Objective and hypothesis
The main purpose of this study is to examine the effect of residual hydrocarbons in non-flooded and water-flooded chalk reservoirs on supercritical (sc) CO2 injectivity. This will be achieved through a thorough characterisation of the residual hydrocarbons in core and cuttings samples from the Maastrichtian chalk reservoir of the Halfdan and Dan chalk f ields. The project will in detail investigate the distribution of residual oil fractions in the reservoir, and the effect of the residual hydrocarbons in non-flooded and water-flooded chalk reservoirs on scCO2 injectivity. The project will help de-risk depleted oil field CO2 storage sites and may have a substantial impact on CO2 and emission reduction.

Approach
In WP1, the project will conduct scCO2-flooding experiments on core samples at reservoir conditions at GEUS Core Analysis Laboratory. The flooding experiments will, in combination with laboratory analyses before and after f looding, investigate the impact of scCO2 interaction on the residual hydrocarbons in the chalk matrix of rock samples. WP2 will analyse core and cuttings samples at AU’s LOC laboratory and compare pre- and post-flooding samples to quantity movable, semi-movable, and non-movable oil fractions and solid bitumen in the reservoir together with detection of changes in hydrocarbon composition induced by scCO2 flooding. Finally, WP3 will prepare sample pellets for reflected light microscopy to describe residual hydrocarbons in pre- and post-flooding samples.

Expected impact/output
The results on specific risks for residual hydrocarbons movability/clogging will translate directly into the decision-making process of the applicability of a depleted chalk reservoir as a storage site. It will further address issues related to potential leakage due to CO2-induced hydrocarbon movability. The project will help de-risk depleted oil field CO2 storage sites and may thus have a substantial impact on emission reduction and thus on reaching the goal of atmospheric CO2 reduction in Denmark.