Контекст: Анализ (залежи) с точки зрения энергетических состояния и выработки.

"More free gas is produced and eventually the energy source is depleted. In some cases depending on the geology the gas may migrate to the top of the oil and form a secondary gas cap.
Some energy may be supplied by water, gas in water, or compressed rock. These are usually minor contributions with respect to hydrocarbon expansion.
By properly managing the production rates, greater benefits can be had from solution gas drives. Secondary recovery involves the injection of gas or water to maintain reservoir pressure. The gas/oil ratio and the oil production rate are stable until the reservoir pressure drops below the bubble point when critical gas saturation is reached. When the gas is exhausted, the gas/oil ratio and the oil rate drops, the reservoir pressure has been reduced and the reservoir energy exhausted."
http://en.wikipedia.org/wiki/Petroleum_reservoir

Depletion is vitally important in understanding peak oil production as well as the post-peak / postplateau production decline. The rate of production decline for individual fields of the existing production base is critical to determining global peak oil production and post-peak production decline. Decline rates for many key producing areas are, unfortunately, not well known.
Typically, in the early stages of field development, production rate increases to a maximum, reaching a peak level. Over this time period to maximum production, the physical forces within the reservoir that drive production, the reservoir’s internal energy (water drive, pressure depletion, gravity drainage, etc.) is weakened to the point where peak levels of production can no longer be sustained and the production of the field begins to decline toward an economic limit where the cost of production equals or exceeds sales. (Working Document of the NPC Global Oil and Gas Study)
http://www.npc.org/Study_Topic_Papers/15-STG-Peak-Oil-Discussions.pdf