Use of 2D azimuthal resistivity imaging in delineation of the fracture characteristics in Dammam aquifer within and out
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ORIGINAL PAPER
Use of 2D azimuthal resistivity imaging in delineation of the fracture characteristics in Dammam aquifer within and out of Abu-Jir fault zone, central Iraq Ahmed Srdah Al-Zubedi 1 & Jassim M. Thabit 2
Received: 12 March 2015 / Accepted: 10 September 2015 / Published online: 9 December 2015 # Saudi Society for Geosciences 2015
Abstract The 2D azimuthal resistivity imaging is a new technique used to determine the subsurface fracture characteristics in Dammam aquifer within and out of Abu-Jir fault zone, southwest of Karbala City, central Iraq. This technique was carried out by Wenner–Schlumberger array through 11 stations distributed within and out of Abu-Jir fault zone. Each 2D azimuthal station includes four 2D imaging lines in different directions (N-S, E-W, NE-SW, and NW-SE) with coverage equals to 45°. The 2D imaging line consisted of 60 electrodes at 10-m spacing. The 2D azimuthal results showed two types of fracture zones. The first is formed from cavities that developed from small fractures and fissures through a dissolution process of carbonate rocks. In some cases, this zone is found as horizontal canal near the Earth’s surface. While the second fracture zone formed by tectonic movements and that typically occurs as vertical and nearly vertical zones of fractures. These zones are characterized by increasing of resistivity values within Abu-Jir fault zone and decreasing out of it. In general, the fracture density of these zones is increased with the depth in SE, E, and NE directions within and out of Abu-Jir fault zone. Keywords 2D azimuthal imaging technique . Fracture characteristics . Dammam aquifer * Ahmed Srdah Al-Zubedi [email protected] Jassim M. Thabit [email protected]
1
General Commission for Groundwater, Ministry of Water Resources, Baghdad, Iraq
2
Department of Geology, College of Science, Baghdad University, Baghdad, Iraq
Introduction Fractures are breaks in rocks caused by tectonic stresses. They are more common in carbonate rocks than in sandstones and typically occur in specific directions which are dictated by the regional tectonic stresses. The fractures may extend to the surface where they are observed and studied at outcrops. On the other hand, they may terminate in the subsurface or may be covered by overburden which makes them impossible to be studied and characterized at the ground surface. The unavailability or inaccessibility of good outcrops makes it imperative to develop methods and tools for studying the fractures in the subsurface. Geophysical methods such as the resistivity method are very useful in this regard. All resistivity techniques were used in delineation of the subsurface fracture characteristics, for example, Dutta et al. (1970). McDowell (1979). Al-Ane (1993). and Krishnamurthy et al. (2000) used 1D electrical resistivity techniques to detect the cavities and fracture zones. Busby (2000). Massoud et al. (2009). and Odoh (2010) applied 1D azimuthal resistivity technique to determine the characteristic fracture patterns. Al-Zoubi et al. (
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