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, we carried integrated geophysical investigation with Wenner, (GRP), Schlumberger, and Pole-Dipole array in Indian State. The resistivity survey 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.

Seismic Wave Simulation in Fractured Media

Fractured reservoirs, including unconventional fields, are important in global energy supply, particularly for carbonate source rocks. Fractures can influence subsurface fluid flow and the stress state of a reservoir. The knowledge about the existence of fractures, their spatial distributions, and orientations can help us optimize well productivity and reservoir performance. Seismic detection of subsurface fractures provides important measurements to remotely image field-scale fractures. In developing such technology, forward modeling of the seismic response from fractures in the reservoir provides an important alternate tool for imaging subsurface fractures. In this paper, we implement a seismic modeling algorithm which can simulate 3D wave propagation in an arbitrary background media with imbedded fractures. During modeling, the fractures are added to the background medium by linear slip theory. Examples demonstrated the impacts of fractures on the wave propagation patterns for both PP and PS waves. We also investigate the amplitude versus offset (AVO) effects caused by fractures in a layer media and lay out potential applications of forward modeling in the inversion of fracture parameters and the estimation of fluid contents.

The Application of Geophysical Methods in Identification of Subsurface Fractures in The Vicinity of a Poor Performance Percolation Tank

Percolation tanks are constructed to conserve the rainwater in large quantities and allow more infiltration in its area of influence. Sometimes due to heavy fracture concentration/thick weathered zone, the water in percolation tank migrates fast in short period and tank becomes dry, which leads to early scarcity conditions. The village karkatta of taluka and district Latur is one such village, where water is provided by constructing two wells in the vicinity of percolation tank. The water level in the percolation tank depletes fast and the tank becomes dry in early summer. Also one cement nala bandhara was constructed in the downstream of the nala. The village is funded by UNICEF to implement MUS (Multiple Water Users) project. The area is surveyed by applying both electrical resistivity methods and low frequency electromagnetic methods in submergence of tank as well as in the downstream of percolation tank. The studies reveal that the leakages are due to thick vesicular basalt followed by fractured massive basalt. Suitable remedial measures are recommended to slow down the subsurface flow so as to improve the performance of the percolation tank.

Geotechnical Properties Evaluation Utilizing Geological, Geomorphological and Shallow Geophysical Surveys of Wadi Habib Entrance Site, Eastern Desert, Egypt.

An integrated approach is carried out in a proposed engineering site at Wadi Habib, Egypt. The study aimed to characterize the geological, geotechnical and hydrogeological environment evaluate their suitability for civil engineering constructions. The present study reveals that the area is mainly covered by the Eocene carbonate rocks uncomfortably overlain, in some areas, by the Oligocene gravels. The Pliocene mudstone and the Pleistocene/recent fine clastic deposits are recorded in the subdued ground. The surface and subsurface fractures around Wadi Habib area are mainly represented by high angle normal faults trending NNW- SSE, NW-SE, WNW-ESE and ENE-WSW. The morphometric analysis reveals that Wadi Habib is generally of seventh order, sinuous course, elongated, untainous and hilly, course topographic texture and high resistance and low permeable floor. A total of 32 seismic refraction profiles were conducted in two directions N 35° W and N 55° E. Three geoseismic layers of different lithological, compressional and shear velocities and elastic properties are achieved. The geotechnical parameters involving kinetic elastic moduli, soil material competence parameters and the bearing capacity are estimated and hence indicated the characteristics of the foundation materials for civil engineering constructions in the investigated site. Also, 30 VES’es are implemented and interpreted to test the geological and hydrogeological conditions. Subsurface geoelectrical layers are delineated and verified. The proposed site is characterized by a relatively low to moderate seismicity. The geotechnical parameters of geoseismic layers and the hydrogeological probable troublesome (cavities, fractures, faults) for building structure and soil suitability for foundation purposes are concluded

Effectiveness of 2D Induced Polarisation & Electrical Resistivity Tomography in Mapping Fracture Heterogeneity in Foundation Soils.

Inhomogeneity caused by fractures can constitute real problems in foundation soils which consequently can lead to structural failure. 2D Electrical Resistivity Tomography (ERT) has been exceedingly popular in mapping near surface discontinuities that can possibly affect engineering structures. The effectiveness of using Induced Polarisation Tomography (IPT) in mapping subsurface fractures was explored. Using the same field way out for both ERT and IPT, investigations were carried out at a failed structure with foundational inhomogeneity in the Nsukka area, Southeastern Nigeria. Four Electrical Resistivity Tomography (ERT) and four Induced Polarisation Tomography (IPT) were carried out. Electrical Resistivity Tomography for profile line one (ERT1) and that of the opposite section, ERT3, revealed a fault trending NNW- SSE. This anomaly was also observed on the Induced Polarization Tomography for profile line one (IPT1) as well as that of profile line three (IPT3) at the same offset distances, delineating the same fracture zone. A second fault trending in NE-SW was mapped by the Electrical Resistivity Tomography for profile line two (ERT2) and Electrical Resistivity Tomography for profile line four (ERT4). The fault was also visible in the Induced Polarization counterparts, IPT2 and IPT4. Field validation along mapped trends recorded subtle cracks on the foundation along the same trend detected by the IPT as well as the ERT.

Electrically Inferred Subsurface Fractures in the Crystalline Hard Rocks of an Experimental Hydrogeological Park, Southern India

We investigated a network of fractures forming the flow paths within the crystalline granitic rocks of an experimental hydrogeological park (EHP) with the help of electrical resistivity surveys. The experimental study located at managed aquifer recharge (MAR) site of EHP has measured a distinct variation in the apparent resistivity for deeper electrical signals that localize the presence of interconnected water-saturated fractures. Usually, profiles close to the MAR tank depict low apparent resistivity values from deep signals across in-situ fractures and resistivity amplitude increases away from the tank. We modeled and simulated the presence of water-saturated fractures by a simple three-layered model having embedded shallow heterogeneities in the saprolite layer, vertically interconnected multiple thin conductive horizontal layers in the fissured zone, and an underlain un-weathered crystalline granitic basement. These fractures produce a distinct variation in the resistivity both for modeling and inversion exercises. The decadal time-lapse electrical resistivity surveys, after the establishment of the MAR tank, mark similar repetitive main features with a distinct drop in resistivity depicting the presence of water-saturated fractures. An overview of 3D resistivity model characterizes the subsurface heterogeneities, presence of possible flow paths for shallow depths <30 m, and indicative of possible flows in the interconnected deep fractures for depths >30m.

Power Density Distribution in Subsurface Fractures Due to an Energized Steel Well-casing Source

Robust in situ power harvesting underlies the realization of embedded wireless sensors for monitoring the physicochemical state of subsurface engineered structures and environments. The use of electromagnetic (EM) contrast agents in hydraulically fractured reservoirs, in coordination with completion design of wells, offers a way to transmit energy to remotely charge distributed sensors and interrogate fracture width, extent, and fracture-stage cross-communication. The quantification of available power in fracture networks due to energized steel-cased wells is crucial for such sensor designs; however, this has not been clarified via numerical modeling in the limit of Direct Current (DC). This paper presents a numerical modeling study to determine the EM characteristics of a subsurface system that is based on a highly instrumented field observatory. We use those realistic field scenarios incorporating geometry and material properties of contrast agents, the wellbore, and the surrounding geologic environment to estimate volumetric power density near the wellbore and within hydraulic fractures. The numerical modeling results indicate that the highest power densities are mainly focused around the wellbore excited by a point current source and the fracture boundary. Using DC excitation, the highest power density in the fracture is at the fracture tip. The relatively high-power density on the order of tens of mW/m 3 at the vicinity of the wellbore and at fracture tips suggests that remote charging of sensor devices may be readily possible. Simulation results also show that the region of the highest power density can be significantly increased when the EM source is located inside a conductive fracture, which may lead to a promising deployment strategy for embedded micro-sensors in geologic formations.