Shallow Geothermal Resource Evaluation Using Borehole Temperature Logging and Gravity in Ihiala, Anambra State

The increasing global interest in shallow geothermal energy for heating and cooling applications has highlighted the need for baseline thermal resource characterization in Nigerian cities, including Ihiala in Anambra State. This study evaluates shallow geothermal resources in Ihiala using borehole temperature logging and gravity data interpretation. Temperature profiles were measured in eighteen existing water boreholes across the study area using a digital temperature logger at 1 m depth intervals, with borehole depths ranging from 25 m to 120 m. Ground gravity measurements were acquired at 200 m station spacing along four profiles crossing areas with contrasting geology, and Bouguer anomaly profiles were computed for structural interpretation. Geothermal gradients computed from the borehole temperature profiles range from 28 to 56 mK/m, with the highest gradients recorded in the southeast of the study area near a mapped intrusive body. Ground surface temperatures average 28.6 degrees Celsius, and subsurface temperatures at 100 m depth range from 31.4 to 34.2 degrees Celsius. Heat flow estimates derived from gradient and estimated thermal conductivity range from 48 to 92 mW/square metre. Gravity anomaly patterns correlate with the thermal gradient distribution, with gravity lows interpreted as felsic intrusions spatially coinciding with elevated geothermal gradients. The most favorable zone for ground source heat pump systems is identified in the southeast of Ihiala where thermal gradients and accessible borehole depth combine optimally. This study provides a baseline thermal resource map for shallow geothermal development planning in Ihiala.

Keywords: geothermal gradient, borehole temperature, gravity, heat flow, ground source heat pump