Determination of Geothermal Fields at Kızılcahamam (Ankara) Using Vertical Electrical Sounding (VES) and Spontaneous Potential (SP) Methods

Abstract

Geophysical exploration of geothermal resources deals with measurements on the physical properties of the Earth with two methods. First, the vertical electrical sounding (VES) method which is useful in determining the depth of overburden and depth, structure, and resistivity of flat-lying sedimentary beds and possibly of the basement also if it is not too deep. Furthermore the search for geothermal reservoirs normally involves resistivity surveying, and it is also employed routinely in groundwater exploration, which is of increasing worldwide importance. Second, spontaneous potential (SP) method is applied for determining the possible faults and finding the places with and without the liquid flow in the study area. At the SP graphic is analyzed that the natural voltage in a few measuring points varied between +28 mV and −48 mV values. At the natural potential, the plus (+) and minus (−) transitions indicate faulting zone. In this work, VES and SP methods at Kızılcahamam (Ankara) geothermal area were used to delineate location of aquifer zones and site wells or estimate properties of the system. Schlumberger electrode arrays were used in the VES measurements at 60 point in the study area. Schlumberger soundings at the study area have been carried out to try and estimate the bedrock resistivity at different depths. The measured quantity at the study area was called apparent resistivity. Interpreting the resistivity data consists of two steps: first, a physical interpretation of the measured data, resulting in a physical model, and second, a geological interpretation of the resulting physical model. The resistivity structure at study area is dominated by two coherent low resistivity layers that underlie most of the field. The shallower layer (<10 Ωm) lies within 300 m depth, while the deeper one is at about 900 m depth. Resistivity of rocks depends on porosity, saturation, content of clay, and resistivity of pore water. As a result of all these studies, geothermal anomalies having low resistivity values at the five different VES points have been identified. For geothermal drilling of the suggested VES, points constitute the appropriate fields.