A320 Captain reported an armed aircraft door was opened after arrival at gate. Maintenance was called and determined the nitrogen tank was punctured but escape slide was not deployed.

Narrative

After arriving at the gate and performing the parking checklist; the FO and I noticed that the slide indicator at door 2L was amber. Just as we observed this; we received a call from the flight attendant stating that the door handle had been accidentally opened before the door was disarmed. The flight attendant was holding the handle about halfway to prevent the slide from deploying.I instructed the flight attendant to continue holding the door handle while we contacted station operations; local maintenance; and Maintenance Control. The FO also coordinated with ground personnel to ensure the area remained clear in case of an unintended slide deployment.Once the aircraft was deplaned; maintenance arrived to assess the situation. They determined that the nitrogen tank had been punctured; but the slide had not deployed. Maintenance personnel took over holding the door handle to deplete the nitrogen tank; allowing them to safely open the door without triggering the slide.After resolving the issue; maintenance informed us that replacement parts would be needed. The situation was managed without further incident. We ensured that a maintenance write-up was completed. Additionally; we coordinated with the Chief Pilot to establish communication with the cabin crew manager and Maintenance Control.