Investigation of petrophysical and hydrogeological parameters of the transboundary Nubian aquifer by combining geophysical and hydrogeological methods: a case study of Khartoum state, Sudan

Abstract

Abstract This research follows an integrated approach for delineating subsurface lithology and estimating petrophysical and hydrogeological parameters of the Cretaceous Nubian formation aquifer in Khartoum state, Sudan. The Nubian aquifer is a fossilized transboundary regional aquifer that covers more than a quarter of the Sudan’s area. The integrated approach includes geophysical well-logging, surface geophysical electrical methods, and pumping data analysis. Geophysical well-logs, including self-potential (SP), natural gamma ray (GR), and long normal resistivity (RS) for with the aid of described lithological logs are employed to delineate the transboundary Nubian aquifer, and the obtained results are extrapolated by vertical electrical sounding (VES) and boreholes lithological logs. As a result, two aquifers are detected. An upper aquifer of an average thickness of 50 m and a lower aquifer of more than 200 m. These two aquifers are hydraulically connected under semi-confined to confined conditions. Consequently, areal variation maps of depth to aquifers and resistivity are prepared to avoid wells constructions failures. For a thorough evaluation of the aquifers, in the first stage, the petrophysical and hydrogeological parameters, including formation factor, total and effective porosity, shale volume, and hydraulic conductivity, are measured solely from geophysical well-logs with the aid of hydrochemical data. In the second step, the results of geophysical well-logs are interpolated and generalized to detect the spatial variation of the measured petrophysical and hydrogeological parameters over the study area. This was achieved by combining VES measurements and pumping test data with the geophysical well logs. The applied scheme minimized the expenses and effort of the global hydrogeological survey by improving the spatial coverage of the detected parameters. The measured petrophysical and hydrogeological parameters revealed that this formation is highly productive and ideal for groundwater development. However, optimizing groundwater discharge rates is recommended for sustainable water supply in Khartoum state.