Hydraulic connectivity in Pannonian sandstones of the Mezőberény geothermal doublet

The geothermal doublet at Mezőberény in SE Hungary has suffered from poor productivity and injectivity since it began operation in 2012. The injection and production wells of the doublet are near vertical and have ~400 m production interval, consisting of few thin sandstone bodies in a shale matrix. Previous studies have considered chemical factors, such as scaling and clay mobilisation, as possible causes of injectivity and productivity limitations. So far, however, the possible impact of poor hydraulic connectivity on these limitations has not been considered. Therefore, a geological model describing the geometry of the sandstone bodies in the aquifer and its net sandstone content have been derived in this study. The model is based on a geological dataset from the Békés Basin including core samples, 2D seismic lines and Gamma Ray logs of nearby petroleum wells. Dozens of aquifer realisations of this model were generated, which capture the sedimentary architecture of the aquifer utilising an object-based modelling approach. For each realisation, the volume of sandstone bodies that both wells intersect was calculated. We found that only a small percentage of the total sandstone volume in the realisations was intersected by both wells. This indicates that the net aquifer volume is most likely much smaller than the net-sandstone content of 11% that was derived from the well logs. Therefore, these results suggest that it is likely that hydraulic connectivity is poor between the injection and production well in the doublet, limiting injection and production rates. In addition, our results highlight the importance of sedimentary facies analysis as a tool for successful exploitation of geothermal resources.