Supercritical CO 2 core flooding and imbibition in Tako sandstone—Influence of sub-core scale heterogeneity

Abstract

This paper presents a numerical simulation study of a full CO 2 core flooding and imbibition cycle performed on a heterogeneous Tako sandstone core (measured 14.5 cm long and 3.68 cm in diameter). During the test, supercritical CO 2 (at 10 MPa and 40 °C) and CO 2-saturated brine was injected into one end of the horizontal core and a X-ray CT scanner (with a resolution of 0.35 mm × 0.35 mm) was employed to monitor and record changes in the fluid saturations, which enabled 3D mapping of the saturation profiles throughout the core during the course of core flooding test. The CO 2 flooding test demonstrated that (1) sub-core porosity heterogeneity had a marked impact on the CO 2 migration pattern within the Tako sandstone core at low injection rates (∼0.1 cm 3/min); (2) the influence of the porosity heterogeneity on the mean CO 2 saturation profiles along the core became gradually diminished as the injection rate was increased in steps to 3 cm 3/min. The numerical simulation results have shown that the immiscible displacement processes in the heterogeneous Tako core could not be adequately described by using a single capillary pressure curve in a 1D model of the core. This was found to be the case even when a 3D model (5 × 5 × 24) was used, where the porosity/permeability heterogeneity across the cross-sections, as well as along the core, was taken into account. Furthermore, the apparent correlation between the CO 2 saturation and the porosity (mean) profiles during the CO 2 flooding could largely be accounted for by employing a Leverett J-function type scaling factor, which reflects the influence of porosity/permeability heterogeneity on the capillary pressure.