Lee, you can get EIA historical consumption data and methodology from the link below. They have 17 years of weekly storage report data accessible from a spreadsheet (the link to that is embedded in the report). The weekly data from year to year doesn't overlap precicely due to changes in the date of each Friday from year to year, but one can estimate fairly closely the average consumption of each week from the database within a few days. For example, the seasonal average injection for this upcoming Friday is 77.5 Bcf (19 years of data). The average 5 year injection is 77.8 Bcf.
Cheers.