About Natural Gas
What is Natural Gas?
Natural gas is a colourless, shapeless and odourless gaseous mixture composed of simple hydrocarbon compounds, found in underground rock formations called reservoirs.
Natural gas has been used in homes since the 1st century AD in Persia following its seepage from the ground and its ignition by lightning, thus producing continuous flame that burned day and night. This makes natural gas the fuel of the past, present, and, of course, the future.
Major components of Natural Gas
Natural gas is composed mainly of methane and small amounts of other hydrocarbon gases such as ethane, propane, butane, pentane and other non-hydrocarbon impurities such as carbon dioxide, nitrogen and hydrogen sulphide.
What is the difference between Conventional and Unconventional Natural Gas?
Both conventional and unconventional gases are similar in terms of their chemical composition, mainly methane. However, the term 'unconventional’ gas refers to a source of natural gas from which the extraction relies on special or advanced production techniques and not the traditional ones. These reserves cannot be extracted through traditional techniques due to how the natural gas is deposited and the type of reserve formation. Currently, almost 28% of global gas production is sourced from these resources, so the label ‘unconventional’ does not literally reflect their status as they are quite conventional.
From the geological point of view, 'unconventional’ gas mostly describes the volume of natural gas resources that are found within the source rock where they are generated and cannot move due to extremely low permeability. On the other hand, ‘conventional’ gas migrated over a geological timeframe, from source rocks, and accumulated in permeable reservoir rock capped by a seal. Conventional gas resources are easier to extract while unconventional gas resources require special technology for extraction.
What are the major types of Unconventional Natural Gas resources?
There are four major types of unconventional natural gas resources:
Shale gas is a term used for the natural gas trapped underground in grained and porous rock deposits. As there are unfilled spaces in shale deposits with no viable connections to each other, natural gas is physically trapped and cracking is needed to release this trapped gas.
Therefore, shale gas refers to natural gas extracted from shale gas formations, whereby the shale acts as the source, reservoir, and trap for natural gas. These kinds of natural gas formations have very low porosity and permeability in the nanoDarcy range.
Shale gas is the primary and most produced gas among the unconventional types.
This type of gas is trapped in formations that are generally not permeable and porous. They are trapped in reservoirs with permeability in the milliDarcy range.
Coalbed methane (also known as CBM) is another form of unconventional natural gas that can be found in coal deposits or coal seams. This is why it is referred to as coal seam gas in some places, such as Australia.
Gas hydrates are gas molecules in the form of crystalline solids with water that looks similar to ice. These ice-like crystalline solids contain a significant volume of methane. They are formed naturally in sediments and are found on almost every continent.
How are these Unconventional Natural Gas resources extracted?
As mentioned above, unconventional gas resources are found in shale formations that are of very low permeability. Permeability is the ability of a rock formation to allow passage of fluids through it. As a result, unconventional natural gas resources require special extraction technologies. The combination of two independent technologies, namely horizontal drilling and hydraulic fracturing, makes extraction possible. Hydraulic fracturing is the process of pumping viscous fluids under high pumping pressure to overcome the underground stresses in order to create permeable pathways. The process consumes considerable amounts of water that is mixed with several chemicals, and after the hydraulic fracturing operation, the water is produced back to the surface. Environmental regulations are being taken to ensure the safe disposal of the produced fluids.
Is Hydraulic Fracturing safe?
The safety of hydraulic fracturing has sparked a debate amongst government regulators, environment groups, scientists and other technical experts. Some of the concerns centre on whether hydraulic fracturing can lead to underground water contamination, deterioration of air quality due to release of gases and chemicals, and induced seismicity.
To curb the adverse effects of the various concerns being raised, the gas industry has been working to develop innovative technologies, policies and regulation to ensure safety of people, environment and assets.