Computer Modelling of an Over-pressured Medium Enthalpy Geothermal Reservoir Located in Deep Sedimentary Basin

Over-pressure conditions occur in the southeastern regon of the Pannonian Basin due to the reversal of the regional tectonic stress beginning in the Middle Mocene. Exploratory wells in the area discovered well head pressures close to 350 bar and high temperatures exceeding 1 9 0 T at depth of 3,500 m. These promising shows, based on early appraisals, require thorough in depth investigations in terms of reservoir size, recoverable reserves, well deliverabilities in order to assess whether the resource could sustain feasible development issues for electricity production. The paper reviews the results of the preliminary reservoir simulation studies carried out for the area in question addressing reservoir evaluation: i.e. lateral extent, thickness and volume, tectonic features, governing boundary condtions, porosity/ permeability patterns, reservoir compartments and continuity between these compartments. INTRODUCTION The Pannonian Basin was formed as a result of a southward subduction of an oceanic lithosphere. The rising contact of the mantle with the crust resulted in crust thlnning by extension and erosion. This caused a Iugher than average heat flow in the region, due to the closer proximity to the hotter mantle. The subsidence which took place mainly the NeogeneQuaternary age. resulted in sedmentation of sandstones, clays and marl. The Pannonian formations overlie rocks of Mocene age or older. The latter are often referred to as basement and consist of both sedmentary and igneous rocks, includng limestones, dolomites, sandstones, conglomerates, as well as igneous and metamorphic rocks. The basement rocks are the main target of exploration for geothermal resources suitable for electricity production. Many of the deep geotheirmal reservoirs Pannonian Basin are overpressured with drilled in the south-eastem part of discovered high pressures exceeding 62 temperature of 190°C at depth of 3200m. gradients exceeding 21 MP;dkm. Exploratory