Salman Bloch, 1994. "Secondary Porosity in Sandstones: Significance, Origin, Relationship to Subaerial Unconformities, and Effect on Predrill Reservoir Quality Prediction", Reservoir Quality Assessment and Prediction in Clastic Rocks, Michael D. Wilson
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After two decades of research, secondary porosity remains one of the most controversial topics in clastic sedimentary petrology and reservoir quality assessment. Although the ubiquity of such porosity in sandstones of all ages worldwide is unquestionable, fumdamental disagreements remain as to its practical importance, origin, and effect on reservoir quality prediction.
It appears that the significance of secondary porosity and its impact on sandstone reservoir quality is frequently overemphasized. This can be attributed to two factors:
the subjective nature of the criteria used in defining and quantifying secondary porosity
the erroneous assumption that the presence of secondary porosity automatically results in a net increase of total porosity and permeability
A critical review of processes thought to be responsible for secondary proposity generation suggests that meteoric water influx provides the most effective leaching mechanism. Importantly, some of this porposity can be preseved during deeper burial, particularly in sandstones with high percentages of non-ductile grains. Silicate hydrolysis is probably the most important porosity-generating process in the deep subsurface. However, porosity created by this process is mostly “redistributional” (the volume increase produced by dissolution of minerals is counterbalanced by a similar volume decrease generated by precipitation of pore-filling diagenetic phases representing products of the dissolution reactions). The importance of organic acids as a quantitatively important porosity- enhancing medium is not clear.
The presence of secondary porosity does not appear to significantly affect the accuracy of empirical predictions in many sandstones for two reasons:
The extent of secondary porosity and permeability generation and
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Reservoir Quality Assessment and Prediction in Clastic Rocks
This course is designed to emphasize the following topics: (1) Historical perspective on previous and current empirical, and geochemical methods of reservoir quality prediction; (2) Overview of diagenetic processes which significantly impact reservoir quality and those factors which act as major controls on those processes; (3) Proper design of a comprehensive or limited-focus predictive analysis of reservoir quality; (4) Methodologies for the accurate measurement of all major dependent and independent variables; (5) Data analysis techniques involved in quality control and the assessment of variability prior to performing multivariate regression; (6) Steps involved in the generation of a multivariate regression to insure that the model developed provides maximum accuracy using a minimum number of independent variables; (7) Case histories from a variety of settings illustrating application of the recommended approach to reservoir quality prediction.