Permeability bentonites

This example is to test the swelling effects under capillary pressures up to 10 Pa occurring in extremely low-permeable bentonite materials. For this purpose, a simple 1-D case is set up. A one meter long bentonite column is heated on the left hand side. Element discretization length is 0.01m. The initial conditions of the system are atmospheric gas pressure, full liquid saturation and a temperature of 12°C. The heater has a constant temperature of 1(X) C. Flow boundary conditions on the left side are gas pressure of 10 Pa and 15% liquid saturation. On the right side we have atmospheric pressure, full liquid saturation and no diffusive heat flux. As a consequence, a typical desaturation process of bentonite is triggered. The complete set of initial and boundary conditions and the material properties for this example was described in detail by Kolditz De Jonge (2003). 

The use of polyisoprene or butadiene-styrene latex with bentonite or chalk filler and polyoxypropylene as an additive has been used in a plugging solution for oil and gas wells [1042]. The solution can be pumped but coagulates within the formation at temperatures of 100° C within 2 hours. This causes a reduction in permeability. The formulation is particularly useful in deep oil deposits. 

Bentonite is dry blended to the cement. The addition of bentonite requires more water. Bentonite has been used up to 25% by weight. The additive also increases the viscosity of the slurry. High amounts of bentonite increase the permeability and reduce the final strength, however. Therefore high concentrations of bentonite are not recommended. 

Bentonite is the name for a hydrous aluminum silicate comprised principally of the clay mineral montmorillonite, notable for its ability to swell in water and to form a very low-permeability seal." It is available as powder, granule (chip), or pellets. Powder and granule sizes are produced by processing after mining. Bentonite powder... 

Already during drilling and well construction there are certain risks for clogging of the aquifer porosity. As illustrated in Figure 41, fines may invade into permeable beds decrease the yield capacity. A well known such clogging additive to the drilling mud is bentonite, which ones invaded is very difficult to clean out. For this reason it is much better to use polymers in the mud. 

Subsurface barriers, low-permeability cutoff walls or diversions below ground are used to contain, capture, or redirect groundwater flow. The most common method uses bentonite slurry... 

Grouted barriers use a variety of fluids injected into a rock or soil mass, which is set in place to reduce water flow and strengthen the formation. Grouted barriers are seldom used for containing groundwater flow in unconsolidated materials around hazardous waste sites because they cost more and have lower permeability than bentonite slurry walls. Nevertheless, they are suited to sealing voids in rock for waste sites remediation. 

For compacted, low-permeability soil liners, the U.S. EPA draft guidance recommends natural soil materials, such as clays and silts. However, soils amended or blended with different additives (e.g., lime, cement, bentonite clays, and borrow clays) may also meet the current selection criteria of low hydraulic conductivity, or permeability, and sufficient thickness to prevent hazardous constituent migration out of the landfill unit. Therefore, U.S. EPA does not exclude compacted soil liners that contain these amendments. Additional factors affecting the design and construction of CCLs include plasticity index (PI), Atterburg limits, grain sizes, clay mineralogy, and attenuation properties. 

Calcium bentonite, as though more permeable than sodium bentonite, has also been used for soil blends. Approximately twice as much calcium bentonite typically is needed however, to achieve a hydraulic conductivity comparable with that of sodium bentonite. One problem with using sodium bentonite, however, is its vulnerability to attack by chemicals and waste leachates, a problem that will be discussed later. 

Since calcium bentonite, typically, is 100-1000 times more permeable than sodium bentonite, the introduction of this permeating liquid could change hydraulic conductivity substantially. 

Foamed cement slurries have been used to provide a low density cement slurry to reduce permeability damage to highly sensitive formations through reduced fluid loss (29). Glass microspheres have also been used to substantially reduce cement slurry density (30, 31). Other additives which reduce cement slurry density to a lesser extent include bentonite, fly ash, silicates, perlite, gilsonite, diatomaceous earth, and oil emulsions (see citations in reference 29). 

A Waterloo Barrier was installed to a depth of 32 ft at Canadian Forces Base Borden in Ontario, Canada. The sheet piles interlocked to form a cell that was 18 ft long and 5 ft wide. The joints were sealed with a bentonite-base sealant. The barrier was used to control groundwater flow to allow for the installation of a permeable reactive barrier (PRB). After the PRB was installed, the Waterloo Barrier was removed and treatment began. The installation costs for the PRB were 30,000. This total included the installation and removal costs for the Waterloo Barrier but excluded the costs for labor and the reactive material used in the PRB (D21297F, p. 33). 

Bentonite rocks have many uses in the chemical and oil industries and also in agriculture and environmental protection. The usefulness of bentonite for each of these applications is based on its interfacial properties. These properties are determined by geological origin, chemical and mineral composition (especially montmorillonite content), and particle size distribution, and they include the specific surface area (internal and external), cation-exchange capacity (CEC), acid-base properties of the edge sites, viscosity, swelling, water permeability, adsorption of different substances, and migration rate of soluble substances in bentonite clay. 

Bentonite and attapulgite clays are used to modify viscosity of coatings. Mica clay has a platelet structure and can be useful in reducing permeability of paint films. 

DRILL MUD A dense fluid or slurry used in rotary drilling to prevent caving of the bore hole walls, as a circulation medium to carry cuttings away from the bit and out of the hole, and to seal fractures or permeable formations, or both, preventing loss of circulation fluid. The most common drill mud is a water-bentonite mixture, however, many other materials may be added or substituted to increase density or decrease viscosity. 

The permeability of grout seals is further discussed by Kurt and Johnson (1982) (22). It is recommended that cement seals be used, and bentonite seals be avoided. 

Figure 53. Time dependence of normalized permeability of water-saturated sandstone samples during dynamic filtration of various water-based drilling fluids and injection of filtrate. (A) 20 gjL bentonite suspension (B) 40 gjL bentonite suspension (C) injection of fresh-water filtrate (D) 40 g/L bentonite in 0.51 M NaCl. (Reproduced with permission from reference 150. Copyright 1992 Society of Petroleum Engineers.)...

It has been shown that the hydration of the bentonite buffer was essentially independent of the heterogeneous nature of the rock hydraulic conductivity features. This is explained by the fact that the rock matrix permeability is higher than the saturated bentonite permeability. Some 3D analyses performed, where the heterogeneous permeability features of the rock have been included, tend to support also this conclusion. 

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