Clay, swelling

Some clay minerals may absorb some of the water contained in the drilling mud. This will cause the clays to swe//and eventually reduce the borehole size to the point where the drill pipe becomes stuck. Prevention mud additives which prevent clay swelling e.g. potassium salt. 

Two types of swelling may occur. Surface hydration is one type of swelling in which water molecules are adsorbed on crystal surfaces. Hydrogen bonding holds a layer of water molecules to the oxygen atoms exposed on the crystal surfaces. Subsequent layers of water molecules align to form a quasi-crystalline structure between unit layers which results in an increased c-spacing. All types of clays swell in this manner. 

T. R. Thomas and K. W. Smith. Method of maintaining subterranean formation permeability and inhibiting clay swelling. Patent US 5211239,1993. 

The effect of pH on both clay swelling and fines production has been widely discussed(89-95). Little consensus is found in this literature. Suggested treatments range from application of fluoboric acid(96) to 15% KOH(92) solutions — both treatments are believed to create a protective silicate film that inhibits release of fines. Polyacrylate polymers can provide protection against swelling of smectite clays and shales(97-100). 

When a soil containing 2 1 clays becomes wet, the clays swell shut and water movement through it is extremely slow. In a soil profile, wetting and swelling of this type of clay will prevent downward movement of water and associated contaminants. For this reason, swelling clays are used to seal both landfills and ponds to prevent leaching or leaking. 

Fahing et al. [24] studied the modifier effects in the supercritical fluid extraction of organics from soils and clays. Swelling experiments showed that unmodified carbon dioxide did not cause swelling of the soil whereas carbon dioxide modified with water did cause rapid swelling of soil, thereby facilitating extraction of the organics. 

Hot rolling particles from the recovery test on the cuttings were used. Samples were extruded in a CT 15 compressometer device at a rate of 40 mm /min where the pressure necessary to extrude the particles was recorded. The harder the particles, the higher the pressure, the better the protection with regard to penetration of water, and the better the inhibiting effect on clay swelling. Testing results are provided in Table 2. 

For many systems this is indeed observed. There are, however, important exceptions. One such exception is the swelling of clay [159-161], In the presence of water or even water vapor, clay swells even at high salt concentrations. This cannot be understood based on DLVO theory. To understand phenomena liken the swelling of clay we have to consider the molecular nature of the solvent molecules involved. 

The more concentrated is the system, the better statistics must be involved. Here (for higher electrolyte concentrations) a family of HNC approximation approximations may be mentioned, which demonstrated very good agreement with the Monte Carlo results. They have also been checked with experiments on the interaction between two mica sheets in electrolytes (for CaCb electrolyte see [37]), and found a variety of applications. For example, a proper account of the ion distributions allows to explain such phenomenon as a clay swelling in the presence of an electrolyte, while the standard DLYO description fails [36]. Also these ideas have been utilized when studying different biological systems [38-40]. 

For soil systems contaminated with Na+, kinematic viscosity is not significantly affected, thus the components controlling water flow velocity are the hydraulic gradient (A< >/AX) and soil permeability (k). The latter component (k) is influenced by clay dispersion, migration, and clay swelling. These processes may cause considerable alteration to such soil matrix characteristics as porosity, pore-size distribution, tortuosity, and void shape. 

The increase in soil pH could be implicated in increasing soil dispersion as well as in increasing clay-swelling potential. This is likely because of the removal of Al-OH polymers from the interlayer. The presence of Al-OH polymers at the lower pH values may limit interlayer swelling. Clays that have the basic 2 1 mineral structure may exhibit limited expansion because of the presence of Al-hydroxy islands which block their interlayer spaces. It is well known that these Al-hydroxy components are removed at low or high pH through dissolution mechanisms. This interlayer removal... 

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