Intergranular volume

Burial carbonate cementation occurs subsequent to considerable compaction, leading to a successive decrease of both intergranular volume (IGV) and of 5 0 of the carbonate. However, in some basins, carbonate cementation may occur by ascending hot basinal brines to shallow depths (Sullivan et al.,... 

Fig. 16. Plot of intergranular volume (%) versus cement (%) for Lower and Middle Lunde sandstones with an intergranular volume 40% (see Houseknecht, 1987).

F, feldspar F total feldspar IGV, intergranular volume L, lithics P, plagioclase i quartz. 

An, Ca-plagioclase An ax composition of the most calcic plagioclase grain F, feldspar Fj, total feldspar IGV, intergranular volume L, lithics P, plagioclase Q, quartz Qp, polycrystalline quartz Qj, total quartz. 

Few fluid inclusion data have been published for calcite cement in shallow marine sandstones, and homogenization temperatures in calcite may possibly be reset (Barker Goldstein, 1990). However, the measurements reported by Saigal Bjorlykke (1987) are in the range 56-68 C and thus compatible with calcite precipitation prior to deep burial. Finally, the high intergranular volumes found in many calcite-cemented sandstone samples (Table 1) also indicate relatively early calcite precipitation. 

M. Cervarola, M. Modino and Macigno formations contain only small amounts of calcite cement, because intergranular volume (IGV) was reduced to <10% before cementation took place. 

Fig. 15. Intergranular volume versus calcite cement amounts in the Namorado Sandstone, based on the diagram of Houseknecht (1987)i...

Frag., fragments IGV, intergranular volume mono., monocrystalline poly., polycrystalline Qtz, quartz. 

Fig. 9. BSE image of a fine-grained, moderate to poorly sorted back-barrier marsh sample completely cemented by SI (white). Note the serrated nature of some quartz grains and the very high intergranular volume (>50%), which suggest the replacement of part of the margins of quartz grains by siderite cement. Sample F4-9441, Fly Lake 4, 2877.6 m. Scale bar = 500 pm.

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.

Paxton, S. T., Szabo, J. O., Ajdukiewicz, J. M. Klimentidis, R. E. 2002. Construction of an intergranular volume compaction curve for evaluating and predicting compaction and porosity loss in rigid-grain sandstone reservoirs. American ciation of Petroleum Geologists Bulletin, 86, 2047-2067. 

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-... 

It is usual for heavy concretes to have a certain structure. After selecting quantitative mixed proportions for producing dense packed coarse aggregates, the intergranular volume must be filled by cement-sand... 

The formation of carbonate cements typically preserves the intergranular volume (IGV) present at the time of cement formation with subsequent progressive burial, the IGV will be anomalously high. If the carbonate cement is later destabilized and the carbonate is dissolved, the sandstone will be characterized by enhanced porosity, a positive porosity anomaly. Enhanced porosity, or a positive porosity anomaly, is defined herein as porosity at a specific depth that is greater than the porosity predicted at that depth by a compaction/depth curve for the corresponding sandstone lithology (see Sclater and Christie 1980 Pittman and Larese 1991). 

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