Oil well

An oil well is a hole drilled into the Earth to bring petroleum oil to the surface. This process often also releases natural gas, known as associated petroleum gas. If a well is built to produce only gas, it is called a gas well. To create a well, crews drill down into an oil or gas reserve and may fit it with equipment like pumpjacks to extract the resources. Drilling a well is costly, starting at several hundred thousand dollars and rising significantly for hard-to-reach spots, such as offshore locations. Modern drilling began in the 1800s, but advances in rigs and technology during the 1900s made it much more efficient.

Oil and gas companies frequently buy and sell wells as assets. This is largely because a well may be unproductive when prices are low, but even a low-output well can become profitable if prices rise. New techniques, like hydraulic fracturing—injecting gas or liquid to boost oil or gas production—have also made some wells viable. However, concerns about peak oil and climate policies on fossil fuels have reduced the number of wells and expensive methods that make economic sense.

Neglected or poorly maintained wellheads create environmental problems. They can leak methane or other toxic substances into the air, water, and soil. This pollution gets worse when wells are abandoned or orphaned—meaning they are no longer economically viable and their former owners stop maintaining them. A 2020 estimate from Reuters indicated there were at least 29 million abandoned wells worldwide, which are a major source of greenhouse gas emissions that worsen climate change.

**History**

The earliest known oil wells were drilled in China in 347 CE, reaching depths of about 240 meters using bits attached to bamboo poles. The oil was burned to evaporate brine for salt production. By the 10th century, extensive bamboo pipelines connected these wells to salt springs. Ancient records from China and Japan mention using natural gas for lighting and heating, and in 7th-century Japan, petroleum was called "burning water."

According to Kasem Ajram, the Persian alchemist Muhammad ibn Zakarīya Rāzi (Rhazes) distilled petroleum in the 9th century, producing chemicals like kerosene in an alembic, mainly for lamps. Arab and Persian chemists also distilled crude oil to make flammable products for military use. Through Islamic Spain, distillation reached Western Europe by the 1100s.

Some sources say that from the 9th century, oil fields near modern Baku, Azerbaijan, were exploited for naphtha. Marco Polo described these in the 13th century, noting that the output filled hundreds of shiploads. Visiting Baku in 1264, he saw oil collected from seeps and wrote of a fountain producing oil in such abundance that a hundred shiploads could be taken at once.

In 1846, the first well drilled with percussion tools for oil exploration reached 21 meters deep at Bibi-Heybat, near Baku. Between 1846 and 1848, the first modern oil wells were drilled on the Absheron Peninsula northeast of Baku by Russian engineer Vasily Semyonov, applying ideas from Nikolay Voskoboynikov. Polish pharmacist Ignacy Łukasiewicz drilled one of the world's first modern oil wells in 1854 in the Polish village of Bóbrka, and built one of the first oil refineries in 1856.

In North America, the first commercial oil well began operation in Oil Springs, Ontario, in 1858, while the first offshore oil well was drilled in 1896 in the Summerland Oil Field on the California coast. Early modern wells were drilled percussively, repeatedly raising and dropping a bit on a cable. In the 20th century, cable tools were largely replaced by rotary drilling, which could reach much greater depths more quickly. The record-depth Kola Borehole used a mud motor to reach over 12,000 meters.

Until the 1970s, most oil wells were essentially vertical, though lithological variations caused slight deviations. Modern directional drilling allows for highly deviated wells that can become horizontal. This is valuable because reservoir rocks are usually horizontal; a horizontal wellbore has more surface area in the production zone than a vertical one, leading to higher production rates. Deviated and horizontal drilling also enables reaching reservoirs several kilometers away from the drilling site, allowing production from beneath locations that are difficult to access, environmentally sensitive, or populated.

**Life of a Well**

**Planning**

For a production well, the target is chosen to optimize production and manage reservoir drainage. For an exploration or appraisal well, the target is selected to confirm a viable hydrocarbon reservoir or learn its extent. For an injection well, the target is chosen to place the injection point in a permeable zone that can support disposing of water or gas and/or pushing hydrocarbons.