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Cavern definition: The definition of a cavern is a large cave. (noun) An example of a cavern is Mammoth Cave in Kentucky.
Saeid Mokhatab. Mak, in, 2019 1.13.3 Salt CavernsSalt caverns are formed out of existing salt bed deposits. Most of the large salt caverns are located in the salt domes along the Gulf Coast in the US. Salt caverns in Northeastern, Midwestern, and Western States are also available but the applications are limited by the lack of suitable geology.The cavern is man-made by drilling a well down into the formation, and pumping water through the completed well to dissolve the salt which returns to the surface as brine. The walls of the cavern are very resilient against reservoir degradation.As the salt cavern is an open vessel, it offers very high deliverability.
Flow rates can be high and they can be brought on stream and ramped to full flow quickly. They are best for peak loads and short term trading rather than long term seasonal storage. Peak load can be provided by salt caverns, where the deliverability is higher, turnovers will be higher and facilities are smaller. Salt caverns turnover can be daily or weekly, entirely dictated by commercial trading. ParameterStepCavern excavationComments123451st2nd3rdMaximum principal stress (MPa)9.2911.499.918.398.378.568.718.83Maximum displacement (mm)Total deformation along horizontal jointsTotal1.851.802.636.998.168.288.438.65Wall–––1.333.783.883.923.97Crown (vertical component)0.501.082.624.054.334.394.877.01Maximum shear displacement (mm)Along horizontal joint1.111.542.493.514.675.675.545.56Crown1.111.542.493.513.703.704.106.85Maximum hydraulic aperture (mm)-crown0.691.011.622.642.863.683.724.13Maximum axial forces on bolts (tnf)7.52525.
After the second excavation step, there is a progressive increase in displacement and the maximum deformation occurs along the sub-horizontal fractures on the right- and left-hand sides of the cavern. In the crown of the cavern, the maximum calculated deformation calculated after the 5th excavation sequence is 4.3 mm ( Table 12.2).
This value continues to increase after each postal cavern is excavated and the final deformation vectors after the completion of excavation are shown in Fig. Notice the tendency for horizontal displacements of the blocks on each side of the crown of the cavern. The maximum shear displacement along the horizontal fractures on the crown after the 5th excavation sequence is about 4 mm and increases to almost 7 mm after the excavation of the third postal service cavern. Calculated maximum hydraulic aperture and axial force on rock bolts are also presented in Table 12.2. Speight Ph.D., D.Sc., in, 2019 5.4.3 Salt cavernsEssentially, salt caverns are formed out of existing salt deposits.
These underground salt deposits may exist in two possible forms: salt domes and salt beds. Salt domes are thick formations created from natural salt deposits that, over time, leach up through overlying sedimentary layers to form large dome-type structures. They can be as large as a mile in diameter, and 30,000 ft in height. Typically, salt domes used for natural gas storage are between 6000 and 1500 ft beneath the surface, although in certain circumstances they can come much closer to the surface.
Salt beds are shallower, thinner formations. These formations are usually no more than 1000 ft in height. Because salt beds are wide, thin formations, once a salt cavern is introduced, they are more prone to deterioration, and may also be more expensive to develop than salt domes.Once a suitable salt dome or salt bed deposit is discovered, and deemed suitable for natural gas storage, it is necessary to develop a “salt cavern” within the formation. Essentially, this consists of using water to dissolve and extract a certain amount of salt from the deposit, leaving a large empty space in the formation. This is done by drilling a well down into the formation and cycling large amounts of water through the completed well. This water will dissolve some of the salt in the deposit, and be cycled back up the well, leaving a large empty space that the salt used to occupy—this process is known as “salt cavern leaching.” Some of the salt is dissolved leaving a void and the water, now saline, is pumped back to the surface.
The process continues until the cavern is the desired size. Once created, a salt cavern offers an underground natural gas storage vessel with very high deliverability.Salt cavern leaching is used to create caverns in both types of salt deposits and can be quite expensive. However, once created, a salt cavern offers an underground natural gas storage vessel with very high deliverability. In addition, cushion gas requirements are the lowest of all three storage types, with salt caverns only requiring about 33% of total gas capacity to be used as cushion gas.These underground salt caverns offer another option for natural gas storage. These formations are well suited to natural gas storage in that salt caverns, once formed, allow little injected natural gas to escape from the formation unless specifically extracted. The walls of a salt cavern also have the structural strength of steel, which makes it very resilient against degradation over the life of the storage facility. Salt caverns allow very little of the injected natural gas to escape from storage unless specifically extracted.
The walls of a salt cavern are strong and impervious to gas over the lifespan of the storage facility.Salt cavern storage facilities are primarily located along the Gulf Coast, as well as in the northern states, and are best suited for peak load storage. Salt caverns are typically much smaller than depleted gas reservoirs and aquifers, in fact underground salt caverns usually take up only one-hundredth of the acreage taken up by a depleted gas reservoir.
As such, salt caverns cannot hold the volume of gas necessary to meet base load storage requirements. However, deliverability from salt caverns is typically much higher than for either aquifers or depleted reservoirs. Therefore natural gas stored in a salt cavern may be more readily (and quickly) withdrawn, and caverns may be replenished with natural gas more quickly than in either of the other types of storage facilities.
Moreover, salt caverns can readily begin flowing gas on as little as one hour’s notice, which is useful in emergency situations or during unexpected short-term demand surges. Salt caverns may also be replenished more quickly than other types of underground storage facilities.Typically, a salt cavern will provide a high withdrawal rate and a high injection rate relative to the working gas capacity of the cavern. Most salt cavern storage facilities have been developed in salt dome formations located in the Gulf Coast states of the United States.
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Salt caverns have also been formed (by a leaching process) in bedded salt formations in Northeastern, Midwestern, and Southwestern states.Salt formation storage facilities make up about 10% of the natural gas storage facilities. These subsurface salt formations provide very high withdrawal and injection rates.
Subsurface caverns present a drilling risk, presenting a unique problem to seismic imaging. They have several characteristics which handicap imaging: a.They are typically shallow; b.They are three-dimensional in shape, not flat-lying; c.Since they are voids, they have a large acoustic impedance contrast with the enclosing rocks; and d.They are not the primary target of investigation.Since near-surface caverns are not the primary objective, the seismic survey is not designed to image them.
Because they are at shallow depths, the seismic fold (or multiplicity) of the data reflected from them is low and lacks large shot-receiver offsets. Hence, there exist few traces to stack at their depth. Their large impedance contrast generates strong reflections, while their shape scatters the impingent seismic energy. All these contribute to difficulty in focusing their images during seismic migration processing. Worse, they adversely affect the imaging of the underlying reservoir target.
In the Arabian Peninsula, open caverns occur so close to the surface that oftentimes their roofs breach the surface. The entire axial spine of the giant Ghawar Field anticline is dotted with numerous collapsed caverns (karst) and open caverns, that the resulting seismic image of the principal Arab-D carbonate oil reservoir and the deeper Khuff and pre-Khuff clastic gas reservoirs appear incoherent and uncertain. Figure 8.3 shows an example of an open cavern on the Arabian Peninsula and its expression on seismic data indicated with arrows.
Such caverns when they are buried deeper pose drilling hazards in wells. These are predicted from 3D seismic data, ahead of the drill bit. Shallow collapse feature and its effect on seismic reflection data (arrow). Courtesy: Saudi Aramco (Personal communication).When a drilling project critically requires an accurate image of the shallow subsurface, a separate seismic survey, using high-resolution, low-energy, and low-effort seismic techniques, such as those applied for civil engineering and groundwater work, may be conducted. Instead of a heavy vibrator truck as a seismic source, small percussion or explosive sources are used. Shotgun blasts, blasting cap explosions, heavy weights dropped from a small height are some of these sources of seismic energy.
Instead of hundreds or thousands of geophone receivers, a few dozen receivers suffice. The reduced hardware requirements and scope of operations require vastly reduced manpower to conduct the survey. However, the data acquired undergo the same processing as that for the deep seismic survey because the experiment remains the same and the goal is similar, to acquire an image of the subsurface.As in all aspects of reservoir engineering work, data relevant to a specific objective (in this case, drilling hazards) from all sources should be considered before a course of action is taken. The structural images, lithologic predictions, and other inferences from geophysics should complement the thorough analysis of geologic data and previous drilling experience in order to fully illuminate the hazard problem.
As a tool that provides abundant, but indirect, measurements of the regions not actually sampled by existing wellbores, geophysics contributes significantly to the understanding of drilling hazards, but only when properly integrated with all other data. Kamel Bennaceur, in, 2014 26.7.4 Other Storage OptionsOther CO 2 disposal options include other geological media, ocean storage, mineral carbonation, algal bio-sequestration and industrial uses.
26.7.4.1 Other Geological MediaSalt caverns have been used for hydrocarbon products for decades. The low capacity of the caverns, despite high injectivity, their depth and concerns about the containment of CO 2 limit their use for storage. Abandoned mines are also unsuitable, due to the inadequacy of sealed shafts to prevent CO 2 leakage. Basalts have a large worldwide occurrence. Their low permeability (mainly from fissures and fractures) and low porosity do not provide a favourable media for CO 2 injection.
Further research is required, especially in relation to mineral carbonation. 26.7.4.2 Ocean StorageThe principle is to transport the CO 2 to an offshore site, where it is injected into the water column or the sea floor, at water depths generally greater than 1000 m. The 2005 IPCC SRCCS 6 gives a summary of the state of knowledge in ocean CO 2 storage.
Adverse impact on the marine ecosystem (and the whole earth system) through increased ocean acidity is not well understood, and therefore, ocean storage is not considered as an adequate option. 26.7.4.3 Mineral CarbonationThe concept of mineral carbonation is based on the reaction of ground magnesium and calcium silicate with CO 2 to form solid carbonates.
The process requires the milling of a mineral ore and reaction with a concentrated CO 2 stream. However, the process yields are large in terms of volume of materials. A total of (1.6 to 3.7) t of silicate needs to be mined for each tonne of CO 2, and the reaction generates (2.6 to 4.7) t of material. 26.7.4.4 Algal Bio-SequestrationUse of coccolithphorid algae because of their growth rate and CO 2 uptake, as well as their potential to use a feedstock with a lower CO 2 purity, has been proposed for an efficient conversion of CO 2 into carbonates.
Research co-funded by the USDOE is being carried out to determine the most suitable algal species, as well as the potential for biofuel to be generated from the algae. 26.7.4.5 Industrial UsesWithin the fast-growing industrial gas business, CO 2 is third by volume used, after oxygen and nitrogen.
Applications of CO 2 include food and beverage, horticulture, welding and safety devices. The source of the CO 2 is either from high concentration industrial plants (ammonia, hydrogen) or from CO 2 wells. The volume for such applications is, however, small compared to the storage requirements (100–200 Mta −1 of CO 2 vs several gigatonne). Other applications discussed earlier in this chapter are related to cement production. Tunnels and rock caverns are important construction elements in many large-scale hydropower projects: headrace/tailrace tunnels, access tunnels, powerhouse, surge shafts, power cables and ventilation shafts.
In Norway, nearly all large-scale hydropower plants have been built underground since 1960. In 2002 there were 500 underground hydropower plants worldwide, about 40% of these were then found in Norway 10. An example showing an underground powerhouse is shown in Fig.
Typical layout of tunnel system and rock caverns is shown in Fig. Tunneling technology has evolved from traditional drill-and-blast technology to the use of full-face tunnel boring machines (TBM), increasing speed of tunneling and lowering cost.
An underground hydropower plant—Typical layout of tunnel system 10.Today, there is also an interesting technology development for “microtunnels” that can be used to replace pipes and penstocks for small hydropower plants (. Patricia Kambesis, in, 2012Lechuguilla Cave in Carlsbad Caverns National Park, Guadalupe Mountains, New Mexico, has a 2010 surveyed length of 130 km. It is a hypogene cave, formed by uprising H 2S-bearing fluids which oxidize to form sulfuric acid when they reach oxygen-bearing meteoric water. The cave is formed in the Permian Capitan Reef Complex. Argon-argon dating suggests that the cave is on the order of 5 million years old. Lechuguilla Cave exhibits dramatic mineralization, particularly gypsum chandeliers, native sulfur, and many massive calcite speleothems. Of particular interest is the microbiology of the cave where microbes, present and past, formed without surface interactions.Keywordshypogene caves; Guadalupe Mountains; microbiology; chandeliers; sulfur; gypsum speleothems.
Patricia Kambesis, in, 2019 AbstractLechuguilla Cave in Carlbad Caverns National Park, Guadalupe Mountains, New Mexico, has a 2017 surveyed length of 245 km. It is a hypogene cave, formed by up-rising H 2S-bearing fluids which oxidize to form sulfuric acid when they reach oxygen-bearing meteoric water. The cave is formed in the Permian Capitan Reef Complex. Argon-argon dating suggests that the cave is on the order of 5 million years old. Lechuguilla Cave exhibits dramatic mineralization, particularly gypsum chandeliers, native sulfur, and many massive calcite speleothems. Of particular interest is the microbiology of the cave where microbes, present and past, formed without surface interactions.
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