Hydrate Inhibition Using Salts

The action of salts as inhibitors is somewhat different than that of alcohols or glycols. The salt ionizes in solution and interacts with the dipoles of the water molecules with a much stronger Coulombic bond than either the hydrogen bond or the van der Waals forces that cause clustering around the apolar solute molecule. The stronger bonds of water with salt ions inhibit hydrate formation water is attracted to ions more than water is attracted to the hydrate structure. 

As a secondary effect, this clustering also causes a decrease in the solubility of potential hydrate guest molecules in water, a phenomenon known as salting-out. Both ion clustering and salting out combine to require substantially more subcooling to overcome the stmctural changes and cause hydrates to form. 

For an accurate estimate of salt effects, the computer program (enclosed with this monograph) should be used, incorporating the methods in Chapter 5, and in the User s Manual in the book s CD. However, a rapid estimate for the depression of salt on hydrate equilibrium may be obtained by knowledge of the depression of salt on ice equilibrium, using the method in this section. 

Pieroen (1955) provided a theoretical foundation for the Hammerschmidt equation, showing that when the solubility of one phase in the other is neglected, a nonvaporizing inhibitor such as salt can be approximated as 

Example 4.5 Short Cut Calculation of Hydrate Formation Conditions with Salt 

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Several means of hydrate prevention and dissociation are discussed in detail in Chapter 8. In the present section we consider the lowering of the three-phase (Lw-H-V) temperature or the increase of the Lw-H-V pressure via an inhibitor. In this section we consider only thermodynamic inhibitors such as alcohols, glycols, or salts. For kinetic inhibition using LDHIs, such as KIs or A As, the reader is referred to Chapter 8. 

Seawater muds are commonly used on offshore locations, which eliminate the necessity of transporting large quantities of freshwater to the drilling location. The other advantage of seawater muds is their inhibition to the hydration and dispersion of clays, because of the salt concentration in seawater. The typical composition of seawater is presented in Table 4-48 most of the hardness of seawater is due to magnesium. 

Solutions of TKPP have been shown to have unique and advantageous properties for use in formulating a wide variety of well fluids. Its reasonable cost, worldwide availability, and nontoxic properties make it a preferred additive for use in many petroleum applications. It has been shown to be a most effective salt with respect to inhibiting hydration and swelling of clay minerals commonly encountered in drilling operations and/or reservoirs. Avoiding clay problems is the major impetus for the incorporation of potassium ions in well fluids, and the use of TKPP provides advantages over and above those available from other potassium salts. 

The thesis of Ballard (2002) details this calculation method, which includes multiphase systems, solid phases including ice and salts, and thermodynamic inhibition. The CSMGem (the last three initials are the first letters of Gibbs energy minimization ) User s Manual, included in the CD in the endpapers, and the examples of hydrate calculation shown in the Appendix A, enable the reader to use the CD programs. 

Experimental (P-T) data do not adequately characterize hydrates, particularly in fine-grained sediments. Clennell et al. (1999) used surface effects to explain this discrepancy. Inhibition by localized salt could also explain this discrepancy. 

The tetrasodium salt of carbonylbisphosphonate was originally synthesized by Quimby et al. [76], using hydrolysis of a tetraalkyl dichloromethylenebisphos-phonate in aqueous NaOH. In aqueous solution, the yellow ketone form reversibly converts to its colorless hydrate at acidic pH [76], a process which can be assessed by a combination of 31P-NMR and uv-visible spectroscopy at pH 7, the ketone predominates [93]. The salt moderately inhibits HIV reverse transcriptase in a p24 assay, whereas the parent methylene compound is inactive [64], displays some activity vs the pyrophosphate-dependent phosphofructose kinase of the parasite T. gondii [94] and has found use as a selective inhibitor of PCNA-independent DNA polymerase 6, allowing its enzyme activity to be distinguished from that of DNA polymerase a [95]. 

In addition to salts, alcohols, and polymers, the presence of a porous medium will also have an inhibiting effect on the formation of gas hydrates. Clarke, Pooladi-Darvish, Bishnoi derived the following expression for the activity of water in a pore of radius r, and used it along with the model of van der Waals and Platteeuw to model the incipient conditions for... 

In summary, it is clear that massive amounts of traditional NSAIDs and COX-2 specific inhibitors will continue to be consumed worldwide. Because these agents inhibit renal prostaglandin synthesis, they affect salt and water homeostasis and renal hemodynamics. This inhibition will have little clinical effect in the majority of patients who are well-hydrated, have good renal function, and no concomitant disease states. However, both traditional NSAIDs and COX-2 specific inhibitors must be used judiciously in patients with compromised renal blood flow. In general, the COX-2 specific inhibitors are well tolerated by the kidney and it is only in the clinical setting of significant pre-existing renal im-... 

For MeOH-salt systems, two other produeed water samples were used. The produced water samples were taken from the downstream of a pipeline that was inhibited with MeOH, and eontained multiple salts and an unknown amount of a CL The C-V device measured the first one (PWS-1) with 2.9 mass% of salts and 22.2 mass% of MeOH, and the second one (PWS-2) with 3.0 mass% of salts and 23.0 mass% of MeOH. For PWS-1, two hydrate phase boundaries were determined by the C-V deviee and the freezing point depression (FPD) method [14], for a typical natural gas that was composed of methane (88.3 mol%), ethane (5.4 mol%), propane (1.5 mol%), isobutene (0.2 mol%), normal butane (0.3 mol%), isopentane (0.1 mol%), normal pentane (0.09 mol%), nitrogen (2.39 mol%), carbon dioxide (1.72 mol%). For PWS-2 with the same natural gas, the C-V device determined the hydrate phase boimdary, and one hydrate... 

Zinc yellow is a hydrated double salt of zinc and potassium chromate used principally in corrosion-inhibiting metal primers. It is becoming one ofthe few pigments permitted for use on steel connected in houses or apartments. The pigment is greenish yellow and offers poor opacity. 

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