Abstract
Examples from the Polish clastic and carbonate reservoirs from the Central Polish Anticlinorium, Carpathians and Carpathian Foredeep are presented to illustrate possibilities of using well logging to geothermal resources recognition and characterization. Firstly, there was presented a short description of selected well logs and methodology of determination of petrophysical parameters useful in geothermal investigations: porosity, permeability, fracturing, mineral composition, elasticity of orogeny and mineralization of formation water from well logs. Special attention was allotted to spectral gamma-ray and temperature logs to show their usefulness to radiogenic heat calculation and heat flux modelling. Electric imaging and advanced acoustic logs provided with continuous information on natural and induced fracturing of formation and improved lithology recognition. Wireline and production logging were discussed to present the wealth of methods that could be used. A separate matter was thermal conductivity provided from the laboratory experiments or calculated from the results of the comprehensive interpretation of well logs, i.e., volume or mass of minerals composing the rocks. It was proven that, in geothermal investigations and hydrocarbon prospection, the same petrophysical parameters are considered, and well-logging acquisition equipment and advanced methods of processing and interpretation, developed and improved for almost one hundred years, can be successfully used in the detection and characterization of the potential geothermal reservoirs. It was shown that the newest (current investment)—as well as the old type (archive)—logs provide useful information.
Highlights
Sun and gravity determine almost all natural processes that occur on the Earth’s surface
Drying makes the rock cementation weaker which results in porosity increase, while at the same time high temperature causes the thermal increase of grains in the rock, making changes in strength and elastic moduli
Temperature is measured in boreholes, underground mines and on the Earth’s surface, but knowledge on the temperature is only from the nearest part of the Earth’s surface
Summary
Sun and gravity determine almost all natural processes that occur on the Earth’s surface. Only a small part of the solar energy is absorbed and sun heat penetrates a short distance, some tens of centimetres in the case of the daily cycle and a few tens of meters for the annual changes [1]. Temperature, reflecting the volume of heat in the body, influences rock properties and is of great importance in the development and utilization of hydrocarbon and geothermal resources and mining after the underground gasification of coal. Knowledge on the temperature is important to make the correction and work with real values of physical properties of rocks. Temperature is measured in boreholes, underground mines and on the Earth’s surface, but knowledge on the temperature is only from the nearest part of the Earth’s surface
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