Porosity intergranular

The typical value of porosity for a clean, consolidated, and reasonably uniform sand is 20%. The carbonate rocks (limestone and dolomite) normally exhibit lower values, e.g., 6-8%. These are approximate values and do not fit all situations. The principal factors that complicate intergranular porosity magnitudes are uniformity of grain size, degree of cementation, packing of the grains, and particle shape. 

The size and volume of the intergranular porosity decreased with the increase of the coordination number among grains with pressure. 

It was assumed that intergranular porosity m for grain fraction with narrow intervals did not change during granulation and was constant for a given raw material ... 

Void spaces generated by the assembly of grains (crystals micellae aggregates, etc.) which define the intergranular porosity. 

Jaegerskou, A. Holm, P. Schxfer, T. Kristensen, H.G. Granulation in high speed mixers. Part HI effects of process variables on intergranular porosity. Pharm. Ind. 1984, 46, 310-314. 

Fig. 14. Intergranular volume (IGV) versus total cement for Norphlet sandstones from Mobile Bay. The diagonal lines represent intergranular porosity. The majority of samples plot in the shaded area representing IGV < 26%, indicating that intergranular pressure solution has played a significant role in reducing IGV.

Intergranular porosity is the dominant pore type observed in thin sections from the cores examined in this study. The amount of porosity that can be attributed to dissolution of framework grains in the Norphlet is volumetrically insignificant (Table 2). Although partial dissolution of early anhydrite is noted, no evidence for dissolution of significant volumes of pore filling cements was found in this study. 

Fig. 19. Results of compaction and quartz cementation models calculated using quantitative petrographic data, Touchstone and the thermal history shown in Figure 16. (a) Calculated versus observed IGV 4% tolerance, (b) Calculated versus observed quartz cement volume 3% tolerance, (c) Calculated versus observed intergranular porosity 4% tolerance.

We shall now propose an approach for the evaluation, in the Saharan reservoirs, of the relative importance of the process of compaction and cementation in the reduction of porosity by presenting correlation plots of intergranular volume (VIG) vs. cement (Fig. 4.16). It is generally held that under the conditions of sediment accumulation on surface the VIG of well-graded sandstones is about 40%. This VIG or porosity can only be reduced by compaction, a mechanical process reducing VIG to 30%. Any further reduction by chemical compaction or pressure solution is a specially important process. The intergranular porosity of a sandstone is a function of the volume preserved after compaction and of its (the VIG s) portion filled by cement (Fig. 4.16). The inter-... 

Fig. 4.46. Dependence of the initial permeability on average grain size in YIG intergranular porosity values are indicated (Globus Duplex, 1966).

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