An integrated structural and stratigraphic characterization of the Apollonia carbonate reservoir, Abu El-Gharadig Basin, Western Desert, Egypt

Abstract

The current work aims to study the structural and facies characterizations of the Apollonia Formation carbonate reservoir by applying the curvature attribute and facies modeling. This reservoir is considered an unconventional, gas-bearing chalk reservoir located at the JDT field in the Abu El-Gharadig Basin, northern Western Desert of Egypt. The workflow begins by computing the curvature seismic attribute on the available 3D seismic data of the field. This is accompanied by the detailed sedimentological and petrophysical analysis of available core data and the distribution of the resulting facies log along the available 3D geological model. The results of the curvature attribute along the Apollonia “A5” layer showed faults traces more than three times the traces determined by the variance attribute along the same layer, with small horizontal spacing between faults about 230 m. This attribute is considered as the best attribute for determining subseismic resolution faults (SSRF) of the polygonal faults affecting the reservoir. The facies analysis indicated that this chalk reservoir is composed of four primary facie: Faceis A (clean chalk), Facies B (slightly argillaceous chalk), Facies C (argillacesou chalk) and Facies D (marl). These facies had been differentiated form each other based on the clay percentage, porosity and permeability. The best reservoir facies are Facies A (clean chalk) with a clay percentage 0–5%, average porosity 31% and average permeability 0.43mD and Facies B (slightly argillaceous chalk) with a clay percentages 5–15%, average porosity 23% and average permeability 0.12mD. Distributing these facies along the JDT field declares dramatically that facies characterization of the lower pay zone is better than the upper pay zone because of the abundance of A- and B-type facies along the lower zone. Consequently, a 3D geological model had been constructed which used for the determination of the best location of any further development well targeting primarily A- and B-type facies and for any future production and hydraulic fracturing operations.