Facies Variations Detected by Well Log Correlation in a Geothermal Reservoir (Újfalu Formation) around Debrecen, Hungary

A sequence stratigraphy based well-to-well correlation was performed as part of a regional geothermal project to determine the geometry and hydrogeology of a reservoir from which two famous spas produce thermal water. The most important thermal reservoir in Cenozoic formations in Hungary is the Újfalu Formation, which was mainly deposited in a delta front environment. In this paper a facies variation is presented in the Újfalu Formation, above a thrust wedge of the basement. Parasequences were determined by well log correlation, the appearance of parasequences is different in the sub-basins (sandy) and above the thrust (silty with sand layers). The silt and clay deposits in the reservoir decrease the hydraulic conductivity, modify the water movement. The difference could be formed by the relative vertical movement of the thrust during the deposition and local character in the surroundings of it. This information refines the sub-regional solid and hydrogeological model, thus helps the sustainable, economic and various utilization of geothermal energy in a famous thermal bath area.