In an effort to assess the seismic potential of geothermal plays in Dinantian carbonate reservoirs in the Netherlands and Belgium, geomechanical induced seismicity models were developed. However, the static elastic moduli E (Young's modulus) and v (Poisson's ratio) formation properties are required as input for these models. Due to the lack of available core plugs from wells in the area of interest and unsatisfying static-dynamic relationship in the literature, we designed a series of experiments to build a new static-dynamic relationship for Dinantian carbonates that take into account the effective confining pressure ((Equation)). The triaxial experiments were carried out on massive limestone and karstified dolostone collected in a quarry near the Belgium Dinantian geothermal play. The static and dynamic elastic moduli Es, Ed and vs, vd were measured at various (Equation) ranging from 1 to 35 MPa (mean effective stress in the geothermal reservoirs). We established the following relationships for the karstified dolostone:
(Equation)
And the massive limestone:
(Equation)
Geothermal heat is expected to become an important sustainable energy source to help reach the targets set by the National Climate Agreement of the Netherlands, which aims to reduce greenhouse gas emissions by 50% in 2030 and attain zero net carbon emissions by 2050. New geothermal plays, such as the Dinantian carbonates, are targeted to reach these objectives. However, they present geological characteristics quite different from the more conventional sandstone reservoir usually targeted in the Netherlands. The Dinantian carbonates are also heterogeneous and present various geological characteristics that affect the flow and mechanical properties of the reservoirs. In the southeast of the Netherlands, two geothermal doublets in the Dinantian have been stopped after a limited number of seismic events were recorded with a maximum magnitude of ML 1.7 (Baisch & Vörös, 2019). Seismicity has also been recorded in a Dinantian geothermal play near Mol in Belgium. Although the seismic activities were related to geothermal production, the causal mechanisms are still poorly constrained (Ter Heege et al., 2020).
