Porosity preservation

Figure 8.34. Hypothetical porosity-depth curves for various diagenetic situations. A. "Normal" burial curve of chalk sequences. B. A typical curve stemming from porosity changes brought about by dissolution and cementation processes during meteoric zone diagenesis. C. A scenario for late stage porosity development brought about by a dissolution event related to hydrocarbon maturation and destruction. D. Porosity preservation resulting from conditions of overpressuring. (After Choquette and James, 1987.)...

Wagner P.D. and Matthews R.K. (1982) Porosity preservation in the upper Smackover (Jurassic) carbonate grainstone. Walker Creek field, Arkansas Response of Paleophreatic lenses to burial processes. J. Sediment. Petrol. 52, 3-18. 

Souza, R.S., De Ros, L.F. Morad, S. (1995) Dolomite diagenesis and porosity preservation in lithic reservoirs Carmopdlis Member, Sergipe-Alagoas Basin, northeastern Brazil. Bull. Am. Ass. petrol. Geol., 79, 725-748. 

Sandstones with potentially better porosity preservation are characterized by (i) coarser grain size and better sorting (ii) lower tendency to host extensive eogenetic carbonate cement than the finer sediments, which are more represented by well 34/4-1 samples and (iii) chlorite rims evolved from the infiltrated clay coatings, which are more abundant in coarse-grained sands which inhibited precipitation of pore-occluding quartz and carbonate cements. 

The patterns of diagenetic evolution recognized in this study allow discussion of the conditions for optimum porosity preservation and/or enhancement in the Serraria reservoirs. The best reservoirs of the unit occur in the Caioba area of the distal domain, where porosity was enhanced by dissolution of detrital feldspars and dolomite cement during telogenetic influx of meteoric waters. Similar conditions are expected for other structural blocks of the basin affected by post-rift uplift and erosion, or blocks bounded by major fault systems in which the Serraria Formation was relatively close to the... 

De Ros, L.F. (1990) Porosity preservation and generation in deep clastic reservoirs a review. Bol. Geoc. PETROBRAS, 4, 387-404 (in Portuguese with a summary in English). 

G. 2002. Porosity preservation in reservoir sandstones due to grain-coating illite a study of the Jurassic Garn Formation from the Kristin and Lavaran fields, offshore Mid-Norway. Marine and Petroleum Geology, 19, 767-781. 

Primary porosity The porosity preserved from some time between sediment deposition and the final rock-forming process (e.g., spaces between grains of sediment). 

The shaping of these fine, submicrometer powders into complex components and their subsequent consoHdation into dense ceramic parts of ideally zero porosity is a major technological challenge. The parts formed need to be consoHdated to near-net shape because Si N machining requires expensive diamond grinding. Additionally, Si N dissociates at or near the typical densiftcation temperatures used in the fabrication of stmctural ceramics and, therefore, special measures have to be taken to preserve the compositional integrity of the material. 

Besides the chemical composition, porosity is another property of stone which has great influence on its preservation. An increased porosity increases the exposed surface and pores allow movement of materials such as water and its solutes through the stones. If the pores are blocked or reduced in diameter such substances may be trapped within resulting in increased local interior damage. Exposure to the climatic elements is one important source of decay. Freeze-thaw cycles, in particular, result in pressures on the pore walls of the stone s interior from changes in volume during the phase transition... 

A large amount of water is added to the dehydrated material in order to cause it to swell the swollen structure is preserved when the material is frozen and subsequently dried in vacuo (in the frozen state) to a low moisture content. Some leaching occurs during the treatment with water and this, undoubtedly, further contributes to the increase in the porosity of the solid. Drying of the lyophilized substance can.be completed in a relatively short time in a vacuum oven at an elevated temperature, or at room temperature in the presence of an efficient water adsorbent. 

The previous sections have shown that desihcation of ZSM-5 zeohtes results in combined micro- and mesoporous materials with a high degree of tunable porosity and fuUy preserved Bronsted acidic properties. In contrast, dealumination hardly induces any mesoporosityin ZSM-5 zeolites, due to the relatively low concentration of framework aluminum that can be extracted, but obviously impacts on the acidic properties. Combination of both treatments enables an independent tailoring of the porous and acidic properties providing a refined flexibility in zeolite catalyst design. Indeed, desihcation followed by a steam treatment to induce dealumination creates mesoporous zeolites with extra-framework aluminum species providing Lewis acidic functions [56]. 

Compared to the in situ polymerisation of a monolith, the grafting approach does not need re-optimisation of the protocol in order to obtain an appropriate porosity and flow properties for the monolith when monomer or template is changed. Moreover, the properties of the core materials are generally preserved and the imprint generated on the surface of the materials only requires a minimum amount of template and provides well-accessible recognition sites. 

Lighty R.G. (1985) Preservation of internal reef porosity and diagenetic sealing of submerged ealy holocene Barrier Reef, southeast Florida Shelf. In Carbonate Cements (ed. O.P. Bricker), pp. 123-151. John Hopkins Press, Baltimore, MD. 

Surdam R.C. and Crossey L.J. (1985) Organic-rich reactions during progressive burial Key to porosity/permeability enchancement and/or preservation. Phil. Trans. Roy. Soc. London, Series A 315, 135-156. 

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