Geochemical and geomechanical effects of scCO(2) and associated impurities on physical and petrophysical properties of Permotriassic Sandstones (Germany): an experimental approach

摘要

Effects of impurities (SOx, NOx and O-2) from the extraction processes of the power plants in the scCO(2) fluids are studied with an experimental approach combining geochemical alteration in high p, medium T autoclaves, compressional tests in a heated triaxial testing device as well as geochemical and mineralogical analyses before and after the influences of distinct scCO(2) fluids on 140 x 70 mm sized samples of reservoir sandstones from the North German Basin (with carbonate cementation, silicate cementation and a combined silicate-carbonate cementation). On the background of variable lithological compositions, the attempt was made to normalize the scattering geomechanical data by the pure CO2-behavior measurement data to achieve a direct impression of any differences due to the impurities. Changes in the chemical composition of the saline fluids were systematically measured during the scCO(2) alteration experiments in the autoclave systems at distinct pT conditions. The development of the silica concentrations and of the pH value in the fluid solution during alteration showed a clear dependency on the fluid composition. Through systematical analysis of changes on the mineral surfaces using SEM microscopy images before and after scCO(2) + impurities alteration experiments or triaxial compression tests, corrosion effects were detected, but no differences which could be directly related to differences in the fluid composition could be identified. In all the types of sandstones, visible or measurable changes on mineral surfaces and pore fluid composition, respectively, take place as an interaction of rock with fluids of scCO(2) with and without impurities. Changing deformability and compressive strength of the rocks are the most apparent consequences due to these compositional changes. It is supposed that the chemical fluid differences are responsible for these changes. Also a specific distribution of the different fluids in the ambient pore space is indicated with even undetected consequences for the fluid influence on stress transmission and distribution within the grain structure. All work was performed within the project "CO2 purity for capture and storage (COORAL)" supported by the German Federal Ministry for Economic Affairs and Energy.