Oil-filled submarine cables are widely used for transoceanic high-voltage power transmission. These cables have a self-healing property that allows them to maintain functionality in case of minor damage by filling the gaps with insulation oil. However, this also causes oil leakage into the ocean, which poses environmental risks and requires timely detection, monitoring, and repair. In this paper, we propose a reduced-order flow simulation model for leaking oil-filled cables. This model integrates a theoretical model for the uniform flow at a distance from the leak point and a Computational Fluid Dynamics model for the non-uniform flow close to it. The experimental results confirm the effectiveness of this model for digital twin (i.e., monitor the status of leak point). The results show that the digital twin model accurately reflects the changes in the resistance of the leak point and the flow rate under different pressure conditions. The leak flow simulation model can be useful not only for oil-filled cables, but also for submarine oil and gas pipelines where sensing options other than flow rate and pressure are not available.