Shale gas -New Energy Resource (2)

XI'AN, China - June 16, 2013 - PRLog -- Shale Gas hiding place

Shale gas is found in shale "plays," which are shale constitutions containing significant accumulations of natural gas and which share similar geologic and geographic properties. A decade of production has come from the Barnett Shale play in Texas. Experience and information gained from developing the Barnett Shale have improved the efficiency of shale gas development around the country. Another important play is the Marcellus Shale in the eastern U.S.A.. Geophysicists and geologists identify appropriate well locations in areas with potential for economical gas output by using surface and subsurface geology techniques and seismic techniques to generated maps of the subsurface. See animated maps of production growth in the Barnett Shale and Marcellus Shale plays in Today in Energy articles - July 12, 2011  

Hydraulic fracturing (commonly called "fracking" or "fracing") is a technique in which water, chemicals, and sand are pumped into the well to unlock the hydrocarbons entrapped in shale geological formation* by unfolding cracks (fractures) in the rock and allowing natural gas to flow from the shale into the well. When used in conjunction with horizontal drilling, hydraulic fracturing enables gas producers to extract shale gas economically. Without these techniques, natural gas does not flow to the well rapidly, and commercial amounts cannot be produced from shale.

The Different between Shale Gas from Conventional Gas Production

Conventional gas reservoirs are created when natural gas migrates from an organic-rich source formation into permeable reservoir rock, where it is entrapped by an overlying layer of imperviable rock. In contrast, shale gas resources form within the organic-rich shale source rock. The low permeability of the shale greatly subdues the gas from migrating to more permeable reservoir rocks.

The Environmental Issues Associated with Shale Gas

Natural gas is cleaner-burning than coal or oil. The burning of natural gas gives off significantly lower levels of carbon dioxide (CO2) and sulfur dioxide than does the burning of coal or oil. When used in efficient combined-cycle power plants, natural gas burning can emit less than half as much CO2 as coal combustion, per unit of electrical energy output.

However, there are some potential environmental worries related with the production of shale gas. The fracturing of wells requires large amounts of water. In some areas of the country, significant use of water for shale gas production may affect the availability of water for other uses and can affect aquatic habitats.

Second, if misconducted, hydraulic fracturing liquid - which may contain potentially dangerous chemicals - can be released by spills, leakages, defective well construction, or other exposure pathways. Any such releases can pollute surrounding areas.

Third, fracturing also produces large amounts of wastewater, which may bear dissolved chemicals and other contaminants that could require treatment before disposal or reuse. Because of the quantities of water used and the complexities inherent in treating some of the wastewater elements, treatment and disposal is an crucial and challenging issue.

Finally, according to the U.S.A. Geological Survey, hydraulic fracturing "causes small earthquakes, but they are almost always too small to be a safety concern. In addition to natural gas, fracking fluids and constitution waters are came back to the surface. These wastewaters are often disposed of by injection into deep wells. The injection of wastewater into the subsurface can cause earthquakes that are large enough to be felt and may cause damage." The injection wells usually outpouring the wastewater into non-potable salt-water aquifers.