问答题 翻译：Petroleum may be defined as a naturally occuring, complex mixture of hydrocarbons which may be either gas, liquid, or solid, depending on its own unique composition and the pressure and temperature at which it is confined.

问答题 翻译：For an oil reservoir, as pressure decreases with production, a value is reached at which a portion of the liquid vaporizes to produce a gas phase that then exists in equilibrium with liquid.

问答题 翻译：The production rate of free gas at reservoir conditions is therefore the product of the difference (R - Rs) times the surface production rate of oil times the gas formation volume factorBg.