This dissertation examines how the analysis of Supply Chain flows can support the structuring and performance improvement of a complex and decentralised logistics system. The study is based on a six-month consulting mission conducted within Talan for GRDF, the main natural gas distribution operator in France, in the context of a national Material Supply Chain transformation project. Operating a critical infrastructure under strong regulatory and operational constraints, GRDF relies on a Supply Chain that directly conditions field intervention reliability and service continuity. Historically developed through decentralised regional practices, the Material Supply Chain progressively evolved into a heterogeneous system characterised by multiple ordering and delivery channels, fragmented information flows and limited consolidated visibility at national level.