Temperature Analysis Of Tinggi Raja Geothermal Reservoir, Simalungun District

Reservoir temperature measurements have been carried out using the empirical geotermometer method at the High Raja Geothermal Simalungun district in order to determine the value of the High Raja geothermal reservoir temperature. The study was conducted using the Na-K geotermometer method, the Na-K-Ca-Mg geotermometer, a Na-K-Ca-Mg geotermometer to obtain the temperature value of the geothermal reservoir. The results of the study Based on the empirical Geotermometer equation show the surface temperature of hot water at three points showed that at the point I obtained hot water surface temperature of (65.0 ± 0.5°C) with a surface pH of 5.2 hot water, point II the hot water surface temperature of (65.0 ± 0.5°C) with a large surface pH of hot water 5.8, and point III the surface temperature of hot water is (63.0 ± 0.5°C) with a large pH surface of hot water 5.8. The average concentration of chemical elements contained in hot water samples include Ca for (255.33 mg / L), K for (150 mg / L), Mg for (43.63 mg / L), Na for (34, 13 mg / L) and the average temperature of the reservoir that can be received using the Na-K-Ca Geotermometer is a temperature of 182.89921°C


Introduction
North Sumatra is one of 33 provinces in Indonesia, has total area of 181,860.65 km² which consists of 71,680.68 km² or 3.73% of the total area of the Republic of Indonesia. Geographically, North Sumatra Province is located at 1 ° -4 ° North Latitude and 98 ° -100 ° East Longitude. North Sumatra Province consists of 25 districts and 8 cities, 421 sub-districts and 5828 villages. One of the districts in North Sumatra is Simalungun.
Geologically, Indonesia is located on three plates namely the Eurasian Plate, the Indo-Australian Plate and the Pacific Plate causing Indonesia to have abundant mineral reserves, has many active volcanoes that have the potential to cause eruptions and cause areas that are often subject to earthquake, tsunami and ground movement or the so-called landslide. Thus, North Sumatra is very prone to disasters both from volcanic and tectonic activities. While climatologically, located around the equator will cause changes in weather.
Geothermal water source in Simalungun Regency, geographically located between 02036'00 "-03018'00" North Latitude and 98032'00 "-99035'00" East Longitude. Based on what happened at the Tinggi Raja geothermal source, there was a change in the environment due to the transfer of hot water sources that caused changes in temperature. Then it is necessary to re-measure the temperature of the geothermal reservoir which will then be analyzed the impact of changes in the temperature of the geothermal reservoir.
Indonesia has a great wealth of environment and natural resources, but people tend to underestimate it and regard it as reasonable. Understanding the environment that all objects and conditions, including humans and their activities, are contained in the space in which humans are and affect the survival and well-being of humans and other living bodies. Massive environmental damage in various places in almost all parts of the country shows that the ability of the Indonesian people in managing the environment or common property resources is very weak. This also shows that from the national to the communal level there has been damage to cultural values. The various human activities ultimately indicate an increase in land requirements which also has an impact on the reduced level of existing vegetation. According to the Environmental Protection Agency (2009) in 2005, this effect is a major problem in every developing city in the world towards global warming. Geothermal is one of the alternative renewable energy sources and has the potential to be produced in Indonesia, this is because Indonesia has a circle of volcanic belts along more than 7000 km which has a large geothermal potential. The heat energy that comes from inside the Earth will come to the surface and will be collected in parts of the Earth's crust. The Earth's crust is composed of various types of rock that have different melting points. Rocks that cannot stand the high temperatures of the Earth's core will melt and become a liquid called magma. This energy directly comes from terrestrial heat sources which are basically endless under the Earth's crust and do not depend on direct solar energy. Temperatures under the Earth's crust which are relatively thin can reach 1300 o C.
Geothermal (geothermal) is a natural resource in the form of hot water or steam that forms in the earth's reservoir through heating underwater surface by hot rocks. Geothermal system is one of the systems that occur in the geological process that runs in the order of hundreds or even millions of years which today brings benefits to humans both exploited by making manifestations for tourism and their use for agriculture and animal husbandry.
Geothermal method is one method for calculating the temperature of a reservoir that is in a heat source by using a thermometer as a comparison tool and the object of measurement is the content of chemical elements present in the water. How to explore the geothermal system has been done a lot. From geotermometer measurement data can be measured hot water chemistry such as Na, K, Mg, Ca. Based on these geothermometer measurements, the results for reservoir temperatures are based on chemical elements present in hot water, which can ultimately be formulated into the geothermometer equation.
The research is important because the geothermal temperature measurement data can change due to natural changes. Therefore we need new data to observe changes from the previous data. Research on determining the temperature of the geothermal reservoir using empirical geotermometer equations have been carried out such as in the Rianiate geothermal area of Pangururan District producing a reservoir temperature of around 100,480 C and Dolok Marawa geothermal area in Simalungun Regency with a reservoir temperature of around 125,100 C. However, the source displacement occurred hot water in the area, the authors are interested in re-measuring reservoir temperatures using the empirical geothermometer equation.
With this description so the author chose the title: Environmental Analysis of the Impacts of Temperature Changing of the Tinggi Raja Geothermal Reservoir in Simalungun Regency, to determine the impact of changes that occur in the geothermal reservoir.

Sample Testing Result
Sample testing is carried out in the Medan Industrial Research and Development Agency testing laboratory, namely testing the chemical elements Na, K, Ca, and Mg on the sample. Samples were taken from the three observation points where each point was taken as much as one sample of hot water. The results obtained can be seen in the table below.

Calculation Result of Reservoir Temperature
To find out the reservoir temperature in the study area, it will be analyzed using the Na-K geothermometer equation, Na-K-Ca geothermometer, and Na-K-Ca-Mg geothermometer. From the measurement results using the equations of each empirical geothermometer the temperature results are as follows:

Empirical Geothermometer Discussion
Based on the table, the temperature for the Na-K geothermometer equation obtained at 1754.79⁰C, while the temperature used with the Na-K-Ca geothermometer was 182.89⁰C. Whereas with the Na-K-Ca-Mg geothermometer a temperature of 3729,27 o C obtained. Compared with the data from the previous research conducted by Adelina Tambunan in 2010 with the results of the study using a Silica geothermometer of 125,10 o C, with the Na-K geotermometer equation of 336.69⁰C, and with the Na-K-Ca geotermometer equation of 1240.30⁰C.