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

Abstract

This study discusses the petrographic and petrophysical characteristics of the shallow marine clastic reservoirs of the Coniacian-Santonian Matulla Formation and upper Turonian Wata Formation from the October oil field, Central Gulf of Suez Basin. Thin sections, SEM and XRD data indicate that the studied glauconitic subarkose quartz arenites of the Matulla and Wata reservoirs are fine to very fine-grained, moderately sorted, subrounded to subangular and 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 generation which enhanced 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 average > 20% porosity and good permeability (up to 412 mD) 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 assessments provided quantitative petrophysical properties which also exhibit low shale volume and higher hydrocarbon saturation (up to 80%). The same has also been deciphered from the gas chromatography data which confirms the presence of oil in the Matulla and Wata pay zones based on gas balance, wetness and character ratios. The study concludes excellent reservoir properties in the Upper Cretaceous clastic intervals of the October field.