How Is Oil and Gas Produced Once It’s Found?
The challenge always facing production engineers is how to obtain the most oil and gas possible from the rocks beneath the earth’s surface. Remember, hydrocarbons reside within the pore spaces of rocks, but not all rocks allow oil and gas to move freely. In such cases, advanced techniques are needed to move oil and gas from the rocks to the wellhead. According to the Society of Petroleum Engineers, up to two-thirds of the hydrocarbons in some fields with may not be recoverable, due to the difficulty of extracting oil and gas in some geologic conditions.
To begin production, a well must first be “cased,” or lined with pipes cemented into place, to prevent contamination of ocean and/or subsurface water. Next, a small diameter tubing string kept in place with packers is installed, through which the hydrocarbons ultimately reach the surface. Hydrocarbons are often locked underground at high pressures; therefore valves and other equipment at the wellhead are needed to regulate pressure and flow rates.
Natural underground pressure is often enough to push oil and gas to the surface during the earlier states of production. Some fields produce from natural pressure for many years, and even decades. However, mechanical or artificial “lift” pumping devices are ultimately needed to bring fields to their full production capacity. Onshore, the “horsehead” pumps seen around many oil fields are a form of artificial lift, although many more types of artificial lift systems have since been developed.
Oil and gas wells naturally decline in production rates over time. For this reason, the industry is constantly developing and improving methods to stem the declines. One common method is known as a well “workover,” or a thorough cleaning of the wellbore to enable oil and gas to move more freely. Another so-called “frac” process involves fracturing rocks to provide a better pathway for the hydrocarbons.
As fields age, however, more aggressive measures are often warranted. These include waterflooding, where water, often the large amounts that are produce in conjunction with oil and gas, is injected back into the reservoir to help push oil out of the pores in rocks. More advanced methods, called Enhanced Oil Recovery (EOR) are also increasingly used today. EOR generally involves re-injecting either steam or other substances, such as carbon dioxide, nitrogen or a soapy mixture back through the well and into the reservoir to help flush out additional oil and gas.
In any event, oil and gas must be moved from the production area to gas processing facilities or oil refineries. Both onshore and offshore, this is generally done through spur pipelines from the field that connect to larger ones – and natural gas, of course, must be moved via pipeline. More options exist with oil, such as storing it in a tank, then moving it by truck, ship or barge.