Cavern formation

The story does not end with cavern formation. Many limestone caves, such as Carlsbad Caverns, contain spectacuiar formations that inciude staiagmites, stalactites, and limestone columns. We need to examine the equiiibria more cioseiy to understand how these structures form. 

The reaction between acids and bases is also responsible for some of the most spectacular, breathtaking cavern formations on Earth. As rainwater falls through the air, it encounters carbon dioxide (C02) gas. As it moves through the ground, the rainwater comes into contact with even more carbon dioxide from decaying plants and animals. Eventually, some portion of the rainwater reacts with the carbon dioxide it comes into contact with to form a weak carbonic acid ... 

Cavern formation, shown in Figure 9.8, is very real and highly undesirable. It can be avoided by better distribution of the shear stress (using multiple impellers), thus creating lower local effective viscosity and higher circulation rates throughout the vessel. 

There are other applications in which a high concentration (> hy volume) of small size solids produces a solid-liquid mixture with non-Newtonian yield stress characteristics leading to cavern formation (see Figure 1.10 and equation 15.8) when agitated. ... 

Cavern Formation and Size in Yield Stress Fluids... 

Figure 18-13 Cavern formation in shear thinning fluids. A well-mixed region exists in regions of high shear rate, while stagnant regions form in regions of low shear rate.

The demand for gas is highly seasonal. Thus pipeline companies economi2e by si2ing production faciUties to accommodate less than the system s maximum wintertime demand. Underground storage faciUties are used to meet seasonal and daily demand peaks. In North America, gas is stored in three main types of underground formations depleted oil or gas fields, aquifers that originally contained water, and caverns formed by salt domes or mines. 

Deep-Well Injection Deep-well injection for the disposal of liquid wastes involves injecting the wastes deep in the ground into permeable rock formation (typically limestone or dolomite) or underground caverns. 

The types of aqueous equilibria described in this section have been given special names, and it is essential that you be able to recognize them. Keep in mind, however, that the principles described in the previous sections apply to all chemical equilibria. Chemists categorize equilibria for convenience, but they treat all equilibria the same way. Our Chemistry and the Environment Box explores the roles of these equilibria in a spectacular natural process, the formation of limestone caverns. 

Limestone caverns are among nature s most spectacular displays. These caves occur in many parts of the world. Examples are Carlsbad Caverns In New Mexico, Jeita Caves in Lebanon, the Blue Grotto in Italy, and the Jenolan Caves In Australia. Wherever they occur, the chemistry of their formation involves the aqueous equilibria of limestone, which Is calcium carbonate. Three such equilibria, linked to one another by Le Chatelier s principle, play essential roles In cave dynamics. 

A resin is injected in the formation, which cures irreversibly suitable for bigger caverns. 

The main problem of hydrate formation will arise in pipelines transporting natural gas, because gas hydrates are solids and will leave deposits. The solid deposits reduce the effective diameter of the pipeline and can therefore restrict or even clog the flow properties. Furthermore, the formation of condensates, hydrates, or ice may occur in the course of decompression of natural gas stored in natural reservoirs (e.g., in salt caverns). The operation of oil and gas pipelines in the deep sea is significantly complicated by the formation of gas hydrates [1204]. Experience indicates that large gas hydrate plugs in gas and oil pipelines form most actively during the period of an unforeseen long shut-down. In static conditions, three types of hydrate crystals can be formed [1153] ... 

Figure 7.1 Cave formations are caused when rainwater and carbon dioxide mix and form a weak carbonic acid, which then dissolves the calcium carbonate of limestone beneath the earth, allowing for cave formation. The photo shows stalactites and stalagmites and other formations at Luray Caverns in Virginia.

Injection pump. An injection pump is used to force the waste into the injection zone, although in very porous formations, such as cavernous limestone, the hydrostatic pressure of the waste column in the well is sufficient. The type of pump is determined primarily by the well-head pressures required, the volume of liquid to be injected, and the corrosiveness of the waste. Single-stage centrifugal pumps are used in systems that require well-head pressures up to about 10.5 kg/cm2 (150 psi), and multiplex piston pumps are used to achieve higher injection pressures. 

The wastes are injected into the lower part of the carbonate Floridan aquifer, which is extremely permeable and cavernous. The natural direction of groundwater flow is to the southeast. The confining layer is 45 m (150 ft) of dense carbonate rocks. The chloride concentration in the upper part of the injection zone is 1650 mg/L, increasing to 15,800 mg/L near the bottom of the formation.172 The sources used for this case study did not provide any data on the current injection zone. The native fluid was basically a sodium-chloride solution but also included significant quantities of sulfate (1500 mg/L), magnesium (625 mg/L), and calcium (477 mg/L). 

There are two types of caverns used for storing liquids. Hard rock (mined) caverns are constructed by mining rock formations such as shale, granite, limestone, and many other types of rock. Solution-mined caverns are constructed by dissolution processes, i.e., solution mining or leaching a mineral deposit, most often salt (sodium chloride). The salt deposit may take the form of a massive salt dome or thinner layers of bedded salt that are stratified between layers of rock. Hard rock and solution-mined caverns have been constructed in the United States and many other parts of the world. 

Since salt caverns contain brine and other contaminants, the type of gas to be stored should not be sensitive to the presence of contaminants. If the gas is determined suitable for cavern storage, then cavern storage may not offer only economic benefits and enhanced safety and security salt caverns also offer relatively high rates of deliverability compared to reservoir and aquifer storage fields. Solution-mined gas storage caverns in salt formations operate as uncompensated storage—no fluid is injected into the well to displace the compressed gas. 

Frequently, hydrates become important in natural gas storage in salt caverns for peak shaving, or seasonal or diurnal volume averaging delivery of gases. The work by deRoo et al. (1983) discusses this process, regarding hydrate formation in high salt concentration, with their data provided in Chapter 6 on methane hydrate inhibited by sodium chloride. 

The most common type of damage found was that of irregularly shaped caverns (Fig. 12.89) (up to 1 pm in diameter). However, these formations began in island stmctures that eventually spread (over 2-3 weeks for rj =-1.0 and T = 300 °K) over most of the electrode to 1 pm in depth. 

Solution caverns or caves often contain deposits of recrystallized calcium carbonate, usually in the form of the mineral aragonite. Stalactites, stalagmites, and other cave formations are called speleothems. Created gradually by the precipitation of aragonite from groundwater, many speleothems display a layered structure. Recent study shows that bacteria and other simple life forms may contribute to the formation of cave deposits. 

Calculate the amount of calcite being dissolved every year in an area of 50 km 30 km. How large is the volume of cavities created by this kind of karst weathering assuming a density of calcite of 2.6 g/cm3 How much is the theoretical subsidence resulting from the calcite dissolution per year over the whole area of 50 km 30 km (Formation of caverns first prevents an immediate subsidence. Only after those caverns collapse, site specific subsidence structures appear at the surface. This aspect of time and spatial distribution shall be neglected for the calculations above.)... 

Dissolution, precipitation, and deposition processes (e.g., those present during the formation of limestone caverns or in the formation of brines or high-salinity waters). 

This process and its reverse account for the formation of limestone caves and the stalactites and stalagmites found there. The acidic water (containing carbon dioxide) dissolves the underground limestone deposits, thereby forming a cavern. As the water drips from the ceiling of the cave, the carbon dioxide if ->st... 

For stationary hydrogen storage on a large scale, underground caverns or cavities are an appealing option, often offering storage solutions at a very low cost. Three possibilities of interest are salt dome intrusions, cavities in solid rock formations and aquifer bends. 

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