engleski

Geothermal Potential Assessment of the Gas Fields in Central Drava Basin in Republic of Croatia Due to Exergy Analysis

Objectives: In Croatia there is a urgent need to improve energy balance with more efficient methods of energy resources exploitation. With energy utilization, particularly for geothermal reservoirs, it is necessary to interconnect three indexes for possible production and consumption. These are functionally interdependent variables of financial, political and legislative issues which are in econometrics generally called economical indicators. Therefore, sustainability of production and future development depends upon the interaction of geoscientific and economical factors which must be simultaneously determined. It is important to propound that in Croatia there are approximately thousand wells drilled on oil, gas/condensate and geothermal reservoirs, of which only 50 was primarily drilled for purpose of geothermal exploitation. Over ten thousand seismic measurements where made. Most of the drilled wells are scheduled for permanent abandonment in the near future, because of economical reasons and technological limitations of further oil&gas recovery. However, partially well abandonment is possible to stop by reassigning it into geothermal wells, if aquifer's water temperature and flow are satisfactory. Methods: By the cause of various reservoir regime conditions in the eruptional phase, unsuited equipment, poor injection regimes in secondary phases, remarkable quantities of petroleum and gas stay trapped or by-passed in the reservoir. The percentage of water in overall petroleum production becomes so high that the further classic production has no economical justification. By reassignment of wells in the first phase the primary product is still gas and the geothermal water is secondary. In the second phase of production, geothermal water is produced with small part of natural gas, so the petroleum reservoir becomes geothermal one. This production phase unveils all production intervals with no consideration of heterogeneous, hydrodynamic and other reservoir conditions. By injection of produced and additional quantities of fresh water into the injection well, the eruption mode of production is maintained. These scientific presumptions are beneficial to identify correlation between sustainability and renewability of gas aquifers in Central Drava Panon basin in ending state of production. With complex modelling of each reservoir through exergy degradation principle, as well as applied First and Second Law of Thermodynamics, it is possible to determined reservoir geothermal potential. This scientific method is associated with reservoir engineering management to optimize production in the well and surface equipment by means of pressure and temperature changes in distinctly conditions of exploitation. Heat energy output, number of wells and method of injection will depend upon technical-technological solutions of re-assigned wells and economy needs in the reservoir surrounding. Results: Primary scientific objective of this paper is to determine an optimal exploitation conditions and initial reservoir parameters in view of technological, economical, social and other aspects that define balance between sustainable development and energy renewability. By production completion and re-allocation of perspective gas reservoirs in the next decade (Molve, Kalinovac, Stari Gradac), with suitable flow of geothermal water and thermal characteristics, potentially it could be obtained more than 100 MW of heat energy and 10 MW of electric energy. Conclusions: The commitments for Croatia admittance in EU are not possible to be accomplished without the environment preservation according to the sustainability development principles. In Croatia there are still no concrete mechanisms of economical adjustment to cleaner production and decrement of energy consumption per unit product. Regarding this problem it is necessary to significantly improve management of natural energy mineral resources with "on the source" method. Entrance in the EU means unconditional acceptance of measures and standards, which in the segment of renewable sources means increment of their share in total energy balance up to 12% by 2010. Future utilization of abandon oil and gas wells, for the purpose of geothermal power production, will undoubtfuly lead Croatia closer to EU standards.

geothermal energy; aquifers; abandon oil and gas fields

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