Abstract
In this study, a sandstone interval of the lower Cretaceous successions in SW Iran is analyzed regarding the effects of late diagenesis on the alteration of primary reservoir quality and pore system. Petrological and geochemical analyses indicate dominant quartz mineralogy (quartz arenite) deposited in distributary channel and mouth bar environments which is embedded in delta front to prodelta argillaceous sediments. Rather than mineralogy and some remaining primary (intergranular) porosity, several late (burial) diagenetic processes including multi-phase carbonate cementation, chlorite cementation, and chemical compaction, affected the reservoir quality. Most of the diagenetic processes had a decreasing effect on the primary reservoir quality. All recognized diagenetic features are related to burial diagenesis of the surrounding open marine shales (clay mineral transformation) and expelled diagenetic fluids.
Highlights
Siliciclastic rocks have lower diagenetic sensitivity and heterogeneity in comparison with carbonates (e.g., Ebanks et al 1992; Slatt and Galloway 1992; Lucia 2007; Ahr 2008; Burrowes et al 2010)
The main aspect of this study is evaluating the role of burial diagenesis in the alteration of primary reservoir quality and homogeneity, regarding the very low preliminary diagenetic potential of the studied interval
After physical compaction, dissolution of quartz grains, calcite cementation and replacement, and chlorite cementation (Fig. 6i, j) took place contemporaneously which could be related to a series of reactions which release H+ and Ca2+ ions and CO2 (Fig. 11)
Summary
Siliciclastic rocks have lower diagenetic sensitivity and heterogeneity in comparison with carbonates (e.g., Ebanks et al 1992; Slatt and Galloway 1992; Lucia 2007; Ahr 2008; Burrowes et al 2010). In siliciclastic (reservoir) rocks, diagenetic processes are well studied (e.g., Pettijohn et al 1987; Morad et al 2012) but their relationships and development mechanisms can be different and crucial in reservoir characterization. A clean and quartz-rich sandstone (quartz arenite) has a low diagenetic potential and is basically prone to cementation (quartz and carbonate) and compaction (e.g., Pettijohn et al 1987; Moore 2001). High degrees of diagenetic modification and cementation as the main characteristics of this thin unit led to a heterogeneously distributed reservoir and non-reservoir intervals despite its depositional homogeneity and high primary intergranular porosity. The main aspect of this study is evaluating the role of burial diagenesis in the alteration of primary reservoir quality and homogeneity, regarding the very low preliminary diagenetic potential of the studied interval
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