Sedimentological control on the diagenesis and reservoir quality of tidal sandstones of the Upper Cape Hay Formation (Permian, Bonaparte Basin, Australia)

• Published in: Marine and petroleum geology Vol. 77; pp. 597 - 624
• Main Authors: Saïag, Jessica, Brigaud, Benjamin, Portier, Éric, Desaubliaux, Guy, Bucherie, Agathe, Miska, Serge, Pagel, Maurice
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-11-2016; Elsevier
• Subjects: Bonaparte Basin; Clay coating; Diagenesis; Earth Sciences; Permian; Petrography; Reservoir; Sandstone; Sciences of the Universe; Stratigraphy; Diagenesis; Petrography; Permian; Bonaparte Basin; Reservoir; Sandstone; Clay coating
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2016.07.002

The deep siliciclastic reservoir (>3500 m) of the Upper Cape Hay Formation of the Bonaparte Basin (Petrel gas field, Petrel sub-basin, Permian) exhibits wide heterogeneity in porosity (2–26%) and permeability (0.001–2500 mD). To investigate this variability, 42 samples were taken from five wells drilled through this formation. Six facies were identified from core descriptions and microscopic study of the sandstones. These facies are typical of a tide-dominated estuary, and include (1) mud flat, (2) sand flat, (3) top of tidal sand bar, (4) middle of tidal sand bar, (5) bottom of tidal sand bar, and (6) outer estuary facies. The paragenetic sequence comprises the emplacement of early aggregates of ferrous clay mineral precursors, mechanical compaction, recrystallization of those ferrous clay mineral precursors to Fe-rich chlorite and crystallization of Fe-rich chlorite forming coatings around detrital grains, chemical compaction, development of quartz overgrowth, feldspar alteration, crystallization of dickite and illite-rich illite/smectite (I-S) mixed layers, and ferrous calcite cementation. The middle and top of the tidal bars generally exhibit the highest porosity (Φ > 10%) and permeability values (k > 1 mD). Feldspar alteration released silica and aluminium into the reservoir promoting the development of dickite and illite-rich I/S mixed layers, which tended to destroy porosity and permeability, as calcite cements and quartz overgrowths. Diagenetic chlorite coatings around detrital grains are restricted to the sand bar facies deposited at the end of the last third-order transgressive systems tract of the Cape Hay Formation. The formation and conservation of ferrous clay precursors seems to be possible in an estuarine environment where seawater and fresh water are mixed and tidal sand bars are formed. These ferrous clay precursors recrystallized to Fe-rich chlorite coating after mechanical compaction. These coatings inhibited quartz cementation and prove to be the key parameter behind good reservoir qualities.
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•A sedimentary model of tidal sand bars in an estuarine environment is established.•Early aggregates of ferrous clay precursors were emplaced in tidal sand bar at the end of 3rd order transgressive cycle.•Chloritization occurs after mechanical compaction or at the beginning of the chemical compaction.•Cathodoluminescence microscopy and δ18O of quartz overgrowths indicate two silicification stages.•Chlorite coating preserves porosity and permeability.