Fines hydrodynamic forces

Part of the complication with gas-solid systems arises from the fact that the purely hydrodynamic forces acting on the particles are relatively small compared with frictional forces between particles, electrostatic forces and surface forces which play a much more dominant role when the particles are very fine. As the gas velocity in a fluidised bed is... 

Chemical barriers use chemicals that solidify the oil and prevent its spread. Large amounts of chemicals are required, however, and the potential for containment is low. Net booms made from fine nets are used to collect viscous oils, tar balls, and oiled debris without having the large hydrodynamic forces of a solid boom. Oil trawls are similar to net booms, but are made in the shape of a U so that oil is contained in the net pocket. 

Mechanical Fines Migration. A fine particle attached to the surface of the sand particle is subjected to several hydrodynamic forces (51, 65). The two major hydrodynamic forces that act on a fine particle are the lift force and the viscous-drag force (Figure 2). The lift force, Fl, acts in a direction normal to the flow direction ([/-direction) and its magnitude is (66)... 

The nature and properties of common clay minerals found in petroleum reservoirs are briefly discussed to set the stage for a review of the colloidal and hydrodynamic forces acting on the fine particles. This is followed by a review of reported experimental studies of permeability damage by fines movement under purely hydrodynamic forces. 

To determine the conditions for fine particle detachment the magnitude of the hydrodynamic forces near a rock grain surface have been estimated by Cerda (27) assuming spherical particles and rock porosities in the range 0.2 to 0.4 as... 

As discussed in the preceding section, the hydrodynamic force exerted by a fluid flowing through a pore on a fine particle attached to the wall of the pore is directly proportional to the velocity of the fluid and its... 

In agreement with the statements made regarding the influence of hydrodynamic forces in the previous section, Khilar et al. (18, 36) have found at best a weak dependence of CSC on the superficial velocity (for 3 to 568 cm/h). Because in practise one deals with solutions of mixed salts, Khilar et al. (18) have introduced the critical total ionic strength (CTIS) to improve the predictions for solutions containing multivalent ions such as calcium. A number of studies have shown that where freshwater flooding of sandstones may drastically decrease permeability due to fines migration, suitable adjustment of the flooding solution composition to above the CSC or CTIS can decrease or eliminate the permeability reduction (12, 18, 36). In these cases the solution compositions are adjusted so as to reduce the Zeta potential at the particle surfaces, which reduces the repulsive colloidal forces. Thus the same factors that... 

Two types of flow are recognized thixotropy, defined as a decrease of apparent viscosity under shear stress, followed by a gradual recovery when the stress is removed, and its opposite, anti-thixotropy, or rheopexy. Both are related to molecular or macroscopic changes in interactions. In thixotropic liquids, the aggregate bonding must be weak enough to be broken by flow-induced hydrodynamic forces. If dispersion is fine, even slight interactions may produce thixotropic effects. When... 

The release or detachment of the fine particles from the collector surface is assumed to be induced by the hydrodynamic forces in the case of non-Brownian particles or by the colloidal forces in the case of Brownian particles [131]. For non-Brownian fine particles, the rate of hydrodynamic particle entrainment is considered to be proportional to the difference between the wall shear stress and the critical shear stress [123] ... 

Optimum particle size and density Mixture of two groups of particles (e.g., add fine particles to a coarse particle bed and vice versa) Modification of particle size distributions Use of fine particles (with interparticle forces to be smaller than the hydrodynamic forces)... 

Regardless of the nature of the adhesive force (Krupp, 1967 Ranada, 1986) holding the lines onto the surface of the coarse particle, an analysis of force balance on the fine particle between adhesion, hydrodynamic drag, and gravity (Kwauk, 1984,1986 Xia and Kwauk, 1985) lent support to the phenomena enumerated above on the varying degree of surface coverage of the coarse particle by the fine particles. 

The behavior of particles under the simultaneous effect of field forces and lift forces can vary with the nature of different applied primary field forces [298]. The force acting on the particles is proportional to the third power of the particle diameter in S-FFF, but only to the first power of the particle diameter in Fl-FFF thus indicating that S-FFF is probably best suited for a fine balance between the external field and hydrodynamic lift forces. 

The system of hydrodynamic secondary hydrocarbon migration, whether the hydrocarbons move in separate phase, in very fine suspension or in aqueous solution, is influenced by the porosity and permeability distribution in a sedimentary basin, and the magnitude and direction of the net driving force for groundwater flow. As a consequence, the different processes and associated forces that are responsible for the hydrodynamic conditions in a sedimentary basin also determine to a greater or less extent the characteristics of the hydrocarbon migration system in a hydrodynamic basin (Sections 4.3.4.1, 4.S.4.2 and4.3.4.3). 

---