Borehole failures in crystalline rocks of South-Western Nigeria

Boreholes drilled in the crystalline rocks of Nigeria have a reputation of failures and low yields. The performance of 256 boreholes drilled in different parts of the crystalline rocks of SW Nigeria were reviewed to determine their failure characteristics. 100% success was claimed for 105 boreholes constructed by one driller. Out of 111 other borehole records supplied by three other drillers 35 were abortive, representing a failure rate of 32%. In contrast, 24 owners of 40 boreholes reported 24 failures representing a failure rate of 60%.The common causes of borehole failure in the crystalline rocks of SW Nigeria are seasonal variations in water level, improper casing of the overburden, damage to pumps and other system failures such as blocked pipelines and malfunctioning tanks. Non-penetration into the water bearing horizon also features as a cause of borehole failure in this study.It is suggested that proper construction, operation and maintenance of boreholes will reduce the incidence of borehole failures in crystalline rocks of SW Nigeria.