Datensatz

Zusammenfassung

The electrical rock conductivity is a sensitive indicator for CO2 migration processes. CO2 dissolves into the pore water in large amounts and provides additional charge carriers due to the dissociation of carbonic acid. We present laboratory measurements of the spectral complex electrical conductivity of water-bearing sand samples during exposure to and flow-through by carbon dioxide. Pressures up to 300 bar and temperatures up to 80°C were applied. Steady-state experiments serve for investigating the physicochemical equilibrium of the fluid phases. Dynamic experiments aim at analyzing the impact of partial saturation and chemical interaction on complex conductivity. The steady-state dissolution experiments show that besides the conductivity-increasing dissociation a second opposing process may be observed which results in a significant reduction of conductivity at high salinities despite the added CO2. We explain our observations with a semi-analytical formulation for the electrical conductivity taking into account the interactions of ion and neutral species. A significant reduction of saturation is observed during CO2 flow and drainage. The spectral complex conductivity maps both changes in saturation and chemical interaction. recovery usually take place on active or abandoned oil respectively gas fields. Considering the amount of steel infrastructure in the subsurface of these investigation sites it is crucial to take account of the effect of steel infrastructre on electromagnetic fields. Therefore we present three-dimensional finite element (FE) simulations of transient electromagnetic fields in the present of steel infrastructure. As a first approach we consider two common scenarios. The first scenario covers the case of surface transient electromagnetic measurements with a crossing pipeline beneath a receiver profile. The second scenario covers borehole transient electromagnetic measurements in a partially steel cased borehole. We demonstrate that steel infrastructure has a significant effect on the electromagnetic response.