Primary Recovery, also known as Primary Production, is the first stage in recovering oil and natural gas from the reservoirs. In this stage reservoir drives are used for recovering hydrocarbons by a number of natural mechanisms. These mechanisms include the downward displacement of the oil into a well by natural water, expansion of natural gas at the top of the reservoir, expansion of natural gas that was initially dissolved in the crude oil, and drainage using gravity that results because of the movement of oil from the upper to the lower parts of the reservoir, where the wells are placed. This difference in pressure between the reservoir and at the bottom of the well drives the hydrocarbons towards the well and to the surface. This phase produces 5-15% of hydrocarbons for the total extraction.
Companies producing oil and natural gas make efforts for reducing their spending during the initial phase of extraction from the ground. As the production continues, it leads to decrease in the pressure in the reservoir. This leads to decrease in differential pressure which leads to the use of pumps for increasing the production. Primary recovery gets over when the reservoir pressure gets too low or when the output stream consists of high amount of gas or water. The process then moves to the next stage i.e. the secondary recovery stage.