Characterization of Upper Cretaceous Matulla and Wata clastic reservoirs from October field, Central Gulf of Suez, Egypt

Abstract

The objective of this study was to integrate petrographic thin sections, SEM, XRD, routine core analysis, gas chromatography, and wireline logs to present a comprehensive petrographic and petrophysical assessment of the shallow marine clastic reservoirs of the Coniacian-Santonian Matulla Formation and upper Turonian Wata Formation from the October field, Central Gulf of Suez Basin. The fine to very fine-grained glauconite-bearing subarkose quartz arenites of the Matulla and Wata reservoirs exhibit good intergranular primary porosity with good pore connectivity. Moderate to slight compaction and grain to grain pressure solution resulted in a slightly inhomogeneous packing of framework grains. Feldspar dissolution contributed to the secondary porosity which improved the reservoir quality, while quartz overgrowth and minor calcite cementation are inferred as porosity destroying diagenetic agents. Pore-filling kaolinite and clay phases also had a negative effect on reservoir storage capacity. Routine core analysis indicated > 20% porosity and up to 412 mD permeability in the meso-megaporous sandstones of both the reservoirs. Permeability anisotropy analysis of Matulla samples indicates the dominance of primary depositional fabric and isotropic pores with minor scattered/connected horizontal pores and vertical pore connectivity. Wireline log-based quantitative petrophysical assessments exhibit low shale volume and higher hydrocarbon saturation (up to 80%) on both the reservoirs, which is also supported by the gas chromatography data confirming the presence of oil in the Matulla, and Wata pay zones based on interpreted gas balance, wetness, and character ratios. The study concludes excellent reservoir properties in the Upper Cretaceous clastic intervals of the October field.