hydraulic fracturing is used to increase the rate at which fluids, such as petroleum, water, or natural gas can be recovered from subterranean natural reservoirs. reservoirs are typically porous sandstones, limestones or dolomite rocks, but also include "unconventional reservoirs" such as shale rock or coal beds. hydraulic fracturing enables the extraction of natural gas and oil from rock formations deep below the earth's surface (generally ), which is greatly below typical groundwater reservoir levels. at such depth, there may be insufficient permeability or reservoir pressure to allow natural gas and oil to flow from the rock into the wellbore at high economic return. thus, creating conductive fractures in the rock is instrumental in extraction from naturally impermeable shale reservoirs. permeability is measured in the microdarcy to nanodarcy range. fractures are a conductive path connecting a larger volume of reservoir to the well. so-called "super fracking," creates cracks deeper in the rock formation to release more oil and gas, and increases efficiency. the yield for typical shale bores generally falls off after the first year or two, but the peak producing life of a well can be extended to several decades.