The role of diagenesis at unconformities of the Paleozoic siliciclastic succession of central Saudi Arabia: implications for reservoir quality

Khalid Al-Ramadan*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

The aim of this paper is to elucidate the impact of unconformity surfaces on diagenetic alterations and their influence on reservoir quality evolution of the siliciclastic sequence. Samples were collected from the sandstones above and below two major unconformity surfaces in the Paleozoic successions of Saudi Arabia, including the Permo-Carboniferous Pre-Unayzah unconformity and the Ordovician Pre-Sarah unconformity. The main diagenetic alterations include the formation of kaolinite, calcite, and Fe-Ti oxide cements. The Pre-Unayzah unconformity shows an overall trend of increasing kaolinite towards the sequence boundary with severe dissolution of feldspar and mica which suggests a humid-wet climate that prevailed during the Permo-Carboniferous time. The general trend of increasing authigenic kaolinite abundance approaching the unconformity is observed for non-marine and marine successions. The reservoir quality of the overlying Unayzah Formation is negatively impacted by the occurrence of authigenic kaolinite owing to reduced porosity and permeability as well as causing potential “fines-migration” issues. The Ordovician Pre-Sarah unconformity, in contrast, shows no distinct trend in mineral leaching or kaolinite abundance which is consistent with the presumed cold-dry glacial environment during deposition of the Sarah sandstones. However, calcite- and ferruginous-cemented zones found along the Ordovician Pre-Sarah unconformity surface may act as localized seals for fluid flow within the sandstone. Such seals can adversely impact aquifer and reservoir compartmentalization. This study provides a better understanding of the vertical distribution, origin and timing of kaolinitization, and its impact to the prediction of reservoir quality along and below unconformities.

Original languageEnglish
Article number484
JournalArabian Journal of Geosciences
Volume14
Issue number6
DOIs
StatePublished - Mar 2021

Bibliographical note

Publisher Copyright:
© 2021, Saudi Society for Geosciences.

Keywords

  • Diagenesis
  • Kaolinite
  • Sandstones
  • Unconformity surface

ASJC Scopus subject areas

  • General Environmental Science
  • General Earth and Planetary Sciences

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