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Investigation of the seasonal variations of the aquifers temperature in Messara plain

Boutsakis Konstantinos

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Summary

The utilization of renewable energy sources is aimed globally. In recent years, considerable efforts have been made to identify, systematically record and partly exploit the geothermal resources in the Greek area. Despite this, there are only few data on the potential geothermal fields in Crete. Apart from some evidence in Eastern and Western Crete, in the region of Messara in Central Crete, have been noted increased temperatures in water wells. The increased temperature of the waters in drillings, that has been measured both in summer time (dry season) and in winter time (wet season), is an indicator of the existence of geothermal fields in this particular region of Messara.In the search for further information on the potential geothermal fields in Crete, samples have been collected of seven wells in the Messara region for geochemical analysis. The present diplomatic thesis firstly deals with the presentation of the results of the analysis of the chemistry, the characterization of the water quality and the comparison between two different periods (dry and wet). At the same time, with the support of geological data, specific geothermometers are utilized. The two potential geothermal reservoirs are located within the Alpine formations and may well also within the carbonate formations of the Tripolis Zone.In conclusion, the values that resulted from the measurements, analyses and calculations can be summarized as follows:Measurements of water temperatures of wells:Peri 1 (6/2015): 20,9 οC, (2/2016): 20,7 οC,Peri 2 (6/2015): 27,3 οC, (2/2016): 27,7 οC,Peri 3 (6/2015): 22,4 οC, (2/2016): 22,0 οC,Platanos 1 (6/2015): 26,4 οC, (2/2016): 27,6 οC,Platanos 2 (6/2015): 21,4 οC, (2/2016): 22,1 οC,Melidochori 1 (/7/2015): 23,1 οC, (2/2016): 23,2 οC,Melidochori 2 (7/2015): 23,5 οC, (2/2016): 24,8 οC• The range of the values of pH during the dry season in wells is varies from 7.25 to 8.04, while during the wet season varies from 7.33 to 7.76. Therefore, water is characterized as alkaline and emanates from a "new" relatively aquatic mass.• The range of the values of electrical conductivity in the samplings regarding all drillings varies from 694-1987 mS/cm. That indicates increased quantities of salts in water.• In accordance with the water hardness, the water in well Platanos 2 is characterized as ‘moderately hard’ while in the other wells as ‘hard’.• Based on the Revelle coefficient values the groundwater is characterized as ‘good without seawater penetration’.• From the Na / K ratio values, sampled during the wet season, in wells Peri 1, Platanos 2 water is described as ‘meteoric’ and in well Platanos 1 water is in the aquifer recharge area. In contrast with the above, the sample of the water in the wells Peri (1, 2 and 3) and in Melidochori 1 during the dry period, are in discharge area by adsorption Na+ and in well Platanos 2 water is designated as ‘meteoric’.• The Mg/Ca ratio values are less than 0.7 so there is no sea water penetration and water also comes from limestone aquifers, excepting the value of well Platanos 2 which is slightly greater than one. That means that the water comes from ophiolithic aquifers formations or generally silicate-rich Mg2+.• According to the ratio Cl/SO4 in the sample collected during the wet period, water can be characterized as ‘sulphide-chloride’ in the drillings of Peri 2, Melidochori 1 Melidochori 2. In the wells Peri 1, Peri 3, Platanos (1 and 2) water is characterized as ‘chloroSulphenated’ . In the sample collected during the dry season, water in wells Peri 1, Peri 3 and Platanos 2 is characterized as ‘chloroSulphenated’ , whereas in the others as ‘sulphide-chloride’.• The ratio of (Ca+Mg)/(Na+K) is above one to all wells in both samples taken and indicates that there is an aquifer with constant recharge.The temperature of the potential geothermal reservoirs resulted utilizing various standard geothermometers:• In the area of Melidochori, the range of the values of the potential geothermal reservoir is 70-170oC and was a result of the use of geothermometers Na/K. In the area of Peri – Platanos, the range of the values of the potential geothermal reservoir 90-380oC. This type of the geothermometers that were used, provides reliable results for values above 180oC.• Using geothermometers K/Mg, in the area of Melidochori, the resulting values of the potential reservoir temperature were 70-90oC and in the areas of Peri and Platanos were in the range of 50-90oC. Samples of these areas contain Mg2+ concentrations exceeding the level of 1 ppm.• Similar issues occur also with the silicon geothermometers, resulting very high temperature values to the potential reservoirs with maximum temperature up to 170oC.In conclusion, we consider that the most reliable geothermometer is that of the Na-K-Ca. After the suggested corrections in the magnesium values, the temperature of a potential reservoir in the area of Peri - Platanos are estimated at 60oC and in the area of Melidochori at 50oC.

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