Causes of Borehole Failure in Complex Basement Terrains: ABUAD Case Study, Southwestern Nigeria

Ogundana, A.K and Aladesanmi, A. O and Okunade, A and Olutomilola, O.O (2015) Causes of Borehole Failure in Complex Basement Terrains: ABUAD Case Study, Southwestern Nigeria. American Journal of Engineering Research (AJER), 4 (10). pp. 1-10. ISSN Online: 2320-0847 Print : 2320-0936

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Abstract

A preliminary assessment of primary causes of borehole failure has being conducted using Afe Babalola University as a case study. A total of fourteen boreholes (namely borehole 1-14) were studied, vertical electrical soundings, depth sounding, flushing and pump testing were conducted on each of the boreholes to establish their status at the time of the study and possible evaluation of the groundwater potential of the wells. Four out of the fourteen boreholes (borehole 1-4) are productive and in-use, while the remaining ten (borehole 5-14) are out-of-use and abandoned for various. The productive holes were able to support continuous flow of water for over 3 hours without drop in volume of water flow. Seven of the holes (boreholes 5, 6, 8, 9, 11, 12 & 14) failed and were abandoned because of low yield (could not flow beyond 5 minutes), while the remaining three (boreholes 7, 10 & 13) failed and were abandoned due to wrong location and improper completion, caving/formation problems, and wrong installation/completion respectively. Proper well completion is essential in areas prone to caving and other formation related problems. Air drilling should be avoided in areas with thick and loose overburden. Right mixture of drilling mud should be applied to secure the hole wall while flushing should be continuous throughout drilling in such formation. Casing should be done immediately and such holes should be lined and grouted. Timers should be installed on low yield wells and regulated/programmed for 5 or 10 minutes flow depending on the recharge rate. Pump rating for installation should be strictly based on well recharge rate. Productive wells should be properly maintained and monitored for optimal performance.

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