Project Wintershall: Chalk compatibility to CO2-enriched water injection and further reduction of Sor

minimal; at that point, the outlet stream was redirected to the sampling loop. Geochemical analysis was conducted on effluent samples from both experiments to investigate potential mineral reactions with the injectant fluid. Geochemical results of the WINZ-1 experiment suggested a CO2 consumption of approximately 3%, and mineral analysis of the produced effluent sample revealed a 12.9mmol/L increase in calcium content, indicative of calcite dissolution. Conversely, the WINZ-2 experiment exhibited no reaction between the injected formation water and rock samples. It was confirmed by geochemical analysis, which showed no changes compared to the base effluent analysis before the experiment.
The comparative study of oil production data from the two experiments underscores the significance of the WINZ-1 experiment. The CO2-enriched brine demonstrated a substantial increase in oil production after the breakthrough, attributed to the enhanced dissolution of CO2 into the oil and the activation of swelling mechanisms. The excess oil production occurs mostly after the breakthrough, in contrast to the WINZ-2 experiment, where oil production decreases very fast after the water reaches the producing end.
The final remaining oil saturation in WINZ-1 was 3.53 %PV lower than in WINZ-2. The analysis concludes that the CO2-enriched brine flooding resulted in an additional 3.6 %OOIP (original oil in place) oil recovery. Notably, the disparity in the extra oil produced after the breakthrough was observed to be 18.44 %OOIP in WINZ-1 compared to 8.62 %OOIP in WINZ-2. This substantial difference highlights the potential advantages of CO2 in reducing the amount of trapped oil.
Post-experiment observations revealed minor evidence of dissolution in WINZ-1, with the inlet end face of the first plug exhibiting minor pitting and a weight loss of 1.75%. However, in WINZ-2, the inlet face of the plug remained virtually unchanged; there was still a weight loss of 0.95%. This is confirmed by the visual observation of both samples. The gas permeability of the composite core in the WINZ-1 experiment increased by 6.31% due to the dissolution observed in fluid analysis. On the other hand, there was a decrease of 3.04% in the average gas permeability of composite plugs in the WINZ-2 experiment. Porosity analysis indicated a reduction of 1.41% in WINZ-1 and 1.45% in WINZ-2, primarily attributed to rock compaction during the experiment.
The overall effect that the CO2-enriched brine has on the chalk is deemed minimal and localised to the inlet of the core. The result of the μCT scanning also supports this conclusion, where the reduction in bulk volume was accompanied by an increase in bulk density, meaning that the decrease in mass was minimal. Furthermore, no change in material distribution was detectable down to the image resolution limit, i.e. no dissolution to create observable increased local porosity and no deposition to create observable increased local density. The spatial variations in chalk matrix porosity and the fossil remnant features of higher or lower density appeared identical in before- and after-state.