How do oil wells work?
Oil wells work by drilling deep into the Earth to create a pathway that allows underground petroleum oil and often associated natural gas to be brought up to the surface.
An oil well is fundamentally a drillhole boring into the Earth. As stated in the reference, it is designed to bring petroleum oil hydrocarbons to the surface. These hydrocarbons, which include crude oil and natural gas, are trapped in porous rock formations underground. The well acts as a conduit to extract these valuable resources.
Often, usually some natural gas is released as associated petroleum gas along with the oil. In cases where a well is specifically created to extract only gas, it may be referred to differently; the reference notes that a well that is designed to produce only gas may be termed a gas well.
Stages of an Oil Well
Creating and operating an oil well involves several key stages:
- Drilling: A specialized drilling rig uses a drill bit to bore through various layers of rock down to the reservoir containing oil and gas. Sections of pipe, called casing, are inserted into the hole and cemented into place to prevent the wellbore from collapsing and to isolate different underground zones.
- Completion: Once the drilling reaches the reservoir, the well must be "completed." This involves perforating the casing in the reservoir zone to allow oil and gas to flow into the wellbore. Tubing is then run inside the casing to transport the fluids to the surface, and various valves and equipment (like a "Christmas tree" assembly) are installed at the wellhead to control the flow.
- Production: This is the operational phase where oil and gas are extracted from the well. The method of extraction depends on the characteristics of the reservoir.
How Oil and Gas Come Up
The force that brings oil and gas to the surface can vary:
- Natural Pressure (Primary Recovery): In some reservoirs, the pressure is high enough from compressed gas, water drive, or rock expansion to push the oil and gas up the wellbore naturally.
- Artificial Lift: As reservoir pressure declines, mechanical assistance is often needed. This can involve:
- Pumps: Like the familiar nodding beam pumps (pumpjacks) seen in many oil fields.
- Gas Lift: Injecting gas into the wellbore to lighten the fluid column and allow it to rise.
- Electric Submersible Pumps (ESPs): Pumps placed at the bottom of the well.
- Enhanced Oil Recovery (EOR): To extract more oil after natural pressure and artificial lift are no longer sufficient, methods like injecting water, gas, or chemicals into the reservoir are used to push the oil towards the wellbore.
Associated Gas
As mentioned, natural gas is usually released as associated petroleum gas along with the oil. This gas is often separated from the oil at the surface and can be processed and sold, used on-site for power or injection, or sometimes flared (burned) if there are no facilities to handle it. Wells designed only for gas extraction are simply called gas wells.
Oil Wells vs. Gas Wells
While the basic drilling concept is similar, the target and production methods can differ slightly.
| Feature | Oil Well | Gas Well |
|---|---|---|
| Primary Target | Petroleum oil hydrocarbons | Natural gas |
| Associated Output | Usually releases natural gas along with oil | May produce some liquid hydrocarbons (condensate) |
| Purpose | Designed to bring petroleum oil hydrocarbons to the surface | Designed to produce only gas (as per reference) |
| Fluid Type | Liquid (oil) with dissolved or associated gas | Primarily gas |
In essence, oil wells are engineering marvels that provide the vital link between deeply buried hydrocarbon reserves and the surface infrastructure needed to process and utilize them.
