Impact of Rock Elastic Properties on Fracture Geometry in Potential Enhanced Geothermal Systems in Poland

In hot dry rocks (HDRs), hydraulic fracturing is necessary to create enhanced geothermal systems (EGSs) and optimize flow rates between injection and production wells. The geometry of the induced fracture is related to numerous factors, including rock mechanical properties, especially Young’s modulus and Poisson’s ratio. In this paper, we show the influence of Young’s and Poisson’s parameters on fracture geometry in selected HDR-type prospective areas in Poland. Parameters were determined in the laboratory based on drill core samples from granite and sandstone formations using both dynamic and static methods. The results obtained reveal strong differences between dynamic and static values in granite and less diverse results in sandstone. Based on these data, numerical simulations of fracture geometry were carried out, taking into account the variability in the rocks’ elastic parameters. Sensitivity analysis showed that relatively high diversity in the elastic parameters led to a relatively slight impact on the fracture geometry of the tested formations. The influence of Young’s modulus did not exceed 6.5% of the reference half-length and width values for sandstone and 7.3% of the half-length for granite. Variability in the fracture width was significant in granite formation and amounted to 46.4%. The influence of Poisson’s ratio was marginal in both tested types of rocks. The research results, which have not been reported previously, can be considered for the design of hydraulic fracturing operations in enhanced geothermal systems in Poland.