The calculated distance (air line) between Deir ez-Zor and As Safīrah is approximately 164 miles respectively 263 kilometers.
By car or train, the actual journey to As Safīrah is certainly longer, as only the direct route (as the crow flies) between Deir ez-Zor and As Safīrah has been calculated here.
Air line (approximately)
263 kilometers
142 nautical miles