Alkali rock interactions

Surfactant Mixing Rules. The petroleum soaps produced in alkaline flooding have an extremely low optimal salinity. For instance, most acidic crude oils will have optimal phase behavior at a sodium hydroxide concentration of approximately 0.05 wt% in distilled water. At that concentration (about pH 12) essentially all of the acidic components in the oil have reacted, and type HI phase behavior occurs. An increase in sodium hydroxide concentration increases the ionic strength and is equivalent to an increase in salinity because more petroleum soap is not produced. As salinity increases, the petroleum soaps become much less soluble in the aqueous phase than in the oil phase, and a shift to over-optimum or type H(+) behavior occurs. The water in most oil reservoirs contains significant quantities of dissolved solids, resulting in increased IFT. Interfacial tension is also increased because high concentrations of alkali are required to counter the effect of losses due to alkali-rock interactions. 

Chemical compositions of major elements (alkali, alkali earth elements. Si) in back-arc and midoceanic ridge hydrothermal solutions are not so different (Table 2.15). This is thought to be due to the effect of water-rock interaction. For example, Berndt et al. (1989) have shown that mQ i+ of midoceanic ridge hydrothermal fluids is controlled by anorthite-epidote equilibrium (Fig. 2.37). Figure 2.37 shows that /Mca2+/m + of back-arc hydrothermal fluids is also controlled by this equilibrium. 

Schweda P. (1989) Kinetics of alkali feldspar dissolution at low temperature. In Proc. 6th Int. Symp. Water/Rock Interact. (ed. D. L. Miles). A. A. Balkema, Rotterdam, Brookfield, Vt, pp. 609 -612. 

Dissolution rate constants for major elements are summarized as a function of temperature in Fig. 2. Apparent activation energies have the same relationship as dissolution rate. Alkali metal and alkali earth metal ion have -20 to 40 kJ/mol apparent activation energy, due to a diffusion effect from the mineral surface. The existing reaction condition does not correspond to the critical reaction rate, but this condition is more applicable for natural water-rock interactions, because the nature of incongruent dissolution on the mineral surface controls fluid chemistry and metastable reaction processes. 

Published experimental studies of mineral/cal-cium hydroxide reactions show that at low temperatures (below 110°C), the chief reaction products are calcium silicate hydrate (CSH) gels, while zeolites and feldspars are formed at higher temperatures and in the presence of alkalis NaOH and KOH. The phase identifications have however often been made by low resolution or bulk methods, neither of which are ideal for such material. Published results of numerical simulations are in broad agreement with those of experimental studies of cement/ rock interaction. These models predict that CSH gels will be replaced by zeolites and maybe feldspars as plume chemistry evolves. 

The problem of crustal contamination is particularly acute for low mg continental flood basalts and smaller volume continental tholeiitic basalts, both of which have low trace-element concentrations (see Sections 3.03.3.2.3 and 3.03.3.3). The issue is less critical for many smaller volume continental rocks, such as kimberlites and alkali basalts, which have much higher abundances of many trace elements. As a result of their high strontium and neodymium content, for example, the isotopic compositions of these elements in kimberlites and alkali basalts are relatively insensitive to modification during crustal contamination. Conversely, the osmium and lead concentration of basaltic magmas are so low that these isotope systems are particularly vulnerable to modification by interaction with cmstal rocks (McBride et al, 2001 Chesley et al, 2002) hence these systems provide relatively sensitive indicators of crustal assimilation. 

Other products of interaction of various rocks with bat excreta are taranakite (Sakae and Sudo, 1975), dittmarite (Mrose, 1971), mirabilite (Hutchinson, 1950), biphosphammite (Hutchinson, 1950 Pryce, 1972), phosphammite, struvite, newberyite, bobierrite, schertelite, hannayite, stercorite, monetite, whitlockite and brushite. It is noticeable (Table 3.1.1) that most of these mineral include the ammonium ion, which results from decomposition of urea and/or uric acid, and later the more stable minerals (Bobierrite, for example) persist after leaching of alkali ions (including NHJ) has been accomplished. 

One rock-alkali interaction is described by the sodium/hydrogen-base exchange (hydroxide-exchange),... 

Interaction of alkali with rock minerals in reservoir sand is complicated. Somerton and Radke (11) classified these interactions into surface exchange and hydrolysis, congruent and in congruent dissolution reactiaiSr and insoluble salt formation by reaction with hardness ions in the pore fluids and exchanged from sand surfaces. These interactions may also be classified into reversible adsorption or non-reversible chemical consurrp-tion, and kinetic controlled or instantaneous reactions. 

Color centers in alkali halide crystals are based on a halide ion vacancy in the crystal lattice of rock-salt structure (Fig. 5.76). If a single electron is trapped at such a vacancy, its energy levels result in new absorption lines in the visible spectrum, broadened to bands by the interaction with phonons. Since these visible absorption bands, which are caused by the trapped electrons and which are absent in the spectrum of the ideal crystal lattice, make the crystal appear colored, these imperfections in the lattice are called F-centers (from the German word Farbe for color) [5.138]. These F-centers have very small oscillator strengths for electronic transitions, therefore they are not suited as active laser materials. 

This article reviews the relevant literature on cement/rock and mineral/alkali interaction, and presents the results of experimental and archaeological analogue studies in which Analytical Transmission Electron Microscopy (ATEM) has been used to characterize C-A-S-H phases. 

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