Acid-rock reactions, rate

Acid fracturing, friction reducers, 15 Acid hydrolysis, lignin, 173 Acid injection into carbonate reservoir, 610-611 Acid-rock reactions, rate, 15,16 Add wormholing in carbonate reservoirs, 608-620 in carbonate rocks, 610-611 Acidity-controlled redox reactions, 141-142 Addization... 

So-called "wormholes" can be formed when the injected acid primarily enters the largest diameter flow channels in carbonate rock further widening them (107). Acid only invades the small flow channels a short distance greatly reducing treatment effectiveness. High fluid loss rates, low injection rates, and reduced rates of acid-rock reactions decrease the wormhole length. 

Yet, controlled studies of weathering promise the generation of data usable,not only for the determination of weathering rates> but also for the reconstruction of the history of the acidity of precipitation. As shown earlier in the introduction, the absence of nitrates and sulfates in the weathered rock indicates that GO is the cause of decay this reveals that the pH of the precipitation has been nearly 5.6. Since the presence of NO2 and SO2 considerably reduce the pH of the precipitation, the occurrence, quantities, and the depth to which the weathered products have penetrated in dated stones (e.g. monuments in graveyards) may form bases for determinations ofactual acidity when the pH of the precipitation is below 5.6. It will, however, be necessary to determine the reaction rates in laboratory conditions at known acidity levels and correlate them with reaction rates in ambient conditions,both for stones which are directly exposed to precipitation and those which weather due to acid aerosols while protected under the dome. 

Hydrochloric acid is commonly used to stimulate carbonate (calcite and dolomite) reservoirs [J]. The reaction rate of HCl acid with calcite is very fast [43, 44], In conventional stimulation when 15 wt% HCl is used at low flow rates, the acid reacts with carbonate rocks and causes a face... 

The reaction rate of regular HCl with calcite is fast. However, mass transfer by diffusion plays a significant role in the case of the emulsified acid. As the temperature is increased, the viscosity of the emulsified acid decreases. Also, the probability that an acid drop will contact the calcite rock increases. Both factors enhance mass transfer of the acid to the rock surface. This point was examined by Al-Anazi et al. [14] who showed that the dissolution rate of the emulsified acid increases at high temperatures (Figure 7). 

The geochemical computer models, EQ3/6 (Wolery 1978), SOLMINEQ.88 (Kharaka et al. 1988), PATHARC.94 (Perkins and Gtmter 1995) and TOUGHREACT (Xu et al. 2000, 2004) have been used to model water-rock reactions driven by the formation of carbonic acid when waste CO2 is injected into deep aquifers using experimentally determined rate data (e.g., Gunter and Perkins 1993). These calculations have shown that carbonate aquifers are limited in the quantity of CO2 that can be trapped, while siliciclastic aquifers have superior potential for trapping CO2 through the precipitation of carbonates, particularly,... 

The aqueous chemistry of iron is also important in a number of other settings. Iron can be the dominant cation released in acid rock drainage, due to the oxidation of pyrite (FeS2(s)) when it becomes exposed to air and water. This process is catalysed by bacteria which cycle ferrous iron back to ferric iron which, in turn, can oxidise further pyrite. Thus, the rate of oxidation will depend on the aqueous concentration of ferric iron. If insufficient iron (and acid) is produced or the iron is removed by the inherent neutralisation capacity of the material, the rate of oxidation will be substantially reduced. The precipitation of iron oxyhydroxide phases and their ability to adsorb other aqueous elements have also been studied in detail (Dzombak and Morel, 1990). The removal of arsenic from drinking water by hydrous iron oxides is one example of these adsorption reactions. 

Mechanistic details of carbonate-rock deterioration in polluted environments are needed to protect and refurbish structures and monuments at risk to acid rain and air pollution. For example, if diffusion of reaction products away from the rock surface is limiting the rate of dissolution, then modeling rock deterioration, using simple chemical models, will be difficult. 

Equator for a time.3 This would have meant that all the land masses on Earth were free of ice. To understand why this should matter, we must look at what happens when rock is exposed to the air, or to warm oceans with plentiful carbon dioxide. Rock can be eroded by dissolved carbon dioxide, which is weakly acidic. As a result of this reaction, carbon dioxide is lost from the air and becomes petrified in carbonates. But when glaciers form over land, the underlying rock becomes insulated from the air by the thick layer of ice. This means that the rate of rock erosion by carbon dioxide is cut to a fraction and the carbon dioxide stays in the air. In fact, in such a situation, carbon dioxide actually builds up in the air, because it is also emitted more or less continuously from active volcanoes. 

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