Claying or caking

Several methods may be applied to prevent sedimentation and the formation of clays or cakes in a suspension [42, 43] ... 

With state (b), the particles are uniform and they will settle under gravity, forming a hard sediment (technically referred to as clay or cake ). The repulsive forces between the particles allow them to move past each other until they reach small distances of separation (that are determined by the location of the repulsive barrier). Owing to the small distances between the particles in the sediment it is very difficult to redisperse the suspension by simple shaking. 

Factors that govern the stability of suspension concentrates have been the subject of considerable research [68-70]. Theories of colloid stability could be applied to predict the physical states of these systems on storage. In addition, the problem of sedimentation of SCs has been analyzed at a fundamental level [71]. Since the density of the particles is usually larger than that of the medium (water) SCs tend to separate as a result of sedimentation. The sedimented particles tend to form a compact layer at the bottom of the container (sometimes referred to as clay or cake), which is very difficult to redisperse. It is, therefore, essential to reduce sedimentation and formation of days by incorporation of an antisettling agent. 

Once a dispersion that is stable in the colloid sense has been prepared, the next task is to eliminate claying or caking. This is the consequence of settling of the... 

Fine inorganic materials such as swellable clays and finely divided oxides (silica or alumina), when added to the dispersion medium of coarser suspensions, can eliminate claying or caking. These fine inorganic materials form a three-... 

The invasion of particles can be eliminated either by using solids-free systems or by formation of a competent filter cake on the rock surface. If the components forming the filter cake are correctly chosen and blended, they will form a very effective downhole filter element. This ensures that colloidal sized clays or polymeric materials are retained within the filter cake and do not enter the formation. Further protection is provided by ensuring that a thin filter cake is formed due to low dynamic and static filtrate losses. Thus, the cake may be easily removed when the well is brought into production. Additionally, the filter cake can be soluble in acid or oil. 

Clays or shales have the ability to absorb water, thus causing the instability of wells either because of the swelling of some mineral species or because the supporting pressure is suppressed by modification of the pore pressure. The response of a shale to a water-based fluid depends on its initial water activity and on the composition of the fluid. The behavior of shales can be classified into either deformation mechanisms or transport mechanisms [1765]. Optimization of mud salinity, density, and filter-cake properties is important in achieving optimal shale stability and drilling efficiency with water-based mud. 

The unique design of the tube press allows for this cycle to be amended, however, to include air pressing and/or cake washing. With air pressing, once the initial filtration is complete, air is introduced between the membrane and the cake. The pressure cycle is then repeated. Typically an air press will further reduce the moisture content of china clay by 2.5-8 per cent. The final moisture contents with other materials are shown in Figure 7.25. Water washing, which is used for the removal of soluble salts, is similar to air pressing, except that it is water that is introduced between membrane and cake. 

Soils with a high proportion of fines (clays) can cake and can generate high levels of particulates in off-gases. Some vendors suggest a limit of 30% fines. Above that level, soil must be fed more slowly or should be mixed with coarser soils to decrease the level of fines. 

Low-level oil contamination (5 mg/1) can be removed bypassing the condensate through clay, or diatomaceous earth, either as a bed supported by anthracite, or diatomaceous earth precoat filters supported by filter paper, porous stone, or wire cloth etc. In addition, a small amount of earth is fed continuously with incoming condensate at the filter inlet. The filter cake is later removed by back washing and rinsing. 

A drilling fluid is composed of a carrier fluid and solids (clay or polymer). The carrier fluid carries the solids down the borehole where they block off the pore spaces on the borehole wall. The blockage is referred to as a filter or mud cake. The ideal mud cake will form quickly during construction of the wellbore and prevent intrusion of drilling fluid into the formation. At times additives such as detergents are added to the drilling fluids to counteract some of the formation characteristics such as swelling and stickiness. 

A laboratory oven (Note 1) is equipped with as many clay plates or enameled pie plates or trays as it will accommodate and is adjusted to operate at 98-99° (Notes 2 and 3). When the temperature has become constant the plates are removed, rapidly covered with a layer (not over 3-4 mm. deep) of pulverized (Notfe 4) hydrated oxalic acid, and then quickly replaced in the oven. The temperature will drop slightly for a few minutes (Note 5). After the oven has regained the temperature for which it was adjusted, it is heated for two hours longer at this temperature. The product is then removed, crushed if slightly caked, and quickly bottled. The yield from 100 g. of hydrated oxalic acid is 69-70 g. (96-98 per cent of the theoretical amount) (Note 6). The product is 99.5-100 per cent pure, as indicated by titration with standard alkali. 

Kittitas. Conditioning agents commonly used for reducing the tendency of / N to cake are Kaolin or other forms of clay, and various types of Kieselguhr (qv), such as Kittitas,... 

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