Abstract
Since time immemorial, conventional natural gas resources have not only been the easiest but also the most practical to mine. This has however been changing thanks to technological advancement. Recent times have seen an increase in the mining of the unconventional gas resources. The term unconventional may be a bit abstract. This is mainly due to the dynamic nature of the technology in which case what may be conventional today may be non-conventional tomorrow. Nevertheless, it basically means the gas whose extraction would be less economical or more difficulty mainly because the extraction technology is not fully developed. Unconventional natural gas is categorized into six groups one of which is gas-containing shales.
What is shale?
Shale refers to a sedimentary rock formed when clay-size particles of minerals and silt are compacted. Due to this composition, shale is categorized in a class of sedimentary rocks called mudstones. However, the difference between shale and other mudstones lies in the fact that it has numerous thin layers making it up and it splits readily into small thin pieces along the layers.
History
Shale was first produced in 1821 in Fredonia, New York as the pioneer commercial well for natural gas was dug in the United States. Since that time, shale in numerous other wells has generated natural gas. In the late 20th century, improved well simulation and drilling techniques were devised to be used at Barnett Shale of Texas. This enhanced the yield and natural gas recovery rate from shale. The techniques have been applied in other parts of USA resulting in increased natural gas production and leasing activity.
Importance
Certain types of hales have unique properties which make them very important resources. The Black Shales are known to incorporate an organic material which forms oil or natural gas when it breaks. Other types of shales may be crushed then blended with water to make clay used in making varied objects.
Uses
Gray and black shales are known to yield natural gas and oil. They may also contain minerals such as calcareous materials. Brown and yellow shales may produce minerals like goethite and limonite. Red shales are known to produce hematite while green shales are appropriate for production of micas and clay minerals.
What is the difference between Shale Gas and conventional gas?
The difference between conventional gas and shale gas stems from the way they are made. Conventional gas resources result from migration of natural gas to the surface of the earth. It moves from the organic-rich formation source to the reservoir rock that is highly permeable. This is where an overlying impermeable rock layer traps it. However, the shale gas deposits are formed within organic-rich shale rock. Due to shale’s low permeability, gas is inhibited from moving to other reservoir rocks that are more permeable. It is due to this arrangement that the production of shale gas would be uneconomical without hydraulic and horizontal drilling since natural gas the rates at which the natural gas flows from formation would not be sufficient to justify the expenses.
Shale plays are essentially shale formations that contain considerable natural gas accumulation and share similar geographic and geologic properties. Common shale plays include Barnett Shale play inn Texas, Fayetteville Shale, Marcellus Shale, Utica Shale and Haynesville Shale.
Where is it mined?
In late 1990’s companies that drilled natural gas came up with new methods of liberating natural gas and oil trapped within tiny shale pores. This opened up some of the most expansive deposits of natural gas in the world the first of which was Barnett Shale of Texas. With the discovery of hydraulic fracturing and horizontal drilling methods, other large fields of natural gas have been exploited including Fayetteville Shale located in Arkansas, Marcellus Shale in Appalachians and Louisiana’s Haynesville Shale. These reservoirs are said to hold natural gas sufficient to serve the needs of USA for more than two decades.
How much shale gas resources does the US hold?
More than 80 % of Natural gas used in US is produced domestically. More shale gas deposits have continued to be discovered. It is estimated that if natural gas was consumed at 22.8 Tcf a year, there would be sufficient natural gas supply to last more than a century.
What methods are used in its production?
Shale gas is produced through two main drilling techniques; hydraulic fracturing and horizontal drilling. The horizontal drilling technique provides more access to the trapped gas in the rock formation. Hydraulic fracturing involves the pumping of sand, chemicals and water to the well in order to unlock hydrocarbons that are trapped it the shale formations. In this case, it opens the fractures thereby allowing the natural gas to flow to the well.
How clean is shale gas?
One thing that you will appreciate is that shale gas is cleaner compared to oil or coal. Natural gas combustion produces considerably less pollutants such as nitrogen oxides, sulfur dioxide and carbon dioxide compared to oil and coal.
Environmental concerns in mining the gas
While natural gas production from shale deposits is quite commendable, some environmental concerns abide. Its production requires the use of large volumes of water which affects water availability for other users. It may also affect the aquatic habitats. The water produced in fracturing and drilling may also have chemicals as well as other contaminants which need to be treated before reuse. Fracturing fluid also incorporates the use of hazardous chemicals which may have negative impact on the natural habitats.
Conclusion
With more advances in technology, exploitation of shale gas is bound to go a notch higher. As much as this may draw some environmental concerns, it would be important to acknowledge that the benefits outweigh the cons not only on the economic front but also the environmental front. It is encouraging to acknowledge that quite a large amount of deposits are available and more are being discovered.
Resources
http://geology.com/gas-shales/http://geology.com/energy/shale-gas/http://geology.com/rocks/shale.shtml
