Petrography and authigenic chlorite in the Siegenian reservoir rocks, Berkine Basin, eastern Algerian Sahara
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ORIGINAL PAPER
Petrography and authigenic chlorite in the Siegenian reservoir rocks, Berkine Basin, eastern Algerian Sahara Sid Ahmed Ali Khoudja 1 & Smaine Chellat 2 & Messaoud Hacini 1 & Abdelkader Semiani 3 Received: 3 January 2020 / Accepted: 29 July 2020 # Saudi Society for Geosciences 2020
Abstract In Berkine Basin, the Siegenian stage is constituted by clayey sandstones and it contains several reservoir levels especially in the perimeter of Zemlet El Arbi, where the sandstone levels can reach 30 m of thickness. The Siegenian reservoir shows a tidal deposit environment, it is located at depths greater than 3200 m, its average thickness is 200 m in the south and it decreases to 30 m because it is strongly affected by Hercynian orogeny mainly in the northwest of the studied area. Petrographic and X-ray diffraction studies indicate the presence of authigenic chlorite, which is the most important cement in Siegenian sandstones. Chlorite appears in different forms: grain coating, pore lining, pore filling and rarely in the form of oolite. It often has a great impact on petrophysical reservoir qualities by inhibiting authigenic quartz overgrowth in porous space and preserving porosity. Other diagenetic phenomena observed are mechanical compaction, alteration and dissolution of feldspars and biotite, precipitation of clay minerals (smectite, berthierine, chlorite, kaolinite and illite) and precipitation of secondary silica, carbonates, pyrite and haematite. Keywords Berkine . Petrography . Diagenesis . Chlorite . Siegenian . Petrophysics
Introduction The process of diagenesis is a compaction criterion for sediments; theoretically, diagenesis includes a broad spectrum of physical, chemical and biological processes after sediment deposition, where sedimentary assemblage and interstitial water are reacted to achieve a textural and Responsible Editor: Domenico M. Doronzo * Sid Ahmed Ali Khoudja [email protected] Smaine Chellat [email protected] Messaoud Hacini [email protected] Abdelkader Semiani [email protected] 1
Laboratoire de géologie du Sahara, Université Kasdi Merbah, 30 000 Ouargla, Algeria
2
Laboratoire de géologie et d’environnement, Université Constantine 1, Route Ain El Bey Zouaghi slimane, 25 000 Constantine, Algeria
3
Division Exploration Sonatrach, Avenue du 1er novembre, 35000 Boumerdes, Algeria
geochemical equilibrium with their environment (Curtis 1977; Burley et al. 1985; Larsen and Chilingar 1979; Brand et al. 1998; Mcllreath and Morrow 1990; Fowler and Yang 2003). Diagenesis can be considered all phenomena that contribute to the transformation of sediments into sedimentary rock from erosion to metamorphism during burial (Worden and Burley 2003; Larsen and Chilingar 1979; Brand et al. 1998; Mcllreath and Morrow 1990; Fowler and Yang 2003). Diagenesis is generally associated with secondary mineralisation, which is related to compressive or extensive tectonic phases. Chlorite is considered a postsedimentary mineral and has been studied by several authors (Odin 1990; Pittman and Lumsd
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