Abstract
Gamma-ray spectrometry is a surveying technique that allows the calculation of the heat produced during radioactive decay of potassium, uranium, and thorium within rock. Radiogenic heat producing rocks are often targets for geothermal exploration and production. Hence, refinements in gamma-ray spectrometry surveying will allow better constraint of resources estimation and help to target drilling. Gamma-rays have long half-lengths compared to other radiation produced during radiogenic decay. This property allows the gamma-rays to penetrate far enough through media to be detected by airborne or ground based surveying. A recent example of ground-based surveying in Scotland shows the ability of gamma-ray spectrometry to quickly and efficiently categorize granite plutons as low or high heat producing. Some sedimentary rocks (e.g., black shales) also have high radiogenic heat production properties and could be future geothermal targets. Topographical, atmospheric and spatial distribution factors (among others) can complicate the collection of accurate gamma-ray data in the field. Quantifying and dealing with such inaccuracies represents an area for further improvement of these techniques for geothermal applications.
Highlights
In this paper, we review gamma-ray spectroscopy as a survey tool for geothermal resource exploration
Uranium, and thorium are of particular interest for geothermal production because they contribute significantly to the heat produced during radioactive decay in the rock
The concentrations of these elements show an approximate trend to increase with silica content [28]; the same relationship has been found for gamma ray intensity in volcanic rocks [29]
Summary
We review gamma-ray spectroscopy as a survey tool for geothermal resource exploration. Clyde Plateau Lavas in the Midland Valley of Scotland would likely not be effective caprocks, in this case due to extensive fracturing Where such duvet rocks cap highly radiogenic granite, vastly enhanced heat can be obtained [8,9,10]. Gamma-ray surveying has a wide range of applications beyond geothermal exploration including: uranium exploration [18,19], sedimentary facies identification for oil and gas exploration [20,21,22], detection of radioactive contamination [23,24], and mineral exploration [25] It can be used for pure earth science discoveries, e.g., constraining deep crustal processes from potassium, uranium, and thorium concentrations in modern day outcrops [26,27]
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