perpendicular direction to the axis of the sewage system. Two-and three-dimensional geoelectrical models were constructed to determine the distribution of resistivity and its relation with both buried structures and contaminated zones. The results showed an intermediate relative resistivity zone (6-10 Ω.m) and several rounded very low resistivity zones (< 1 Ω.m), identifying the underground sewage system and contaminated soil, respectively. Based on variations in resistivity values, six holes (h1, h2, h3, h4, h5, and h6) were drilled. A total of six soil samples at 1.5m depth (1 sample per hole) were collected for heavy metals concentrations analysis. The results of the chemical analysis showed a higher concentration of heavy metals near the septic system than that the area away from it. Much lower resistivity zones (<1 Ω.m) and the higher concentration of heavy metals observed near septic system indicate the impact of contamination by migration from the septic tank into the nearby soil. The results of this study confirm the efficiency of electrical resistivity tomography for detecting a buried object and mapping contaminated zone for engineering and environmental applications.

New magnetotelluric data in the suture zone of Fennoscandia and Sarmatia

Presents the results of magnetotelluric soundings acquired in 2020 along the profile Rzhev– Velikie Luki, in the suture zone of three parts of Precambrian crust of East European platform: Fennoscandia, Sarmatia and Volga–Ural. In the central part of the profile, anomaly zone of increased conductivity in the crust was revealed. The crust conductor is weakly expressed on the components of the telluric tensor due to the screening effect of the conductive sedimentary cover; therefore, the focus in the qualitative analysis of data and inversion was made on magnetovariational parameters.According to the results of two–dimensional inversion carried out in the program of A.E. Kaminsky ZONDMT2D, on the geoelectric model a subvertical zone of low resistivity in the crust is identified, which is probably associated with the paleosubduction zone of the Belarusian Ocean Plate.

Bitumen as the cause of the occurrence of zones of low electrical resistivity in the basement rocks of the West Siberian plate

This article presents the results of studies of the material constitution and physical properties of rocks of foundation of the West Siberian Plate. It is shown that anthraxolite and kerite groups are present in bitumen rocks. We assume that the bitumens create a Late Paleozoic paleo-deposit, transformed under the conditions of apocatagenesis. Impregnation with highly transformed organic matter leads to a significant decrease in electrical resistivity to values of 1–30 Ohm metre, which must be taken into consideration when interpreting low-resistivity zones on log data.

3D Interpretation of a Broadband Magnetotelluric Data Set Collected in the South of the Chinese Zhongshan Station at Prydz Bay, East Antarctica

Antarctica is covered by a thick ice sheet, and the application of geophysical methods is necessary to image the subglacial structures for studying the hydrologic systems and tectonic deformations in the Antarctic continent. The magnetotelluric (MT) method is one of the best approaches to obtain the subglacial electrical resistivities. However, only a very small volume of data has been collected so far in Antarctica using this method. In this paper, we report on a broadband MT profile collected at 10 sites in the south of the Chinese Zhongshan Station at Prydz Bay, and a 3D resistivity model was constructed by inversion of these data. This 3D model shows two low resistivity zones at a depth shallower than 6 km. They are consistent with the low-velocity zones in the previous shear-wave model and can be interpreted as the result of interconnected fluids associated with a downward migration of subglacial water. In addition, a distinct eastward dipping low resistivity zoneis present in the crust, which extends from the top surface to the lower crust. Since its location coincides with the highly positive magnetization named Amery Lineament, it is proposed that this eastward dipping low resistivity zoneextending in the entire crust probably reveals the geometry structure of the Amery Lineament at depth. Besides, it can be inferred from this new 3D resistivity model that the Amery Lineament is at least a crustal-scale structure, which probably outcrops on the land surface but was covered by the ice sheets in the study area.

Electrical Imaging of a Shallow Free-Phase Stray Gas Plume from an Abandoned Exploration Well

Geophysical imaging of free-phase gas (FPG) within aquifers is an emerging method for understanding the mechanisms controlling stray gas migration from oil and gas wells. Crystal Geyser is an unsealed and partially cased well that transports stray CO2 gas to the shallow subsurface. Accumulations of subsurface CO2 FPG near Crystal Geyser have been inferred, but the actual location and dimensions remained unclear. Here, the subsurface FPG distribution surrounding Crystal Geyser was characterized by interpreting 2D electrical resistivity images with previous drilling records and field mapping. An approximately 70-metre-wide FPG plume was located laterally between Crystal Geyser’s conduit and the Little Grand Wash Fault. The FPG plume spanned the vertical extent of approximately 20 to 55 metres below the ground surface, located within the Slick Rock Member sandstone with the relatively low permeability Earthy Member silty sandstone acting as a caprock. The FPG plume was identified from an anomalously high resistivity zone within the Slick Rock Member that was not caused by lateral lithofacies changes or fault displacement. The conceptual FPG migration pathways beneath Crystal Geyser are presented, based on the interpreted FPG distribution from the electrical resistivity images combined with previous site characterization and the principles of buoyant FPG migration. FPG accumulates within the Slick Rock Member by buoyant up-dip migration beneath siltstone capillary barriers of the Earthy Member. FPG leaks to the ground surface within high permeability preferential pathways along the Little Grand Wash Fault and the conduit of Crystal Geyser.

A scalar-geometric approach for the probable estimation of the reserve of some Pb-Zn deposits in Ameri, southeastern Nigeria

The Cretaceous sedimentary sequence of the Asu River Group in Ameri, southeastern Nigeria play host to lead-zinc ore deposits in irregular mineralized veins of non-uniform geometry. Two deposits (designated DEPOSIT A and DEPOSIT B) were economically assessed using an integrated approach. This was performed by employing a geometry-based classical scheme involving the mathematical relationship between the three cardinal variables of ore reserve estimation namely: surface area, thickness and density. Firstly, detailed and extensive geological mapping was carried out to establish the geological attribute of the mineral deposits. Since reserve estimation extends beyond exposed faces, spontaneous potential traverse, vertical electrical sounding and horizontal profiling, being orthogonal to the trend of the enclosing veins were used to characterize the existing sub-surface stratification and create forward models that revealed the concealed ore geometry (limiting depth, lateral extents and thickness variations). Subsequent to delineation, the depth to the top of the target ore lodes was obtained by implementing the Peter's half slope technique on self-potential curves. Thickness values of the ore bodies of interest were applied in three numerical classical integration techniques, i.e. Trapezoidal, Simpson's and Simpson's third-eight rule, for volume estimation. To overcome the non-uniqueness problem of DC resistivity data interpretation, the available drilling data was applied. Samples retrieved from each lode were subjected to mass and volume analysis using the CS200 electronic balance and water displacement technique, to determine the average density of each lode. Results from 2D subsurface resistivity sections showed the lead-zinc deposits as zones of low resistivity in a background of high resistivity. The 1D stratigraphic models reveal a mean thickness estimate of 11.85 m and 10.50 m for DEPOSITs' A and B, respectively. Sample densities correlate well with the average density of pure galena. Applying the scalar-geometric rule, a combined estimate of 10,778.95tonnes was obtained, representing a relatively economically viable quantity worthy of medium scale extraction.

Geoelectrical Survey for Evaluation of Groundwater Potential Within the Basaltic Terrain of Chikotra River Basin, Maharashtra (India)

Geoelectrical data was acquired using Wenner array over 23 sites with constant electrode separation of 70 m over Chikotra Basin, Dist. Kolhapur, Maharashtra (India). The spatial variation maps of resistivity at depths from 2 to 70 m were plotted using Inverse Distance Weighted (IDW) technique for interpolation in ArcGIS 10.5 to obtain a comprehensive subsurface hydrogeological representation of the study area. High resistivity (>140 Ωm) up to 20m depth, indicative of massive basalts is deciphered towards the NE part of the study area, while the NW sector reveal low resistive (up to 40 Ωm) feature at shallow depths due to fractured basalts, thus conducive for groundwater exploration. Alluvium deposits and columnar jointed basalts in the central part depicts as EW trending conductive (< 30 Ωm) feature suggesting prospective groundwater zone. Low resistivity (6-50 Ωm) from shallow to deeper depths (up to 70m), in the southern region can be identified as potential aquifer system. Longitudinal geoelectric cross-sections are generated over four profiles to identify the lateral and vertical variation in geology and groundwater potential zones. The western and central part of the northern profile (A-A') is highly resistive with resistivity of the order of 80-140 Ωm constituting compact basalts and thus devoid of water. Low resistive zone (30 Ωm) in the eastern part suggests groundwater at shallow depths. Low resistivity zones ranging from 10-50 Ωm is observed at different depth levels over the central profile (B-B') which can be tapped for groundwater exploitation. Several sites over profiles C-C' and the southern-most D-D' suggest promising aquifer zones. Because defining prospective groundwater zones in hard rock terrain is difficult, it’s crucial to look into a river basin’s hydrogeological arrangement early on in the planning process.

Existence of High Temperature Geothermal Resources in the Igneous Rock Regions of South China

Large areas of Yanshan period granites with high heat production values (3–10 μW/m3) and mantle plume around Hainan province co-exist in Igneous Rocks Regions of South China (IRRSC). Surface manifestations are mainly warm/hot springs with temperatures below 90 °C and no typical phenomenon of high temperature resources have been observed. The main objective of this paper is to discuss the existence of high temperature geothermal resources and their possible locations under this kind of geothermal and tectonic background by analysis of high temperature heat sources, borehole temperature measurement, and reservoir temperature estimation. Two possible partial melts of the magma chamber were detected as high temperature heat sources in the Southern Leizhou Peninsular and North Hainan Island at a depth of 8–15 km. Other low resistivity zones in the upper crust are more likely caused by fluid in the formations or faults but not high temperature heat sources. This was also verified by borehole temperature measurement in these two areas, with maximum formation temperatures of 211°C and 185°C found, respectively. Reservoir temperatures from fluid geothermometers show lower temperatures of between 110–160°C for typical geothermal fields over the IRRSC but not in the Southern Leizhou Peninsular and Northern Hainan Island. In all, high temperature geothermal resources may be found in the Southern Leizhou Peninsular and on Northern Hainan Island.

Three‐Dimensional Electrical Resistivity Characterization of Mountain Pass, California and Surrounding Region

AbstractThe Sulphide Queen carbonatite deposit at Mountain Pass in southeast California is a world class rare earth element (REE) resource. This study images electrical resistivity structure of the REE deposit and surrounding area to characterize resources under cover. An east‐west elongated grid (35 × 15 km) of 65 wideband magnetotelluric stations spanning from eastern Shadow Valley to eastern Ivanpah Valley were collected and modeled in three‐dimensions (3‐D). Gravity, aeromagnetic, and geologic data are used to inform interpretation of structures in the resistivity model, including the following observations. Shadow Valley is filled with conductive sediment that locally dips southward to a depth of 1 km. The Kingston Range‐Halloran Hills detachment fault dips westward at ∼15 degrees. The REE deposit is a moderate low resistivity zone dipping southwest to a possible depth of ∼1 km, and is bounded by the North and South faults and bisected by the Middle fault. Ivanpah Dry Lake is underlain by a north striking southward dipping sedimentary basin. Two possible zones of mineralization are observed in Ivanpah Valley, one along the western edge of Ivanpah Dry Lake and one on the western edge of valley along a new inferred fault. The brittle‐ductile transition is imaged at ∼10 km below mean sea level. No deep electrically conductive structures are imaged to be related to the REE deposit likely due to the complex geologic history of the Mojave terrane. Future studies should regional target Proterozoic rocks and search within for geophysical signatures similar to Mountain Pass.