How do oil prices rise when crude oil inventories fall?
1) Supply and Demand. When supply falls, what supply remains becomes more valuable

2) There are massive storage tanks across the US (Cushing, Oklahoma comes to mind) where oil companies can purchase/rent storage space. Refineries cannot process crude as fast as it is extracted, so the backlog must be stored somewhere.

3) Any number of reasons. Increased consumption from industry or consumers. "unexpectedly fell" could actually mean that inventories grew slower than expected because drillers have reduced output. Perhaps a refinery came online after being shut down and helped draw down the crude stockpile.