Siting High-yielding Boreholes: In the Crystalline Basement in Burkina Faso: Contribution of Electrical Anisotropy Measurements

Geological studies, remote sensing and geophysical investigation around twenty two boreholes (highly and moderately productive, or dry ones) have clarified aquifers productivity factors of the crystalline basement of Burkina Faso as well as their geophysical signature. To boost the rate of successful siting of highly productive boreholes (rate greater than 5 m3 / h) from 15 to 56%, the square device enabling to perform anisotropy profile was tested. This system provided some very interesting results for research of high yielding drilling sites.

Thanks to electrical and electromagnetic geophysical methods after a geological and remote sensing study, ten sites with twenty-two yielding, mildly yielding or dry boreholes have been studied in details. Some number of productivity factors of crystalline rocks aquifers in Burkina Faso has been detected as the contribution of electromagnetic hydro geophysical prospecting. Migmatic granites characterize the geology of the sites. These rocks are very fractured with important pegmatic veins intrusions.

The yielding wets drilling are located on fractures longer than five kilometres.

Lateral extension of the discontinuity is less than fifty meters.

An important thickness of fractured rock is necessary, it characterize the "trailing rise" of electrical sounding curve.

There is a correlation between the yield of a borehole and the anisotropy ratio. A perpendicular anisotropic profile allows choosing a site for yielding boreholes.