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Boreholes must be sealed during many sub-surface activities connected with the energy transition, including carbon capture and storage. New and existing boreholes will need to be sealed to appropriate standards designed to prevent the leakage of stored materials. We present a simplified mechanical model of the influence of trapped brine on creep closure of a plugged borehole. The model is tested against in-situ data from the Asse Mine in Germany and related numerical models. We consider a model where brine is trapped in a borehole sealed above and below with cement plugs and the brine is expected to resist natural convergence through halite creep. The simplified model compares well to analogue data and more complex numerical models. It indicates that the time required to seal a borehole by halite creep is greater than 100 years, suggesting that legacy boreholes with trapped brine still present a leakage risk, but sealing of boreholes by creep will still be important in reducing the risk of leakage over thousands of years.