What are natural gas shale deposits, and where do they come from? Conventionally, natural gas is found in pockets beneath layers of impermeable rock, either as associated gas (gas that shares the pocket with liquid oil) or non-associated gas (gas that is in the pocket on its own). Shale gas, on the other hand, is natural gas that is found in layers of shale. Instead of being held in large pockets, shale gas is typically spread throughout the shale in smaller bubbles.
This type of gas is usually also deeper beneath the Earth’s surface than conventional pockets of natural gas. Because of this, it is more difficult to extract than conventional gas. Yet, processes such as horizontal drilling and hydraulic fracturing (fracking) have made it economically viable to acquire natural gas from shale deposits. Currently, the United States, Canada, and China are the countries that make the largest use of natural gas shale deposits.
Formation of Natural Gas Shale Deposits
Most natural gas was formed in the Devonian Period, 300-400 million years ago. Organic material from aquatic plants and animals were trapped in sand at the bottom of oceans or lakes. This material was converted to natural gas (mostly methane) as the sediment around it was converted to types of rock, such as sandstone and shale.
Natural gas that was formed in more permeable types of rock, such as sandstone, was able to move through the rock and collect in pockets of what is now known as conventional natural gas. Shale, on the other hand, is impermeable. Therefore, natural gas that was formed in shale could not move through the rock. It is therefore more evenly distributed throughout the shale. The largest known shale deposits of shale gas are in China (1114 trillion cubic feet), Argentina (802 trillion cubic feet), Algeria (707 trillion cubic feet), the United States (665 trillion cubic feet), and Canada (573 trillion cubic feet).
History of Natural Gas Extraction from Shale Deposits
Since extraction of conventional natural gas is easier than extraction of shale gas, the exploitation of shale gas deposits only began to increase as conventional natural gas supplies decreased. Shale gas was extracted at a small scale as early as 1821, and the techniques that enabled more efficient extraction of shale gas—horizontal drilling and hydraulic fracturing—were developed in 1930 and 1947, respectively.
Large-scale extraction of shale gas, however, has increased dramatically in the past twenty years. In 2000, only 1% of the United States’ natural gas production came from shale gas, in 2010 that figure had risen to 20%, and by 2035, it is estimated that 46% of the United States’ natural gas will come from shale. China, the country with the largest shale gas deposits, built its first shale gas well in 2011. By 2014, China had 200 shale gas wells.
Economics of Natural Gas Shale
Extraction of natural gas shale is achieved by drilling down to a shale layer. The aim is to drill one with a lot of organic material that has become gas. Since the gas is distributed throughout the shale, more gas is acquired if the well encounters a larger area of shale. This is where horizontal drilling and hydraulic fracturing come in. Layers of shale tend to be horizontal rather than vertical. Therefore, drilling horizontally along a shale layer allows a well to encounter more of the rock and therefore more of the gas. In a similar vein, hydraulic fracturing uses a liquid (such as water) at high pressure to break apart the shale and release more natural gas into the well. The pressurized liquid used in hydraulic fracturing also contains proppants (such as sand) that serve to hold open fractures created by the liquid.
Before the full development of large-scale horizontal drilling and hydraulic fracturing, extraction of shale gas was not economically viable. In the United States, for example, shale gas extraction was only made possible through government subsidies. However, in 1998, the company Mitchell Energy implemented slick-water fracturing more efficiently and on a larger scale than previously achieved, and revolutionized shale gas extraction on their property over the Barnett Shale in Texas.
Environmental Impacts
One of the largest objections to extraction of gas from natural gas shale deposits is that the techniques used. This is true especially for hydraulic fracturing (fracking) since it’s harmful to the environment and to nearby humans. For example, chemicals used in drilling and fracking can leak into water.
A major concern about fracking is the possibility of earthquakes being caused. In the process of fracking, microseismic events are common. As of August 2016, nine earthquakes that can be felt by humans have been recorded in association with fracking. However, a much larger cause of earthquakes is the wells dug to dispose of wastewater from activities such as fracking.
Extraction from shale deposits has been found to release more greenhouse gases than conventional natural gas, but much less than coal mining. Finally, fracking for shale gas causes noise pollution and can thus have a negative effect on people who live nearby.
Future of Natural Gas Shale
Given the recent rise of extraction of natural gas from shale deposits, much legislation about shale gas extraction is still in formation. Because of the positive economic effects and negative environmental effects of shale gas extraction, different countries are coming to different conclusions for how to proceed. Some countries, such as China and Poland, have plans underway to greatly ramp up production of natural gas from shale deposits. Other countries are less enthusiastic. Hydraulic fracturing is banned in France. In Germany, there is a moratorium on shale gas extraction, pending further research.
In many countries, the greatest concern about implementing fracking is potential damage to the water supply. The full extent of shale gas resources and the scope of environmental impacts of extraction are still in the process of being researched in most of the world. Natural gas shale deposits may be one good means of extending the world’s supply of fossil fuels. However, the ambiguity of benefits and costs makes the future uncertain.