Waste-reservoir interactions

Processes Significant in Different Types of Waste-Reservoir Interactions... 

Backflushing of injected wastes can also be a good way to observe waste/reservoir geochemical interactions. Injected wastes are allowed to backflow (if formation pressure is above the elevation of the wellhead) or are pumped to the surface. Backflowed wastes are sampled periodically (and reinjected when the test is completed) the last sample taken will have had the longest residence time in the injection zone. Keely165 and Keely and Wolf166 describe this technique for characterizing... 

Chemical reactions may result from interactions among and between the three phases of matter solid, liquid, and gas. The major interactions that occur in the deep-well environment are those between different liquids (injected waste with reservoir fluids) and those between liquids and solids (injected wastes and reservoir fluids with reservoir rock). Although gases may exist, they are usually dissolved in liquid at normal deep-well pressures. 

Each interaction involves numerous chemical processes. The dominance of a specific interaction depends on the type of waste, the characteristics of the brine and rock in the reservoir, and environmental conditions. Table 20.14 describes some of the more common processes that may result in incompatibility. 

The geochemical interactions possible between an injected waste and the reservoir rock and its associated fluids can be quite complex. Thus a combination of computer modeling, laboratory experimentation, and field observation will inevitably be necessary to satisfy current regulatory requirements for a geochemical no-migration deep-well injection. This section covers the computer methods and models available for predicting geochemical fate. 

Field studies are an important complement to geochemical modeling and to laboratory studies. The following are two ways to investigate the interactions between injected wastes and reservoir material ... 

A representative scheme of a low pressure FCS plant for automotive application is shown in Fig. 4.9. The reactant supply sub-systems could directly interact with thermal and water management sub-systems, by means of a simultaneous transfer of heat and mass into the humidifier devices, which should be inserted at the entrance of the stack for both reactants. Thermal sub-system includes an internal coolant circuit that is essentially constituted by a liquid pump, a radiator necessary to reject the stack waste heat, and a liquid reservoir. Other minor but equally important components are the de-ionizer filters, thermostat, and valves. 

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