Geophysical borehole logging for control of driller’s records: hydrogeological case study from Voltaian sedimentary rocks in northern Ghana

Abstract

The low borehole yielding potential and the high drilling failure rate of the Voltaian sedimentary rocks of Northern Ghana have been of concern to many local hydrogeologists and international donors. Consequently, several donor-supported projects have been instituted within the last few years with the view to study the hydrogeological characteristics of this 'difficult' rock system. One such project is the geophysical borehole logging of 13 boreholes drilled into the Voltaian sedimentary rocks of Northern Ghana to enhance detailed hydrogeological assessment. Natural gamma detectors embedded in the five exploratory logging tools employed for the study ensured depth control by comparing their individual gamma log signatures. The combined gamma and formation resistivity/ conductivity response logs provided more detailed lithological information than were shown in the driller's/geologist's logs. Significant discrepancies between the logging results and the reported drilled depths, construction depths, and screen settings were observed in seven of the thirteen investigated boreholes. Thus, the reliability of driller's borehole records seems questionable, which will hamper hydrogeological studies and the mapping of groundwater resources. Further, it may be supposed that the productivity of most wells in Ghana is compromised by poor depth control of screen placement.

Hydrogeological Analysis of Cretaceous and Tertiary Aquifers in Semiarid Sokoto Basin, Northwestern Nigeria: Implications for Sustainable Groundwater Development

“…Regions having greater yields (more than 3060 Lpm) are limited. Comparison with other sedimentary basins in Africa showed that mean borehole yield in the Sokoto basin was greater than values obtained from the Voltaian sedimentary aquifers in Northern Ghana (0.3 to 72 5-1200 Lpm) [88]. In Ghana's alluvial province, the estimated borehole yield ranged from 1 to 15 m 3 /h [89].…”

Integrating gamma log and conventional electrical logs to improve identification of fracture zones in hard rocks for hydrofracturing: a case study from Ghana

“…in hard rocks (Telford et al 1990). These borehole logging tools offer one of the most reliable ways of detecting fractured sections intercepted by the borehole, since some of these fractures may be masked and detected as a single anomaly during a surface geophysical measurements (Agyekum 2009;Awini 2009;Ratnakar and Singh 2008;Krishnamurthy et al 2003;Lee et al 1991;Lee 1985). Gamma log is an important and standard nuclear radiation logging tool, which can be operated in both cased and opened boreholes filled with air, water or drilling fluid, giving them an advantage over electrical logging suites (Kearey et al 2002;Driscoll 1986).…”

“…It is generally used as one of the primary tool for lithological investigation (Keys 1997). For instance in Ghana, Agyekum et al (2013) deployed the natural gamma detectors embedded in the five exploratory logging tools to investigate significant discrepancies between the logging results and the driller's/geologist's logs results on reported drilled depths, construction depths, and screen settings of boreholes in the Voltaian sedimentary rocks.…”