INQUIRY FOR SUITABLE LOCATIONS FOR A DRILLING REGIME AT AN UPSLOPE ROCKY KNOLL OF LAWU ESTATE, WESTERN BYPASS, MINNA, NIGERIA

Abstract

Background: A client requested that the study group help determine suitable locations for a drilling regime on his lot, located on an upslope rocky knoll in Lawu Estate, Minna, Nigeria. There is no luxury of conducting an unimpeded wide-area survey for this housing Estate, as it is built up almost entirely. Therefore, the constrained area to be surveyed necessitated the adoption of the "electrical drilling," or vertical electrical sounding, mode of the geoelectrical method to satisfy the client's inquiry. Aim: To carry out a purpose-specific survey to pinpoint the best location in a built-up property at the upmarket Lawu Estate that would be suitable for a drilling regime targeted for household consumption. The specific objectives are to determine the subsurface layer structure, to identify fracture zones with potential for water accumulation, and to estimate the depths of potential aquifers. Methods: The survey crew reconnoitered the study area to georeference locations for the VES survey within the 30 m x 20 m lot. Owing to the extensive build-up at this lot, only a four-point traverse along the 30-metric dimension of the building's frontage was demarcated in the northeasterly direction, thereby limiting the survey crew's desire to define an appropriate survey grid. The VES data acquisition followed the "traditional" sequence of Schlumberger array layout measurements, in which the current and potential probes are maintained at the same relative spacing and the whole spread is progressively expanded about a fixed central point. Results: Log-log and pseudosection plots were generated from the acquired data, from which the conventional three-layer structure is deciphered, with a desired 193 Qm for VES Station 4 at the third layer. Discussion: The acquired and processed data for this study were subjected to a suite of empirical rules-of-thumb procedures for interpreting VES data in the Nigerian Basement Complex geological province, with VES Station 4 showing the most encouraging 100% result. Conclusion: Drilling to a depth of 100 m at Station 4 is recommended based on the identified fractured basement at this depth.