What Is Primary Recovery?
Primary recovery, also known as “primary production,” is the initial stage in the extraction process for oil and gas. In crude oil production, various methods of primary recovery can be used.
Typically, the primary recovery process involves placing increased pressure on the oil within wells in order to force oil to the surface. Mechanical systems, such as rod pumps, are also sometimes used.
- Primary recovery is the first stage involved in extracting oil and gas.
- It relies on the natural difference in pressure between the surface and the underground reservoir, therefore requiring relatively limited capital investment.
- Subsequent stages in the extraction process, such as secondary and tertiary recovery, are more expensive and may be uneconomical, depending on the price of oil and gas.
How Primary Recovery Works
The key to primary recovery is the fact that the hollow well shaft drilled to access the oil is designed to have a lower pressure than the oil that is deep in the ground. This difference in pressure can be further increased by various methods, such as pumping water into the well. This method, known as a “water drive,” succeeds by displacing the oil further into the ground, increasing its pressure.
Another popular method is the so-called “gas drive,” in which the energy of expanding underground gas is used to force oil to the surface. Eventually, oil pressure can reach a point where the oil rapidly flows upwards through the well and out of the surface, creating an oil geyser.
In some cases, such as when the oil fields are especially shallow and steep, oil can drain to the surface through the sheer force of gravity.
As oil is gradually extracted from the well, the pressure underground will slowly decrease, causing the volume of oil production to decline. To mitigate against this, oil-extraction companies can use artificial lifting systems such as the rod pump to continue production. This method, known for its distinctive bobbing horse head design, employs a beam-and-crank assembly to create a reciprocating motion that uses vertical lift to pump oil out of the well using a series of plungers and valves. Eventually, the pressure underground will become so low that primary recovery will no longer be feasible, even with the use of artificial lifting systems.
Primary vs. Secondary and Tertiary Recovery
Once this point has been reached, secondary recovery techniques must be used, such as additional water injections which seek to force oil to the surface by directly applying pressure. Such an example is steam-assisted gravity drainage (SAGD), which is a secondary recovery technique used to extract heavy crude oil that is buried too deep or otherwise too burdensome to access with primary methods. Also known as the steam flooding process, SAGD uses steam generators to produce highly pressured steam that travels through pipelines into the wells. As the vapor condenses into liquid hot water, it heats the oil to make it less viscous, allowing it to flow by gravity to the bottom of the well. The oil then transfers via a pipe from the producing well at the bottom to a plant for treatment.
The final and third stage is referred to as tertiary recovery in the oil-extraction process, also known as enhanced oil recovery (EOR). This stage involves altering the properties of the oil to assist in its extraction. There are three primary methods of tertiary recovery, involving the use of heat, gas, and chemical injections, respectively. Although primary and secondary recovery techniques rely on the pressure differential between the surface and the underground well, enhanced oil recovery functions by altering the chemical composition of the oil itself in order to make it easier to extract.
Because primary recovery methods use the existing disparity in pressure between the surface and the underground reservoir in order to propel oil to the surface, it makes sense that the primary recovery stage is more economical than the secondary or enhanced stages. For this reason, oil and gas companies must calculate the estimated ultimate recovery (EUR) of a given field in order to determine whether it is profitable to extract the resources from that reservoir using a particular recovery method.