Abstract:
Assessing geothermal potential is a difficult task. It is a time and money consuming process. There are many methodologies, such as deep drilling bore holes and measure temperature by using thermal sensors, silicon solubility measurement, magneto telluric, etc.
The used equipment for these methods, especially for drilling of deep bore holes are much expensive. If geothermal gradient is very low, the area cannot be effectively used to establish a geothermal power plant. Another method based on contents of amorphous silica in hot spring water is also used to determine the geothermal gradient. Main task of this study is to find a suitable cost effective method to assess the geothermal potential in Sri Lanka and to develop a lab scale plant. As a cheaply available geophysical technique, ground resistivity measurement was also used to measure the temperature. Increasing temperature again increases their resistance. This natural phenomenon has been used to develop a methodology to assess the geothermal potential in various countries.
Resistivity surveys have been carried out in various places in Sri Lanka. Gathered resistivity data has been analyzed. Geothermal gradient calculation was done in Bogala Graphite Mines to study about the temperature gradient in Sri Lanka. Also this selected place was far away from hot spring areas and hence those hot springs had no influence to the collected data. This method is suitable to find temperature gradient of Sri Lanka. The average values of temperatures in those levels were computed and then geothermal gradient was calculated which is 28.0460C/km. This method gave some reliable information as to how the temperature gradient varies at crustal level of rocks in Sri Lanka.
To calculate power generation, a laboratory model was developed with the possibility of applying varying parameters. Collected the annual average temperature data and predicted the temperature gradient of various districts. According to the calculations done, geothermal gradient in Sri Lanka is varying between 23 0C and 30 0C per km. This information has been used to develop the geothermal map of Sri Lanka.
Laboratory plant was developed and its performances were studied for varying hot spring temperatures and all data gathered and analyzed. According to that the geothermal temperature gradient in Sri Lanka is suitable to generate electricity. But the water flow rate is not sufficient to produce more power.
