原油深藏于地下，并不呈油河的状态，而是分散于含油岩层岩石的毛细孔隙中。当钻井至油层时，分散的原油在地层原始压力的躯动下汇集起来，从采油井中喷至地表。依靠地层天然能量（自喷）采油称为一次采油。随着能量的消耗，自喷的原油逐渐减少，乃至停止。为维持地层压力，广 Crude oil is deep in the ground and does not show the shape of an oil river. Instead, it is dispersed in the capillary pores of oil-bearing rocks. When drilling to the reservoir, the dispersed crude collects under the pressure of the original formation pressure and is sprayed from the production well to the surface. Relying on the formation of natural energy (self-injection) production is called primary recovery. With the consumption of energy, self-spraying crude oil gradually reduced, or even stopped. In order to maintain the formation pressure, wide