Predicting aquifer characteristics to enhance hydrogeophysical model in fractured/karstified rocks of Dammam Formation at Bahr Al-Najaf Basin, Iraq

Abstract

Groundwater represents a major water source in Bahr Al-Najaf basin. So, the knowledge of the aquifer parameters is an essential goal to assess and manage groundwater resources. A comprehensive view of the fractured and karstified aquifers within Dammam Formation at Bahr Al-Najaf basin is very important, because the karstified environments are very complex. This study is an attempt to extract mathematically empirical relationships between the hydraulic parameters and the geoelectrical properties, to improve the construction of a hydrogeophysical model, instead of using the conventional procedures of pumping tests or drill new well which need great effort and high cost. The enhanced hydrogeophysical model shows that the main aquifer has a uniform lithology of carbonate rocks, good water saturation and belongs to M. Dammam member. The correlation between hydraulic conductivity (K) m/day and aquifer resistivity ( $${\rho _0}$$ ) Ωm gave a logical relationship in such kind of aquifer, which has correlation coefficient (R2) equals to 0.737. In addition, the correlation between transmissivity (T m2/day) and both of transverse resistance (Tr) Ωm2 and longitudinal conductance (SL) Ω−1 revealed the similarity in lithological characteristics of middle Dammam aquifer due to the approximately equal values of strong R2 = 0.862 and 0.868, respectively. This may be due to the nature of the studied area as a discharge zone, which has a good porosity ( $$\varphi$$ ) of 22% and a high water saturation (Sw) equals to 1 approximately. The extracted relationship of direct proportionality between T (m2/day) and SL (Ω−1) is an important one. Therefore, this relationship can be used directly to calculate T (m2/day) mathematically. In the present study, the relations between the hydraulic parameters and the geoelectrical properties are expressed as linear equations instead of nonlinear, because we believe that it is mathematically more acceptable and reliable for hard rock aquifers that the M. Dammam aquifer is confined with a fully saturated thickness. In addition, the comparison between R2 of the linear and nonlinear relation of T (m2/day) with Tr (Ωm2) and T (m2/day) with SL (Ω−1) appeared to have little divergence of R2 equal to 0.028 and 0.001, respectively.