Formation of secondary porosity in sandstones by quartz framework grain dissolution

Abstract

An understanding of the nature and origin of porosity in sandstones is crucial to the evaluation of their potential as hydrocarbon reservoirs. Primary porosity is normally destroyed by cementation, compaction and pressure solution during burial, but it has recently been recognized that significant secondary porosity can develop at depth^1–3. This discovery has been called “the most significant advance in the study of clastic diagenesis in the past decade”⁴. Several genetic types of secondary porosity have been identified ; these include porosity formed by: (1) fracturing; (2) shrinkage; (3) dissolution of sedimentary grains and matrix; (4) dissolution of authigenic cements; and (5) dissolution of authigenic replacive minerals⁵. Formation of secondary porosity by framework grain dissolution has been thought mainly to involve decomposition of feldspars and lithic grains^6,7.We demonstrate here that significant secondary porosity can also develop by dissolution of quartz framework grains if the rocks are exposed to alkaline pore fluids during deep burial and/or uplift.