Steady-State CO2–Brine Relative Permeability and Hysteresis in Stenlille Sandstone

Abstract

Creating a single, “global” relative permeability set for any storage site is challenging due to pronounced vertical heterogeneity and differing rock types across layers. In this work, six sets of steady-state (SS) relative permeability measurements were performed on two reservoir core samples following three successive steps: primary drainage, imbibition, and secondary drainage. These steps were conducted at reservoir conditions of 160 bar and 50 °C for two sandstone cores from the Stenlille-6 well, Gassum formation in the Stenlille gas storage area, onshore Denmark. Steady-state data were acquired using a setup with a separator located inside the oven, enabling saturation measurements under reservoir conditions. The two steady-state experiments were conducted under identical pressure, temperature, and flow-rate conditions, but on cores with different permeabilities, which resulted in various capillary numbers. With the capillary number in the transition zone, near the viscous limit, the data are comparatively insensitive to specific experimental conditions and align with relative permeabilities reported for other sandstones under similar test conditions (103–207 bar and 38–91 °C) in the literature. This makes them suitable as “reference” relative permeability functions for the Stenlille sector model. The experiments provide important insights into the effects of CO2 trapping and hysteresis during different flooding stages. The steady-state data were history-matched using numerical simulations through inverse numerical modeling. The history-matched data for relative permeability are similar to the Brooks-Corey equations that solely fit the experimental data without considering capillary pressure using Darcy’s law, indicating that no further history-matching was needed and highlighting the negligible effect of capillary pressure on the presented experimental data.