Estimation of hydraulic parameters and porosity from geoelectrical properties for fractured rock aquifer in middle Dammam formation at Bahr al-Najaf Basin, Iraq

Abstract EN

This study tries to examine the correlation between the hydraulic and geoelectrical parameters in an appropriate way, to construct empirical relationship at sites in Bahr Al-Najaf basin in the middle part of Iraq.

It is a first attempt of estimating mathematically the effective porosity, hydraulic conductivity, and transmissivity of a confined and anisotropic aquifer of Middle Dammam formation.

This aquifer is distinguished with the presence of fractures and paleo karst features of Carbonate rocks.

Sixteen of (VES) Schlumberger array using a maximum current electrode separation of (1000) m are conducted near existed wells and boreholes (with pumping test data).

The field (VES) data is interpreted, and values of geoelectrical parameters as layer resistivity and thickness, in addition to Dar Zarrouk parameters are determined.

Correlating Dar Zarrouk parameters with hydraulic conductivity and transmissivity (derived from pumping test analyses) at nine positions nearby selected boreholes is made.

Then representing the results as several graphical relationships of nonlinear curves with polynomial equations of second order and show very good Reliability (R2 ).

Directly proportional relations between longitudinal conductance with both; the hydraulic conductivity of R2 = 0.893 and the transmissivity of R2 = 0.868 are more conformable for such aquifer of average resistivity (70) Ωm.

Mathematically estimated values of hydraulic conductivity, transmissivity and those estimated by pumping test analyses are compared by means of histogram figures.

The small error ratios (RMS %) as (5.53) and (6.32) between the average values respectively, verify the validity of this methodology to be applied in other sites of similar characteristics.

Average effective porosity (secondary type) and water saturation of Middle Dammam aquifer are geophysically computed by Archie's equation as (22%) and (0.9) respectively.

These results are close to the typical porosity of saturated carbonate rocks as (27%), and agree with the prevail knowledge that the studied area is a discharge zone for Al-Shbecha hydrogeological basin.