Geologists have understood the presence of shale gas and shale oil since the early twentieth century but always considered it unattainable due to shale’s low permeability. The shale gas revolution in the USA, brought about by the combination of horizontal drilling and hydraulic fracturing, has proven the feasibility of economically accessing this resource and significantly increasing the world’s proven reserve. As we enter the era of application of this technology worldwide, countries will have to weigh the promise of increased energy independence and hydrocarbon revenue against the potential damage to water supplies. Hydrofracking’s voracious thirst for water and potential to pollute will impact surface water bodies and aquifers. We review the basic technique, and potentially contaminating fracking fluid additives. We examine the potential damage to water quality and the potential effect on water availability in China, Mexico, South Africa, and Algeria.
Part of the book: Aquifers
A comprehensive study was carried out to understand the effects of roughness on the turbulence characteristics of flow in an open channel and would be presented in this chapter. Tests were conducted with four different types of bed surface conditions (an impermeable smooth bed, impermeable rough bed, permeable sand bed and an impermeable bed with distributed roughness) and at two different Reynolds number (Re = 47,500 and 31,000). The variables of interest include the mean velocity, turbulence intensity, Reynolds shear stress, shear stress correlation and higher-order moments. Quadrant decomposition was also used to extract the magnitude of the Reynolds shear stress from the turbulent bursting events. The effect of bed roughness on the turbulence characteristics can be seen throughout the depth of flow and thus dispute the ‘wall similarity hypothesis’. In comparison to other roughness, distributed roughness shows the greatest effect on both streamwise and vertical turbulence intensities. Velocity triple products that reflects the transportation of turbulent kinetic energy is also seen to be affected by roughness of the channel bed with a variation of 200–300% compared to the flow over smooth bed. To analyze the turbulent bursting events, quadrant decomposition tools were used and found that the roughness affected heavily in the production of extreme turbulent events. The increases of the intensity and frequency of this turbulent burst causes the increase of instantaneous Reynolds shear stress. Transport of the sediment, pollutant suspension from the channel bed, changing the composition of the nutrient in the flow, sustainability of the benthic organisms, entrainment and exchange of energy and momentum are all influenced by this change of Reynolds shear stress. The sand used to form the various bed roughness conditions is same but found that the effect on different turbulence characteristics are different for different roughness. This is a strong indication that the geometric formation of the roughness is the cause of the differences in turbulence characteristics for different roughness formed by the same sand grain.
Part of the book: Boundary Layer Flows