Petrophysical evaluation of the Lower Permian formation as a potential reservoir for CO2 - EGS – Case study from NW Poland.

Petrophysical evaluation of the Lower Permian formation was performed on the basis of the results of laboratory tests of rocks including pore space investigations using the Mercury Injection Capillary Pressure (MICP) method, the pore space saturation measurements by the Nuclear Magnetic Resonance (NMR) method, and measurements of the thermal conductivity coefficient by FOX series heat flow meters based on the one-dimensional Fourier equation. Three types of rocks: sandstones, conglomerates and effusive, sampled from the Ośno IG-2 well located in the Gorzów Block (NW part of Poland) were analysed. 42 core samples from the depth interval of 3212–3659 m bgl were tested. The results provide a wide range of information about the sample, primarily such parameters as pore size distribution, effective porosity and permeability, bulk density, sketal density, and thermal conductivity. The aim of the study was to determine the relevance of Lower Permian formation as a geothermal reservoir for CO 2 – EGS - Enhanced Geothermal Systems, which use carbon dioxide instead of water as working medium. Although worldwide research on such systems has been going on for many years, so far it has not been realized on a commercial scale. Moreover, to date there are no EGS installations in Poland. The ongoing research aims to bring the construction of the first pilot installation in Poland closer. Effusive rocks were characterized by lower value differentiation and relatively high lambda values (average 1.77–1.81 W/mK for dry samples, 2 W/mK for fully saturated and 2.1 W/mK for a mixture of water and CO 2), average effective porosity of 7.92% and permeability of 0.055 mD. Sandstones have the highest thermal conductivity values (1.87 W/mK at 20 °C, 1.87 W/mK at 50 °C, 1.82 W/mK at 100 °C and 1.79 W/mK at 150 °C), average effective porosity 5.56%, and permeability of 0.133 mD. For the conglomerates, the lowest values of thermal conductivity were obtained (average value for water-saturated sample equal 1.7 W/mK and for dry sample 1.4 W/mK). The average value of effective porosity for conglomerates is 7.66% and the permeability is 0.141 mD. The results indicate that the studied rocks have suitable parameters as a geothermal reservoir for CO 2 -EGS, especially effusive rocks. These parameters are similar to those of reservoir rocks for the EGS installation in Groß Schönebeck, as well as all types of rocks are classified primarily as petrothermal EGS. • Petrophysical parameters of the Lower Permian formation in the Gorzów Block are suitable for CO 2 -EGS. • Effusive rocks are characterized by the most suitable parameters as a geothermal reservoir for CO 2 -EGS. • Sandstones could also be potential reservoirs for CO 2 -EGS. • Conglomerates are characterized by the least suitable parameters as a geothermal reservoir for CO 2 -EGS. • The Lower Permian formation in the Gorzów Block has similar parameters to the Groß Schönebeck EGS reservoirs. [ABSTRACT FROM AUTHOR]