Where does the natural energy of a reservoir come from?

1.  Liberation and expansion of solution gas

2.  Influx of aquifer water

3.  Contraction of reservoir rock skeleton

4.  Expansion of original reservoir fluids

a.  Free gas, if present

b.  Interstitial water

c.  Oil, if present

5.  Gravitational forces

Sent in by Ekwe Umahi Makolia, TalkOil9ja.