Changes

==Factors influencing rock-water reactions==

==Factors influencing rock-water reactions==

Mineral fines that contribute to permeability reduction can be composed of clay, quartz, feldspar, or carbonate. Nonclay fines have no significant surface charge, and commercial clay stabilizers will not prevent their migration. Detrital clays forming the rock framework normally have little impact on rock-fluid reactions. Authigenic clays, however, line, fill, or bridge pores. They are exposed to extraneous pore fluids with which they may react.<ref name=Eslinger_etal_1988>Eslinger, E., and D. Pevear, 1988, Clay minerals for petroleum geologists and engineers: Society fo Economic Paleontologists and Mineralogists, Short Course Notes No. 22.</ref> Expanding clays (smectites and mixed layer clays containing smectites) can reduce cross-sectional areas of pore throats and thus permeability. More important, as they expand, they often contribute mobile fines. These fines along with illite and kaolinite (which have lesser to no swelling tendency) are the primary maerials that disperse, migrate, bridge, and impair permeability.

Mineral fines that contribute to permeability reduction can be composed of clay, [[quartz]], feldspar, or carbonate. Nonclay fines have no significant surface charge, and commercial clay stabilizers will not prevent their migration. Detrital clays forming the rock framework normally have little impact on rock-fluid reactions. Authigenic clays, however, line, fill, or bridge pores. They are exposed to extraneous pore fluids with which they may react.<ref name=Eslinger_etal_1988>Eslinger, E., and D. Pevear, 1988, Clay minerals for petroleum geologists and engineers: Society fo Economic Paleontologists and Mineralogists, Short Course Notes No. 22.</ref> Expanding clays (smectites and mixed layer clays containing smectites) can reduce cross-sectional areas of pore throats and thus permeability. More important, as they expand, they often contribute mobile fines. These fines along with illite and kaolinite (which have lesser to no swelling tendency) are the primary maerials that disperse, migrate, bridge, and impair permeability.

==Problem prevention and correction==

==Problem prevention and correction==

| Clay swelling (water sensitive) || Smectite lllite-Smectite Chlorite-Smectite lllite Kaolinite || Fluids and System Freshwater-based fluids Any water with inadequate concentration of cations || Oil-based mud Potassium Ammonium chloride Calcium chloride || Preflush with HCl and NH₄ CI HCI/HF acidize Postflush with NH₄ CI and clay stabilizer

| Clay swelling (water sensitive) || Smectite lllite-Smectite Chlorite-Smectite lllite Kaolinite || Fluids and System Freshwater-based fluids Any water with inadequate concentration of cations || Oil-based mud Potassium Ammonium chloride Calcium chloride || Preflush with HCl and NH₄ CI HCI/HF acidize Postflush with NH₄ CI and clay stabilizer

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| Fines movement (rate sensitive) || Kaolinite lllite Chlorite lllite-smectite Chlorite-smectite Clay size particles of quartz or other minerals || High transient pressure High flow rates || Perforate slightly under-balanced (1000 psi) Increase well rate slowly Maximize perforations per ft Select rate less than critical velocity Use clay stabilizer || Preflush if needed with HCl and NH₄ CI Acidize with HCI/HF Postflush with NH₄ CI and clay stabilizer

| Fines movement (rate sensitive) || Kaolinite lllite Chlorite lllite-smectite Chlorite-smectite Clay size particles of [[quartz]] or other minerals || High transient pressure High flow rates || Perforate slightly under-balanced (1000 psi) Increase well rate slowly Maximize perforations per ft Select rate less than critical velocity Use clay stabilizer || Preflush if needed with HCl and NH₄ CI Acidize with HCI/HF Postflush with NH₄ CI and clay stabilizer

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===Water pH===

===Water pH===

Negative charges exist on clay surfaces, and kaolinite is weakly cemented. Consequently, a repulsive force between quartz and clay promotes clay dispersion and reduced permeability at normal to high pH values. Effects of pH are intensified in low salinity solutions and are less important in high ionic strength solutions. Values of pH greater than 9.0 also result in silica dissolution, with resultant fines release. High pH also promotes formation of oil-water emulsions that reduce flow rate. Thus, it is best to avoid high pH systems.

Negative charges exist on clay surfaces, and kaolinite is weakly cemented. Consequently, a repulsive force between [[quartz]] and clay promotes clay dispersion and reduced permeability at normal to high pH values. Effects of pH are intensified in low salinity solutions and are less important in high ionic strength solutions. Values of pH greater than 9.0 also result in silica dissolution, with resultant fines release. High pH also promotes formation of oil-water emulsions that reduce flow rate. Thus, it is best to avoid high pH systems.

===Temperature effects===

===Temperature effects===

The rate of permeability impairment has been summarized and shown to decrease with increasing temperatures up to [[temperature::200&deg;F]] when brine flows in the presence of oil. It has also been shown that higher temperatures require higher salt content to stabilize clays when only brine flows. Solubility of quartz increases with temperature, and additional fines can be released and mobilized. It is prudent to make evaluation measurements at temperatures expected to exist at operating conditions.

The rate of permeability impairment has been summarized and shown to decrease with increasing temperatures up to [[temperature::200&deg;F]] when brine flows in the presence of oil. It has also been shown that higher temperatures require higher salt content to stabilize clays when only brine flows. Solubility of [[quartz]] increases with temperature, and additional fines can be released and mobilized. It is prudent to make evaluation measurements at temperatures expected to exist at operating conditions.

==See also==

==See also==

[[Category:Laboratory methods]] [[Category:Test content]][[Category:Pages with unformatted tables]]

[[Category:Laboratory methods]] [[Category:Test content]][[Category:Pages with unformatted tables]]