Terrigenous sandstones in many basins owe their reservoir quality to secondary porosity that developed by the dissolution of detrital framework grains (chiefly plagioclase, carbonate rock fragments, and unstable heavy minerals), carbonate fossil fragments, and cement minerals (chiefly calcite and evaporite minerals). This dissolution event is responsible for changing tight sandstones to porous and permeable sandstones slightly prior to the major episode of hydrocarbon migration. Dissolution of most non-evaporite minerals is accomplished by formation water containing carbon dioxide generated during the thermal or bacterial breakdown of hydrocarbons. Dissolution porosity is commonly well developed at 6,000 to 9,000 ft (1,828 to 2,743 m), but gradually is lost during deeper urial stages by recementation (chiefly by ferroan calcite, ferroan dolomite, and kaolinite). Variations in the simple scheme during sandstone burial of cementation^rarrdecementation^rarrrecementation is complicated in basins with complex "plumbing" systems and those that experience uplift. For example, dissolution porosity in some uplifted sandstones develops during invasion by meteoric water flowing downdip.

Dissolution porosity in sandstones can be suspected from certain log responses and water saturation characteristics, but is best identified from clues visible in thin sections made of dyed epoxy-impregnated perm plugs. Clues to secondary porosity in thin section include: (1) oversize pores formed where framework grains have been dissolved, (2) patchy distribution of carbonate or evaporite cement, (3) honeycombed feldspar grains, (4) fossil molds, (5) corroded grains whose margins were etched by previous cement, (6) broken silicate framework grains that formed when rapid compaction followed removal of cement minerals, and (7) quartz grains that have been reduced to a pile of shards when calcite, which invaded quartz along hairline fractures during cementation, was dissolved.

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