Oil and Gas Drilling 101

While conventional oil and gas drilling (O&G) for commercial purposes has been occurring in the United States for over 150 years, recent processes utilize a variety of unconventional extraction techniques such as fracking to improve the return of hydrocarbons to the surface.

According to the U.S. Environmental Protection Agency (EPA):

Natural gas is a fossil fuel formed when layers of buried plants and animals are exposed to intense heat and pressure over thousands of years. The energy that the plants and animals originally obtained from the sun is stored in the form of carbon in natural gas. Natural gas is combusted to generate electricity, enabling this stored energy to be transformed into usable power.


As with other fossil fuels, oil is found in underground reservoirs. It is the end product of the decomposition of organic materials that have been subjected to geologic heat and pressure over millions of years.

Natural Gas

When first obtained from the ground, natural gas is composed of primarily methane with other alkanes typically mixed in, and possibly also carbon dioxide, nitrogen, and hydrogen sulfide. Shale gas, specifically, is natural gas trapped within shale geologic formations (a type of sedimentary rock).

Both oil and natural gas are considered non-renewable resources since they cannot be replenished on a human timeframe.

Current Methods of Extraction

Recently, oil and gas companies have been extracting these resources from unconventional reservoirs, such as shale formations. These “reservoirs” of gas do not connote underground lagoons; in fact, shale gas is held in tiny bubbles in the rock, and requires a combination of technologies to liberate that gas. The process typically involves directionally drilling wells, not just vertically, and often using additional techniques to “stimulate” the reservoir to increase production from the new or existing wells.

Hydraulic fracturing or “fracking” is one form of stimulation used to facilitate the production of underground resources such as oil and natural gas wells, geothermal energy, and water. Another form of well stimulation is called acidizing and will be discussed later.

For unconventional O&G drilling, the process begins with vertical drilling, and then turns horizontal (often at depths greater than 6,800 feet and below) traveling 6,300-6,400 lateral feet.

Explore this process by watching the following TED-Ed video by Mia Nacamulli, animation by Sharon Colman:

How many wells have been stimulated (e.g. fracked) in the U.S.?

This question is a common one that we receive here at FracTracker. Unfortunately, the answer is simple and not so simple at the same time.

Short Answer: No one knows – exactly.

Long Answer: We estimate that there are ~1.3 million active oil and gas facilities in the United States (map below). How many are being unconventionally drilled – utilizing technologies such as directional drilling, acidizing, or hydraulic fracturing – is a much tougher number to determine because of serious gaps in both reporting requirements and data formats. Most of these active wells are likely receiving some sort of advanced stimulation techniques, however. This article explains the topic and caveats in further detail.

If you notice an error or omission in this section, please let us know.

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