Pore fluid chemistry

The main objective of this research effort was to characterize diagenetic transformations among the various sulfide phases and analyze pore fluid chemistry with respect to depth. In addition, it also examined if the overlying organic-rich Spartina marsh sediments affected the formation of iron sulfides in the underlying sediments. 

Pore fluid chemistries of the various samples are summarized in Figure 4. The distribution of salinities (Figure 4A) within each core is fairly regular but distinct from each of the other cores. 

Franks S.G. and Forester R.W. (1984) Relationships among secondary porosity, pore-fluid chemistry and carbon dioxide, Texas Gulf Coast. In Clastic Diagenesis (eds. D.A. McDonald and R.C. Surdam), pp. 63-79. AAPG, Tulsa, OK. 

Initial conditions were specified to reflect site conditions in 1994 when a major field sampling program took place (Zhu et al., 2002). The domain was divided into four zones (Figure 10.4), reflecting groundwater geochemical zonations observed in the field (Zhu et al., 2002). The pore fluid chemistry and aquifer mineral compositions for each zone are shown in the phreeqc input file (Table 10.3). 

Pore fluid chemistry changes alter chemically sensitive rocks, particularly shales, so that their properties change substantially. 

The need to account for shale properties as well as pore fluid chemistry has led to the suggestion of a descriptive dimensionless parameter, the Reactivity Coefficient (Fam et al. 2003), for shales. 

Thermodynamic calculations can be carried out to determine which solid phases should be dissolving, precipitating, or in equilibrium with the pore fluid chemistry. While these calculations do not guarantee the presence of minerals that are at or above saturation, or the absence of minerals that are undersaturated, they are a very useful indicator of whether it may be worthwhile to search for minerals that could be present in only trace abundance. 

The particular geochemical process of change of zeta potential of soil particle surfaces as a function of soil pH and pore fluid chemistry poses significant complexity to... 

EM rates in the subsurface depend on electric current, soil pore fluid, grain size, ionic mobility, and contamination level. The direction and quantity of contaminant movement are influenced by soil type, pore fluid chemistry, contamination level, and electric current (Yeung, 1994). EK remediation can be used for both saturated and unsaturated soils, but for better efficiency, the soil moisture content should be high enough to allow EM. Nonionic species would be transported along with the electroosmotically induced fluid flow. The efficiency of extraction relies on several factors such as species type, solubility, electrical charge, and concentration relative to other species (Mitchell, 1993). 

Figure 7 Evenly-spaced stylolites in the Salem Limestone of southern Indiana. Each stylolite is the seam of insoluble particles left by the stress-dissolution of a certain thickness of calcium carbonate. In contrast, in the region between any two adjacent stylolites, precipitation of calcite in pores has taken place rather than dissolution. A texture/pore-fluid chemistry feedback model has been proposed [ 19l to account for the generation of sets of stylolites in sedimentary rocks. Coin is 2 cm across.

To evaluate this hypothesis, experimentalists have been trying to provide data on mineral solubility and dissolution kinetics as a function of temperature, pH, and fluid composition. Experimental techniques and results of published studies are summarized below along with new data from our laboratory, including the results of pH-buffered, flow-through experiments that track variations in pore-fluid chemistry through time (Reed 1990 Reed and Hajash 1990, 1992 Franklin 1991 Franklin et al. 1990, 1991). 

These flow-through systems were used to investigate the dissolution of granitic sand (0.25-0.5 mm) in pH-buffered oxalic and acetic acids at 100 °C and 345 bar (Reed 1990 Reed and Hajash 1990, 1992). The reaction cell contained 180g of sand with an initial porosity of 46%. Pore-fluid chemistry was monitored through time to evaluate the potential ability of these fluids to dissolve aluminum and create secondary porosity. Experiments also examined whether organic components in solution could buffer the pH in systems with high surface area/fluid mass or if silicate hydrolysis reactions would dominate. 

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