Maximov Denis / Shutterstock
Like coal and oil, natural gas is a fossil fuel created by the pressurized, high-temperature decomposition of organic material over millions of years.
Deposits of natural gas and oil tend to be discovered close to one another. Natural gas deposits near the surface are generally much smaller than their corresponding oil deposits. Deeper fossil fuel deposits, created at higher temperatures and under more significant pressure, tend to contain more gas than oil, with the deepest often comprising entirely of gas.
Thermogenic methane, the type of natural gas created far beneath the surface, can rise through permeable matter, like a porous stone. Geological formations, such as sedimentary basins, often trap thermogenic methane that rises.
Sedimentary basins are known to trap reservoirs of natural gas. To be able to access to these reservoirs, a well must be drilled deep enough into the ground to permit the gas to be harvested. Sedimentary basins high in natural gas are discovered all over the planet, from Saudi Arabia to Venezuela to Alaska.
Natural gas is most often extracted by drilling a singular well down into the ground. This approach is limited in the number of gas reserves it can encounter. Horizontal drilling, hydraulic fracturing, and acidizing are three additional approaches that can increase the quantity of available gas, thus raising productivity.
However, these practices (hydraulic fracturing in particular), have been associated with adverse ecological impacts. Fracking involves the cleaving of geological formations with pressurized streams of fluid that contain water, chemicals, and sand. The streams of material open the rock, enabling access to the gas deposit. This method of extraction is known to generate toxic, radioactive wastewater that, if mishandled, can contaminate groundwater. Fracking has also been associated with minor tremors, the impact of which is still being studied.
Horizontal drilling is a means of growing the size of a well without creating numerous costly and ecologically dubious drilling locations. After creating a vertical well, many systems direct the drilling horizontally.
Acidizing is a term used to describe a process of inserting acidic materials into the natural gas well, to break apart rock blocking access to natural gas.
“Unconventional” Kinds of Natural Gas
Natural gas that is cost-effective to extract and readily accessible is known as “conventional,” while natural gas that is not easy or financially-viable to obtain is known as “unconventional.”
Situated in deposits 4,500 meters or more underground, "deep natural gas" is a kind of unconventional gas. Drilling for this gas is not always financially viable, although methods to extract it have been created and are improving.
Shale gas is a different kind of unconventional natural gas deposit. Shale is a type of sedimentary stone that is extremely difficult to break down. Thick sheets of shale can hold a pocket of gas between them. Fracking and horizontal drilling are typically used to extract shale gas.
Tight gas is a type of unconventional gas deposit stuck underground due to a geological formation, making it very challenging to acquire. Accessing gas from “tight” formations generally calls for costly and challenging techniques, like fracking and acidizing.
Coalbed is often discovered alongside seams of underground coal. In the past, coal mining operations would vent coalbed gas as a waste product, but today, it is extracted for its apparent value.
Created when layers of clay quickly built up and compacted atop material was more porous, geo-pressurized zones contain natural gas pushed out of compressed clay. This gas is under extremely high pressure, and this makes it very challenging to extract. However, these zones often hold a high volume of natural gas.