The subject of secondary porosity in sandstones received little attention in the published literature prior to 1975. Most workers considered only a very small portion of sandstone porosity to be of secondary origin. Except for fractures, most accounts of secondary porosity described outcropping sandstone formations where invading meteoric water had removed soluble constituents (Sedimentation Seminar, 1969; Hraber & Potter, 1969). Krynine (1941) indicated that leaching of carbonate in the Oriskany Sandstone may possibly have occurred in the subsurface. Proshlyakov (1960) was probably the first author
The reservoir aspects of fields producing from secondary-sandstone porosity are often more like those of carbonate reservoirs rather than those of fields with primary sandstone porosity. The distribution of secondary porosity in a prospective or productive sandstone formation may not necessarily show a direct relationship with depositional lithofacies or burial history and can be difficult or even impossible to predict with conventional subsurface methods. However, detailed geological and petrological analysis of the factors that control the occurrence of secondary porosity often greatly enhance the understanding and prediction of its distribution. Sandstone reservoirs with secondary porosity have special problems but they also offer special opportunities for both the explorationist and the exploitationist. It is necessary, firstly, to recognize the secondary nature of the porosity of these reservoirs; secondly, to interpret controls and timing of the origin of their porosity; thirdly, to evaluate any factors that may have played a role in preserving this porosity; and, fourthly to survey the existing pore geometry in order to optimize
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Secondary Reservoir Porosity in the Course of Sandstone Diagenesis
Secondary porosity n sandstones can be classified according to origin and pore texture. Five significant genetic classes of secondary porosity are defined by processes of origin: Fracturing; shrinkage; dissolution of sedimentary grains and matrix; dissolution of authigenic pore filling cement; and dissolution of authigenic replacive material. This publication provides information on the genetic-textural classes of secondary sandstone porosity; the textural spectrum of secondary sandstone porosity; the recognition of secondary sandstone porosity; the geological occurrence and diagenetic origin of secondary sandstone porosity; the textural stages of sandstone mesodiagenesis; the diagenesis of quartz arenites; the diagenesis of sandstones of intermediate and low mineralogical maturity; examples of porosity distribution, and reservoir aspects.