Bridging agents

These compounds should be dissolvable in a clean-up solution containing a quaternary organic ammonium salt, or simply ammonium chloride [1749]. The solubilities of some selected particulate bridging agents are shown in Table 9-1. A chelating agent such as citric acid or its salts is also included in the clean-up solution. 

However, production engineers have been reluctant to use particle bridging because of the possibility of particle transport into the formation, resulting in formation damage and/or costly and often ineffective stimulation treatments. A particle bridging fluid has been developed that quickly and effectively controls fluid loss in a wide range of permeabilities and pore diameters [916]. 

Water-soluble organic polymers, sueh as hydroxethylcellulose, have been used to slow the leak-off rate of clear brines into permeable formations. Fluid loss or leak-off, however, can be effectively controlled only by bridging the pore openings with rigid or semirigid particles of sufficient size and number. 

Particulate bridging agent Aqueous ammonium salt clean-up solution Solubility [g/lOOml] 

Magnesium oxide 1.3 M ammonium chloride plus 1 M sodium citrate 2.8 

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Molecular weights of polymers that function as bridging agents between particles are ca 10 —10. Ionic copolymers of acrylamide are the most significant commercially (see Acrylamide POLYMERS). Cationic comonomers include (2-methacryloyloxyethyl)trimethylammonium salts, diethyl aminoethyl methacrylate [105-16-8], and dimethyldiallylammonium chloride [7398-69-8], anionic comonomers include acryUc acid [79-10-7] and its salts. Both types of polyacrylamides, but especially the anionic, can be more effective in the presence of alum (10,11). Polyetbylenimine and vinylpyridine polymers, eg, po1y(1,2-dimethy1-5-viny1pyridiniiim methyl sulfa te) [27056-62-8] are effective but are used less frequentiy. 

Figure 7.10. (a) Bridging agents, (b) Cross-linking initiators, (c) Catalytic cross-linking agents, (d)... 

The filter-cake formed in this process, however, is highly dispersible to the produced fluid and thus is effectively removed by placing the well on production. No acid treatment or other removal techniques are required. The primary bridging agent in this fluid is a sized calcium carbonate with particle sizes capable of initiating bridging in pore diameters in excess of 100 p. 

A similar experiment using a diamine (ethylenediamine) as the bridging agent instead of a diacid, in combination with isobutyraldehyde and acetic acid, led to the isolation of macrocycle 114 (Scheme 20). 

By linking edge-sharing octahedra to form a layer as in Fig. 16.8, all X atoms act as bridging agents, and every one of them simultaneously belongs to two octahedra. This kind of layer encloses voids that have an octahedral shape (see also the figure on the cover). The composition of the layer is MX3 Numerous trichlorides, tribromides... 

The above is not to underestimate the role of clay in the hot water process. Tar sands of high clay content generally are difficult to process, owing partly to the tendency of clay to stabilize oil and water emulsions. In addition, polyvalent metal ions act as bridging agents between the oil and clay, particularly at low pH. The association of clay with the oil retards the attachment of air as well as increasing the density of the oil particles. This mechanism is discussed in detail in Ref. 2. 

The approach to obtaining adhesion is to use an intermediate chemical compound between the glass and the matrix. The bridging agents used are organofunctional silanes. These materials bond to the glass surface as well as to the matrix. 

Removal of particles from liquids, as in the formation of pellet-like floes from clay in water by the use of polymeric bridging agents. 

Fig. 8.1. Agglomeration phase diagram [6]. Phenomena which occur as increasing amounts of an immiscible wetting liquid are added to a solids suspension. A typical example is fine coal in water to which an organic liquid is added as bridging agent.

Fractionation of particle of clays in water using polymeric bridging agents selective oil agglomeration... 

A typical application for these filter aids is the filtration of solids from antibiotic fermentation broths, where the average particle size is 1-2 microns and solids concentration are 5-10%. Being hard to filter and often slimy, fermentation broths can also be charged with polymeric bridging agents to agglomerate the solids, thereby reducing the quantities of filter aid required. 

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