Geothermal Potential of the Ortahaza-West Field in Hungary

Abstract

The Hungarian petroleum industry has always participated in the utilization of favourable geothermal conditions in the country. Most of the Hungarian geothermal wells were drilled by MOL Ltd. as petroleum prospect holes. Accordingly, the field of geothermics belonged to the petroleum engineering, although marginally. It was therefore a surprise to hear of the decision of MOL Ltd. to build a geothermal power plant of about 2-5 MW. The tender was published in 2004. The site selected for the geothermal project is near the western border of a Hungarian oilfield, close to the Slovenian border. The location of the planned geothermal power plant was chosen after an analysis of suitable wells owned by MOL Rt. The decision was made on the bases of different reservoir data. The existence of a reservoir of the necessary size, temperature, permeability, productivity and water chemistry data was proved. The wells provide enough information to understand the character of the reservoir and will be the production wells used by the planned power plant. The depth of the wells is in the range of 2930 - 3200 m. The Triassic formation is reached at around 2851 m. Production and injection wells are planned. The primary objective of the evaluation is to further learn the nature of the geothermal system. First a one-day discharge test is carried out. If this short-term test is successful, a six-months long-term discharge test will follow. The first period of the test is a transient phenomenon. During the well test, the wellhead pressure, flow rate, outflowing water temperature, dynamic fluid level, and chemical components will be measured. The heat transfer around the borehole is influenced by the flow rate and the time. For the proper interpretation of the measured data it is very important to analyse the heat transfer processes around the borehole. The measured data from the experiments must also be fitted into the framework of a mathematical model in order to form a coherent system. Before the drilling operations and the discharge tests, the temperature of the outflowing water can be predicted. This is made possible by applying recently elaborated simulation methods (Bobok-Tóth 2003, Tóth 2004). The available thermal power of a simple doublet can also be determined.