GENERAL INTRODUCTION

1.1 GENERAL OVERVIEW

Geophysical methods play a great role in exploration of geothermal energy.

Exploitation of geothermal resources for energy is common practice in areas where

geothermal gradients are high, such as tectonically active regions and in volcanic

areas e.g., Iceland and Italy (Yarima et al., 2013, Pasquale and vedoya, 2000). As

demand for sustainable energy increases, and the technology to harness it improves,

geothermal resources in relatively quiet regions prove increasingly viable.

Geophysical surveys are targeted at measuring the geophysical parameters of the

geothermal systems either directly from the surface of the earth or from shallow

depth. Recent works by Garba et al., (2012) have shown great potential for

geothermal heat flow in the Rafin Rewa. Hence, this study has been initiated to

gain insight into the geothermal prospect of the study area at Rafin Rewa, Dan-

Alhaji village using radiometric method. A geothermal system consists of the

following:

i.      A heat source,

ii.      A reservoir/rock,

iii.      A fluid which carries and transfers heat and a recharge area, Yasuka et al.,

(2005).

By far the biggest source of crustal heat is radioactive isotopic decay which, depending

upon geographic location, is estimated to generate up to 98% global heat, (Slagstad,

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2008). Other contributions, such as cosmic neutrino interaction with the Earth’s mass

(Hamza and Beck, 1972) and gravitational distortion (Beardsmore and Cull, 2001), are

likely to be very small indeed. The decay of the unstable isotopes of uranium (238U and,

to a far lesser extent, 235U), thorium (232Th) and potassium (40K) provide the largest

internal source of crustal heat that is geologically significant today (Brown and Mussett

1993). Using the heat production constant values, assumed or measured density (ρ,

kg/m3) and measured ppm concentrations of uranium (CU) and thorium (CTh), and wt.%

concentration of potassium (CK), the heat production rate (HPR) can be determined

thus:

HPR (μW/m3) = 10-5ρ (9.52CU + 2.56CTh + 3.48CK) (Rybach, 1988. Saleem,

2011)… (1)

The heat source is due to either radioactivity or active tectonics which represent major

zones of magmatic matter that is cooling (Uysal, 2009).

Radiogenic heat values in the crust in conjunction with heat flow density data, contribute to

our knowledge of the structure of the Earth’s lithosphere ( Taylor and Mcleriannan, 1985;

Beardsmore and Cull, 2001; Jaupart and Mareschal, 2003) and heat variation plays an

important role in crustal processes (Bea and Zinger., 2003; Sanderson et al., 2004). More

practically, areas of high heat production are increasingly being identified as possible

targets for hot, dry rock geothermal resources (Hasterok and Chapman, 2011). To this end,

radiogenic heat values have been calculated from a dataset of 400 points measured.

Geothermal energy is created by the heat of the earth. It generates reliable heat and emits

almost no greenhouse gases. It is a reliable source of power that can reduce the need for

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imported fuels for power generation. It is also renewable because it is based on practically

limitless resources. In addition, geothermal energy has significant environmental

advantages because geothermal emissions contain almost non chemical pollutants or waste.

This is especially true for geothermal energy representing a promising option for the

environmentally sound and secure generation of heat and electricity. They consist mostly of

water, which is re- injected underground. The Earth’s internal heat is derived from several