Sedimentology and geochemistry of Zubair Formation sandstone reservoir, East Baghdad Oilfield, central Iraq

Abstract

Two wells (EB10 and EB92) within the East Baghdad Oilfields in central Iraq were chosen to study the Zubair Formation sandstones. The Zubair sandstones mostly consist of quartz (84–97.5%), feldspar (0–2.9%), and heavy minerals (0.1–1%) with a few rock fragments. The most common binding materials are silica, carbonate, and ferruginous cements. As a result, matrix makes up less than 10% of the rock. The sandstones are mineralogically and texturally mature quartz arenites. Heavy minerals were classified into four major groups. The opaque, ultrastable (zircon, tourmaline, rutile), metastable (pyroxene, amphibole, garnet, epidote), and mica (muscovite, biotite, chlorite) groups are among these as well. These minerals' features revealed that they are mostly of mature passive continental margin, acidic igneous, and regional metamorphic origin. The Arabian Shield is thought to be the origin of the Zubair sediments, which were deposited under humid or tropical conditions. Zubair Formation sandstones are medium to very fine and well to moderately well sorted sediments. Sedimentary structures and grain-size parameters propose that the Zubair sandstones formed in a mixed fluvial, beach, and shallow marine environment. Sandstone geochemistry has been investigated in order to infer provenance and tectonic settings by subjecting them to whole rock geochemistry (major oxides, trace). The results show that the major oxides of the Zubair sandstones vary only slightly with depth. In comparison to PAAS and UCC values, SiO2 is enriched, while Al2O3, CaO, MgO, Na2O, and K2O are depleted. The geochemical indices of the sediments clearly imply that they were deposited in a humid, non-marine environment.