Resistivity Method Contribution in Determining of Fault Zone and Hydro‑Geophysical Characteristics of Carbonate Aquifer, Eastern Desert, Egypt
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Applied Water Science (2018) 8:1 https://doi.org/10.1007/s13201-017-0639-9 ORIGINAL ARTICLE Resistivity method contribution in determining of fault zone and hydro‑geophysical characteristics of carbonate aquifer, eastern desert, Egypt A. I. Ammar1 · K. A. Kamal1 Received: 6 July 2014 / Accepted: 31 August 2017 © The Author(s) 2018. This article is an open access publication Abstract Determination of fault zone and hydro-geophysical characteristics of the fractured aquifers are complicated, because their fractures are controlled by diferent factors. Therefore, 60 VESs were carried out as well as 17 productive wells for determin- ing the locations of the fault zones and the characteristics of the carbonate aquifer at the eastern desert, Egypt. The general curve type of the recorded rock units was QKH. These curves were used in delineating the zones of faults according to the application of the new assumptions. The main aquifer was included at end of the K-curve type and front of the H-curve type. The subsurface layers classifed into seven diferent geoelectric layers. The fractured shaly limestone and fractured limestone layers were the main aquifer and their resistivity changed from low to medium (11–93 Ω m). The hydro-geophysical properties of this aquifer such as the areas of very high, high, and intermediate fracture densities of high groundwater accumulations, salinity, shale content, porosity distribution, and recharging and fowing of groundwater were determined. The statistical analysis appeared that depending of aquifer resistivity on the water salinities (T.D.S.) and water resistivities add to the fracture + − 2+ 2+ 2− density and shale content. The T.D.S. increasing were controlled by Na , Cl , Ca , Mg , and then (SO4) , respectively. The porosity was calculated and its average value was 19%. The hydrochemical analysis of groundwater appeared that its type was brackish and the arrangements of cation concentrations were Na+ > Ca2+ > Mg2+ > K+ and anion concentrations − 2− − − were Cl > (SO4) > HCO3 > CO3 . The groundwater was characterized by sodium–bicarbonate and sodium–sulfate genetic water types and meteoric in origin. Hence, it can use the DC-resistivity method in delineating the fault zone and determining the hydro-geophysical characteristics of the fractured aquifer with taking into account the quality of measure- ments and interpretation. Keywords DC-resistivity method · VESs · Fault zones · Hydro-geophysical characteristics · Statistical analysis · Hydrochemical analysis · Carbonate aquifer Introduction consequently confning the fow to fractured zones of aquifer and thus making the situation alarming. Cemen et al. (2008) In general, groundwater is the major source to supply the and Halihan (2008) reported that the fractures in aquifer water needed for industrial, agricultural, and domestic pur- rocks afect the fow of water, and therefore, numerical poses and hence largely contribute to the economic devel- modeling of the fuid fow requires an understanding of the opment of such regions, especially for those exposed to geometry and density of fractures that have a great infu- arid and semi-arid climatic conditions, where the surface ence on the discharge and recharge mechanisms. The lack of water resource is limited. The increasing stress on ground- characterization data generally comes from the cost involved water exploitation in such areas causes decline in its level in drilling, completing, maintaining, and sampling wells. This cost is higher in fracture and karstic aquifers due to the higher drilling costs and the heterogeneous fow felds * A. I. Ammar typically require more data than are available from discrete [email protected] sampling techniques which provide only limited two- or 1 Research Institute for Groundwater, National Water Research three-dimensional data. Most of methods of characterizing Center, Cairo, Egypt these aquifers have relied on two detection and monitoring Vol.:(0123456789)1 3 1 Page 2 of 27 Applied Water Science (2018) 8:1 strategies. The frst strategy involves discrete point sampling geological, and hydrogeological properties of the carbonate of fuids using wells, springs, or multilevel piezometers for aquifer. These data assisted in how to delineate the faults, integration and interpretation. The second strategy uses indi- fracture zone distribution, distribution of shale horizontally rect measurements through surface or bore-hole geophysical and vertically, groundwater quality, the role of faults in con- techniques. Therefore, at this study for understanding this nection between multiple aquifers, and the expected source complex fractured aquifer and for giving the facilities for of groundwater. According to geoelectrical and hydrochemi- studying and for solution the complex determinations of the cal, geological, and hydrogeological properties of this aqui- diferent hydrogeological parameters of this aquifer, we used fer, it is assumed that the fractures density and intensity of the surface resistivity method which depended on the imped- the carbonate aquifer distributed horizontally and vertically ance of the electrical current during penetration through the and may control by structure tectonics such as faults. These subsurface conductive and non-conductive rocks, to provide features may important in feeding this aquifer and control- more complete site data coverage, with the available hydro- ling in its groundwater quality adds to determine the loca- geological data. In general, fow features (such as faults that tions of low and high groundwater accumulation. Therefore, conduct fuids) and higher porosity lithologies are indicated geophysical methods are occasionally used to characterize by low-resistivity anomalies. In addition, the hydraulic karstic features (caves, sinkholes, faults, and fractures) prior parameters of the formation may be estimated using elec- to any hydrogeological or geological studies. trical methods (Purvance and Andricevic 2000a, b). The In general, the electric conduction in most rocks is essen- electrical data produced from this type of study may help tially electrolytic. This is because most mineral grains, characterize heterogeneity, fractures, and aquifer parameters except metallic ores and clay minerals, are insulators, elec- (Herwanger et al. 2004; Niwas and de Lima 2003). Carbon- tric conduction being through intertitail water in pores and ate aquifers are complex in nature and are subjected to high fssures or fractures. Groundwater flling the pore space of variability of the hydrogeological parameters depending on a rock is a natural electrolyte with a considerable amount the fractures distribution and interconnect between them. of ions present to add to conductivity. As a rule, the more The carbonate aquifers are normally traversed by lineaments porous or fssured/fractured a rock and the larger its ground- such as fault and fracture zone distributions that make the water content, the higher is the conductivity and the lower is groundwater dynamics more complex, and hence, their char- the resistivity. If clay minerals are present in a water-bearing acteristics become more important to understand the frac- rock, a relatively large number of ions may be released from tured aquifer setup. These fault and fracture zones play an such minerals by ion-exchange processes, the ions contrib- important role in the groundwater dynamics and it act as uted by these processes add to the normal ion concentration indicator to locate the groundwater resources and also the in pore water, and the net result being an increasing con- expected feeding of the aquifer either from the deep aquifer, ductivity. All rocks containing clay minerals (in wet state) from the neighborhood aquifer, or from streams. In general, exhibit abnormally high conductivity in this account. Hard the waids or drainage patterns over the hard rocks are con- rocks are bad conductors of electricity, but many geological trolled by the subsurface structure-like faults. These drain- processes can alter a rock and signifcantly lower its resistiv- ages are interesting in feeding the subsurface aquifer and ity. For instance, dissolution, faulting, shearing, columnar the water into the fractures will be mixed water if the faults jointing, weathering, and hydrothermal alteration usually assisted in connecting with the deep aquifer. Therefore, these increase the rock porosity and fuid permeability, and hence features are very important in expecting the potentialities lower resistivity. At this study, it is believed that the dissolu- of the subsurface aquifer with focusing on the horizontal tion in the form of small caves or vugs and faulting in form and vertical conductive fracture zone distributions and the of fractures, fssures, and joints. These processes are more down-throw or up-throw of the recorded faults and may be abundant in the areas of low resistivities values which refect the potentialities increased far away from the faults, or fault the very high-to-high fractures. In contrast to the above pro- should be avoided or there is really nothing linear available cesses, precipitation of calcium carbonate (CaCO3) or silica in area, where it is needed. Hence, there is need of detailed reduces porosity and hence increases resistivity. These pro- characterization of lineaments and its validation for the cesses are more appearance in the areas of high-resistivity groundwater potentiality and feeding. values which refect the presence of intermediate fractures Chandra et al. (2006)