In this two-part article we will explore how is natural gas produced, before being transported via the pipeline network, as liquified natural gas (LNG) or as compressed natural gas (CNG).
Natural gas is a naturally occurring hydrocarbon gas mixture composed mainly of methane and other gases such as nitrogen, carbon dioxide and water vapour. It is used as a fuel source for transportation, heating, cooking and other industrial applications. In the context of climate change, natural gas can have immediate effects for the reduction of greenhouse gas (GHG) emissions, since its use emits between 6% and 11% less GHGs throughout the fuel life cycle and has a low-cost of switching. However, how is it produced?
For our purposes two main distinctions matter: natural gas extracted from oil and natural gas fields and biogas production.
In this first part, we will explain how natural gas is extracted from fields which have formed from decomposed animal and plant matter that existed millions of years ago. In the second part we will look at the renewable way to produce natural gas – biogas production.
First a little bit of history! Before the 20th century, natural gas had limited use – it was only used for street lighting. As a naturally occurring product in oil fields, there was no commercial use for it and without economic viability, it was either released in the atmosphere or burned in a practice called production flaring.
This started to change with the invention of the Bunsen burner and later, with the construction of pipelines for its transportation. With infrastructure to transport it, a market for natural gas was created and its adoption for cooking, heating, and manufacturing became more and more widespread. But before it reaches a gas burner or a car engine, how is it extracted?
Natural gas production begins with exploration – a cost-intensive operation, in which geologists search for deposits of natural gas at depths between 1 and 8 km.
In order to produce natural gas, first a deposit must be located. These deposits are found through geological and seismic surveys, where sound is used to create an “image” of the underground. These images are later interpreted by geologists, who identify possible locations where natural gas might be trapped.
Deposits can be of different types, but for our purposes the important distinction to remember is that there are conventional and unconventional gas resources. Conventional gas comes from deposits where standard methods are used to produce natural gas. They tend to be easier to produce and less expensive. Unconventional resources are reservoirs where there is less permeability and special techniques like hydraulic fracking must be used, in order to break loose the shale trapping the natural gas.
Having identified a reservoir, a pilot well is drilled. This well serves to give information about the properties of the reservoir, such as temperature, pressure and the natural gas found within. If the results from the pilot well are positive and there are economically viable quantities of natural gas, then a decision is taken on where to drill a production well. The decision is taken based on environmental conditions, reservoir characteristics, land rights and other local regulations.
The last step before production begins is the tightly regulated and controlled process of drilling.
While a drill head drills vertically, drilling fluid is pumped in the well. This is done for several reasons: first, it cools the drill head, removes loose earth and most importantly, keeps the pressure of the well equal to the pressure of surrounding earth. The last requirement is a must, both for the structure of the well and for environmental reasons. Since the well passes through underground aquifers, water must not escape into the well and drilling fluid must not escape into the aquifer. By keeping pressure equal, these two effects are prevented! In certain locations of the well, metal and cement casings are placed to guarantee well stability and isolation of water from the well. This is repeated as necessary, until the reservoir is reached.
Once the reservoir is reached the well releases the pressure of the reservoir and water and natural gas start flowing to the top of the well. Above ground, the water and natural gas are separated, and they travel to different processing plants for treatment, so that they can be safely used.
So, in summary, natural gas production starts with exploration in order to find possible deposits of it underground. If a deposit is found, a pilot well is drilled to find whether it is economical to produce from that reservoir. The drilling of the production well is a tightly regulated and controlled process, in order to guarantee that everything happens in an environmental and technically safe way. Lastly, once the deposit is reached, due to the pressure of the reservoir, natural gas starts flowing to the top of the well, where it is separated from the water.
Now you know the basics of how natural gas is produced. In the second part of this article, we will look at how renewable natural gas or biogas is produced.
Below you can find our sources and if you would like us to explain some part of what you read in further detail, leave us a comment below!
- Speight, James G. 2019. Natural Gas: A Basic Handbook. 2nd. Cambridge, MA: Elsevier;
- Energy Education: Conventional vs. Unconventional Resource;
- Santos GLNG: The journey of natural gas (Video);
- US Department of Energy: Alternative Fuels Data Center – Natural Gas Vehicle Emissions;
- Dyman, T.S., et al. Deep Natural Gas Resources. Natural Resources Research 12, 41–56 (2003).