The natural gas transmission system conducts sales-quality natural gas from the
producers (i.e., from gas batteries, gas processing plants and imports at the border) to
market (i.e., gas distribution systems, the border for export, and direct sales to end
Large straddle plants may exist on some gas transmission pipeline systems. Straddle
plants feature a high-capacity cryogenic deep-cut liquid extraction process designed to
remove any residual ethane and heavier hydrocarbons left in the gas by the upstream gas
processing plants. Although located on the gas transmission system, straddle plants are
evaluated under gas processing and production.
The storage facilities accommodate fluctuating differences between gas supply and
demand rates. These facilities usually feature an underground cavern with multiple wells
for injection/removal of the gas. In addition, they include compressors to recompress
stored gas when it is removed from the cavern, and dehydration facilities for removal of
any moisture the gas may have picked up in the cavern.
Some storage facilities may store natural gas in a liquefied state in spherical vessels.
These types of storage facilities are normally located near the start of gas distribution
systems. They feature a liquefaction plant at the inlet to the storage vessels and a
vapourizer and compression at the outlet to the vessels.