Sedimentology and reservoir characteristics of paleozoic Dibsiyah Member (Wajid sandstone), southwestern Saudi Arabia

Abstract

This study used multidisciplinary approach for examining the sedimentology and reservoir characteristics of the Dibsiyah Member. The Dibsiyah Member consists of varicolored rocks, mainly fine to coarse grained sandstones with intercalations of siltstones and conglomerates, exhibiting diverse sedimentary facies. Lower part of Dibsiyah Member is deposited in a braided stream within channel and bar subenvironments while the upper part is deposited in sandy shoreline of lower to upper shoreface sub-environments. The sandstone is classified as mature quartz arenite, highly enriched in quartz, but poor in feldspar, heavy minerals and lithic fragments. The XRD and SEM analyses also indicate predominance of quartz and sub-ordinate quantities of calcite, kaolinite and iron. Reservoir properties are affected by the diagenetic changes such as compaction, cementation, alteration and dissolution. Authigenic kaolinites coated the quartz grains, thus inhibit quartz overgrowth and thereby preserve the initial porosity and permeability. Statistical analysis indicates that porosity distributions are approximately normal and vertical as well as horizontal permeability distributions are positively skewed. The mean porosity and permeability values point to good reservoir qualities. The coefficient of variation shows the homogeneity of the porosity and heterogeneity of permeability distributions. Isoporosity and isopermeability maps revealed the distributions of the porosity and permeability within the outcrops of Dibsiyah Member.