Depositional and Diagenetic Evolution Related to Stratigraphic Sequence of Mauddud Formation in Halfaya and Ratawi Oilfields, Southern Iraq

Abstract

The present study analyzed microfacies, stratigraphic evolution, and diagenetic processes of the Mauddud Formation of Ratawi and Halfaya oilfields. Based on rock texture, component analysis, microfacies, and diagenetic features are determined through core, cuttings data, and well logs. Nine microfacies were identified, including Lime Mudstone, Benthic foraminifera wackestone, Peloidal wackestone, Bioclast packstone, Benthic foraminifera packstone, Algal packstone, Bioclast grainstone, Benthic foraminifera grainstone, and Peloidal grainstone. During the entire depositional period of the Mauddud Formation, local sea level fluctuation resulted in multiple transgressive and high-stand cycles, and the paleoenvironment changed from middle ramp) distal to proximal( to inner ramp shoal and middle ramp proximal to inner ramp shoal in single high stand cycle (HST). Inner ramp shoal to middle ramp proximal-distal in the single transgressive cycle (TST) developed during the local period. The most essential constructive diagenesis feature is dissolution, which frequently occurs alongside an HST cycle. Primary porosity and reservoir characteristics are reduced due to cementation and compaction. Dolomitization can also be viewed as a constructive diagenesis, as the dolomite produces intercrystalline pores that improve reservoir quality.