Impedance Spectroscopy (IS) for Assessing the Wetting Conditions of Reservoir Rocks
The wetting conditions of reservoir rocks influence important reservoir characteristics like relative permeability, residual oil or water saturation. In this project we studied, if Impedance Spectroscopy (IS) can provide a characterization of the wetting state. We first examined numerical model systems of water filled connected pores considering the electrical double layer at the fluid rock interface. The resulting understanding of the system was used to design an experimental study, conducted on a reference system of sintered borosilicate samples. These experiments were conducted in parallel with measurements on reservoir rocks, which conclude our study. Both the numerical simulation and the measurements on synthetic samples show that qualitative wettability information can be derived from IS data for rocks with sufficiently fine pores and low saline pore water. The presence of IS effects in low saline environments can be confirmed for reservoir rocks, allowing for an application e.g. in the context of “low salinity flooding”, even though not for high salinity reservoir conditions. This project is funded by DGMK (German Society for Petroleum and Coal Science and Technology).
Figure 1: Micro-scale simulation of SIP properties. The coupled ion migration and diffusion processes are solved at the pore space using the finite element program COMSOL Mutiphysics. a) 3D excess charge density distribution; b) IS response of the pore
Figure 2: IS phase maximum Φmax, depending on pore size R and fluid salinity σfluid for a) water wet and b) oil wet reference samples. Water wet samples show significantly stronger IS signals.