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Abstract

Litharenites and sublitharenites of the Devonian Lock Haven Formation contain abundant rock fragments of shale and phyllite. These labile grains suffered varying degrees of destruction in several depositional environments; hence, sedimentary processes largely controlled the sandstones’ mineral composition. Fluvial sandstones have a high lithic content, distributary mouth-bar and offshore-shelf sandstones have an intermediate content, and barrier-island sandstones have a low content.

Primary porosity relates inversely to compaction of the lithic grains, decreasing from a maximum minus-cement porosity of φmc = 33% down to zero as lithics increase. The majority of primary porosity, however, has been occluded by cementation. Secondary porosity, created chiefly by dissolution of the chemically unstable rock fragments, is greatest (φrf = 13%) for sand-stones of a moderate lithic content.

Because of these relationships among depositional processes, lithology, and porosity, we predict that sandstones of different sedimentary environments should exhibit distinct porosity volumes and vary in their reservoir potential. Mouth-bar sandstones will have good total porosity, good secondary porosity, and offer the best reservoir quality. Shelf sandstones will have fair total porosity, most of which is secondary, whereas beach sand-stones will have low total porosity, most of which is primary. Fluvial sandstones will be the poorest reservoirs.

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