A Short Review on The Application of Potential Field Methods for Geothermal Energy Exploration

Theophilus Aanuoluwa Adagunodo, Covenant University, Ota, Ogun State, Nigeria
Ayobami Ismaila Ojoawo, University of Ibadan, Ibadan, Oyo State, Nigeria
Julius Oluwasegun Omidiora, Covenant University, Ota, Ogun State, Nigeria
Rebecca Aderonke Ogundiya, Precious Cornerstone University, Ibadan, Oyo State, Nigeria
Corresponding author: theophilus.adagunodo@covenantuniversity.edu.ng

Geothermal energy exploration has a long history in Nigeria.
Geothermal resources exist uniformly beneath the subsurface, varying in concentration by geological region.
Potential field methods (magnetic and gravity techniques) are reviewed for geothermal exploration.
Processed potential field data can reveal subsurface structures after applying filtering techniques (for magnetic) or corrections (for gravity).
Proper exploitation of geothermal energy can contribute to clean energy generation for domestic and industrial use.

1. Introduction

Due to increasing pollution and dwindling economic resources, there is a need for sustainable energy sources in Nigeria.
Nigeria primarily relies on hydro, wind, oil, and gas for energy.
Crude oil exploitation is insufficient to meet rising energy demands.
Geothermal energy (from hot water springs) is viable for power generation and other heating purposes.
Rising fuel prices have created interest in geothermal energy as a natural resource.
Previous research indicates a lack of practical geothermal projects in Nigeria.
Geothermal energy comprises energy from the Earth's crust (20%) and from radioactive decay (80%).
Geothermal gradients reflect the temperature difference from the Earth's core to the surface, influencing thermal energy conduction.
The Curie depth is where magnetic minerals lose ferromagnetic properties due to temperature increases.

Geothermal energy resources are present in Nigeria's subsurface, with varying concentrations by geological domain.
Regions with notable geothermal potential include northern Nigeria (e.g., Cretaceous Benue Trough) showing higher prospects than the south due to overpressured sediments aiding heat flow.
Research indicates substantial geothermal gradients and heat flows across various basins:
- Nupe Basin: Gradients 10-450 °C/km, heat flow 30-120 mW/m².
- Ikogosi Warm Spring: Curie point depth 15.1 km, heat flow 91.2 mW/m².
- Osogbo-Ogbomoso Axis: Gradients 75 °C/km, heat flow 190 mW/m², and minimal Curie depth 5.5 km.
- Sokoto Basin: Gradients 20.84-52.11 °C/km, heat flow 52.11-130.28 mW/m².

Nigeria's geological structure consists of basement rocks and sedimentary basins with varying historical deposition.
Basement rocks include crystalline and metamorphic rocks; sedimentary rocks are primarily Cretaceous and Tertiary (sandstones, gravels).
Major sedimentary basins include Anambra Basin, Benue Trough, Bida-Nupe Basin, Chad Basin, Dahomey Basin, Niger Delta Basin, and Sokoto Basin.

Magnetic surveys estimate rock formations' characteristics and detect tectonic trends and unusual magnetic properties.
A detailed model of magnetic surveys aids in identifying geothermal reservoirs by revealing Curie isotherm depths.

Gravity surveys identify anomalies connected to deep magmatic bodies and fault structures where geothermal activities may occur.
It allows delineation of geothermal reservoirs by analyzing differences in density and assessing fault zones.

Sediment thickness ~10 km with geothermal gradients of 3.00 to 6.44 °C/100 m and heat flows from 45 to 90 mW/m².

Gradient variation from 20.84 to 52.11 °C/km and heat flows reaching 130.28 mW/m² indicate geothermal potential.

Generally low geothermal potential with heat flow ranging from 20 to 55 mW/m² as per literature.

Known springs include Rafin Rewa (42.2 °C), Ikogosi warm spring (54 °C), and Wikki spring.

Challenges include limited technological capacity, security issues, high costs of fieldwork, and ignorance of hydrogeological diversities.
Priority should be given to geothermal energy as a sustainable energy source to complement Nigeria's electricity supply.

Nigeria has abundant geothermal resources but requires effective modeling of subsurface structures for sustainable systems.
Magmatism influences heat flow, making geothermal energy exploration crucial to augmenting Nigeria's power generation and energy mix.