A Theory of Framework Grain Dissolution in Sandstones
Framework grain dissolution (FGD) involving feldspars and rock fragments was found to be significant to reservoir properties in sandstones with more than 10% soluble grains. FGD porosity ranged up to approximately 70% and averages about 30% of the visible porosity in a study of some reservoir sandstones. FGD does not appreciably increase reservoir permeability. However, the amount of FGD porosity developed was found to be a function of the sandstone’s initial permeability.
We propose that clay and organic maturation in shales produce the necessary water, acid, and complexing agents for FGD. The FGD solvent is expelled into the sandstones where feldspars and rock fragments are dissolved, and the resulting aqueous aluminum is complexed for transport out of the sandstone.
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Clastic diagenesis has evolved from a very descriptive science to a much more process-oriented study. This evolution has been driven by the realization that many hydrocarbon reservoirs have significant diagenetic compotents directly affecting porosity and permeability characteristics. The prediction in time and space of reservoir characteristics affected by diagenesis can greatly reduce the risk in the search for hydrocarbon accumulations, particularly in subtle targets lacking pronounced structural expression. This publication contains three sections designed to increase understanding in the processes controlling clastic diagenesis: Conepts and Principles; Aspects of Porosity Modification; and Applications of Clastic Diagenesis in Exploration and Production. The first two sections deal with processes controlling various aspects of clastic diagenesis, and the third section applies these principles and observations to specific examples. Altogether, the three sections contain 22 chapters.