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

Hydrochemical characterization of a mine water geothermal energy resource in NW Spain

Abandoned and flooded mine networks provide underground reservoirs of mine water that can be used as a renewable geothermal energy source. A complete hydrochemical characterization of mine water is required to optimally design the geothermal installation, understand the hydraulic behavior of the water in the reservoir and prevent undesired effects such as pipe clogging via mineral precipitation. Water pumped from the Barredo-Figaredo mining reservoir (Asturias, NW Spain), which is currently exploited for geothermal use, has been studied and compared to water from a separate, nearby mountain mine and a river that receives mine water discharge and partially infiltrates into the mine workings. Although the hydrochemistry was altered during the flooding process, the deep mine waters are currently near neutral, net alkaline, high metal waters of Na-HCO3 type. Isotopic values suggest that mine waters are closely related to modern meteoric water, and likely correspond to rapid infiltration. Suspended and dissolved solids, and particularly iron content, of mine water results in some scaling and partial clogging of heat exchangers, but water temperature is stable (22 °C) and increases with depth, so, considering the available flow (> 100 L s− 1), the Barredo-Figaredo mining reservoir represents a sustainable, long-term resource for geothermal use

Review and implications of relative permeability of CO2/brine systems and residual trapping of CO2

The adoption of carbon capture and storage (CCS) as a method of mitigating anthropogenic CO2 emissions will depend on the ability of initial geological storage projects to demonstrate secure containment of injected CO2. Potential leakage pathways, such as faults or degraded wells, increase the uncertainty of geological storage security. CCS as an industry is still in its infancy and until we have experience of industrial scale, long term CO2 storage projects, quantifying leakage event probabilities will be problematic. Laboratory measurements of residual saturation trapping, the immobilisation of isolated micro-bubbles of CO2 in reservoir pores, provides an evidence base to determine the fraction of injected CO2 that will remain trapped in the reservoir, even if a leakage event were to occur. Experimental results for sandstone, the most common target lithology for storage projects, demonstrate that 13–92% of injected CO2 can be residually trapped. Mineralisation, the only other geological trapping mechanism which guarantees permanent trapping of CO2, immobilises CO2 over hundreds to thousands of years. In comparison, residual trapping occurs over years to decades, a timescale which is more relevant to CCS projects during their operational phase and to any financial security mechanisms they require to secure storage permits

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

Combining ground stability investigation with exploratory drilling for mine water geothermal energy development. Lessons from exploration and monitoring

No abstract available

GIS analysis for the selection of optimal sites for mine water geothermal energy application: a case study of Scotland's mining regions

Water within flooded coal mines can be abstracted via boreholes or shafts, where heat can be extracted from (or rejected to) it to satisfy surface heating (or cooling) demands. Following use, water can be reinjected to the mine workings, or discharged to a surface water receptor. Four criteria have been applied, using ArcGIS, to datasets describing mine workings and mine water below the Midland Valley of Scotland, to provide an initial screening tool for suitability for mine water geothermal energy exploitation. The criteria are: (i) presence of two or more worked coal seams below site, (ii) absence of potentially unstable shallow (<30 m) workings, (iii) depth to mine water piezometric head <60 m, (iv) depth of coal mine workings <250 m. The result is the Mine Water Geothermal Resource Atlas for Scotland (MiRAS). MiRAS suggests that a total area of 370 km2 is “optimal” for mine water geothermal development across 19 local authority areas, with greatest coverage in North Lanarkshire. This result should not be taken to suggest that mine water geothermal potential does not exist at locations outside the identified “optimal” footprint. The MiRAS does not preclude the necessity for specialist engineering and geological input during full feasibility study