Dissolution fronts

WIPP is located 26 mi east of Carlsbad, New Mexico. Other features of interest to site selection shown on this map are the salt dissolution front and the 1976 location on the potash leasing area. 

Keywords Porous media, precipitation, dissolution, fronts, upscaling... 

Dissolution fronts. Assuming u < u at the inlet x 0 and v t=o vq > 0 on the side walls, a dissolution front occurs after a waiting time that can be computed explicitly. 

Knabner, P, van Duijn, C.J. and Hengst, S. (1995) An analysis of crystal dissolution fronts in flows through porous media. Part 1 Compatible boundary conditions, Adv. Water Res. 18, 171-185... 

For macropores in a stable growth condition, the distribution of current density on the surface of an individual pore bottom is bell-like and is constant with increasing depth as shown in Fig. 8.70(a). For micro PS, the pores tend to grow in a randomly fashion. The distribution of the current at the dissolution front of the PS is highly modulated across the surface as illustrated in Fig. 8.70(b). The distribution changes with time but at any given time there are areas on which the current is near zero (e.g. on the walls). 

B) Boundary between calcite-cemented and uncemented horizons in Avalon Sandstone, showing no evidence of dissolution. Straight crystal faces of the poikilotopic calcite (left) at the boundary (centre) indicate the presence of a cementation front, rather than a dissolution front. Note that framework grains in the porous zone are coated with thin clay rims, which are absent in the cemented zone. The former is also slightly more compacted than the latter. Same locality as... 

In soluble rocks the effect of flow is shown in formation of zones with drastic decrease in rock permeability in the direction of flow. Such zones are called dissolution fronts. Permeability change in rocks causes increase in hydrostatic head and the formation of ascending sources. 

The size of the cathodic region preceding the anodic dissolution front depends on the structure of the interface and the... 

Morphology of Dealloyed Structures on 2-D Lattices The roughness of the dissolution front is characterized by its fractal dimension, d (estimated from the mass theorem [190]). Variation of as a function of p is shown in Figure 31, displaying the classical transition toward the dimension of the infinite cluster at the percolation threshold d = 1.60). 

Easier diffusion of B produces features such as a smoother dissolution front, internal vacancy clusters (polyatomic voids), and islands of A-type atoms hindered from dissolution. Qualitatively similar conclusions are drawn on 3D lattices except for the specific generation of pores with easier diffusion of B atoms as predicted [201 ] by a nonstochastic approach. This tendency to generate a tunneling attack at the cost of only surface diffusion could be considered as a likely explanation of pit nucleation at the atomic level, with no need for the concept of passive film breakdown. 

Figure 31. The fractal dimension d of the dissolution front as a function of p. For the 2-D rule (line 1 in Table 2). From ref [32],...

The predictions for reactions of quartz with the young fluid indicated that by end of the experiment quartz would be completely dissolved in the first half of the column, with a very sharp dissolution front. It was predicted that tobermorite would precipitate at the dissolution front, with foshagite precipitating behind the dissolution front replacing the quartz. Only small quantities of the CSH phases were predicted, together with an increase in porosity. Additionally, Ca(OH)2 was predicted to precipitate at the... 

Predictions involving the reaction of quartz with the evolved fluid (Fig. 7) indicated dissolution was slower compared to the simulation with the young fluid. The dissolution front was predicted to be very sharp but to reach only a few centimetres into the column. Large quantities of CSH phases were predicted to precipitate, with an associated reduction in the porosity of the column. 

The predictions for the muscovite/quartz mixture reacting with the young fluid showed quartz dissolving quickly. The quartz dissolution front was predicted to be sharp and appeared to be associated with a brief period of zeolite precipitation. The muscovite dissolution front was also predicted to be sharp. However, the muscovite took longer than the quartz to dissolve. A region of muscovite precipitation in front of the dissolution front was predicted. 

Tobermorite was predicted to form at the dissolution front together with the zeolite phase, mesolite. Foshagite was predicted to precipitate behind the dissolution front. There was a predicted increase in porosity for the entire column. At short timescales, a sharp decrease in porosity was predicted, associated with the zeolite precipitation at the quartz dissolution front. This disappeared over longer timescales following removal of quartz from the column. In the first 100 mm of the column, there was predicted to be a large increase in porosity corresponding to the muscovite dissolution front. For the remainder of the column, there was also a predicted increase in porosity but this was minor by comparison. 

As with the quartz column modelling, it was predicted that the reaction of the muscovite/ quartz mixture with the evolved fluid would produce larger amounts of the secondary phases than with the young fluid. The predicted development of porosity was complex, over the first 150-180 mm of the column a reduction in the porosity was predicted, as a result of secondary phase precipitation. Then there was a short length of column where there was an increase in porosity. This appeared to correlate with the quartz dissolution front. 

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