Reservoir Quality with Integrated Well Logs, Petrography, and Petrophysical Parameters of the Çağlayan Formation Sandstones around Ereğli-Amasra in the Western Black Sea Region, Turkey

ABSTRACT In the present study, the subsurface data are used to determine the reservoir quality of the Lower Cretaceous-aged sandstones of the Çağlayan Formation in wells drilled in the Ereğli and Amasra regions. Well logs, petrography, and petrophysical analyses were used for reservoir characterisation. The Çağlayan Formation sandstones are divided into three lithofacies (A, B, and C) according to their lithology, texture, and petrographic features. The effective porosities varied between 29-37% and 23-29% in lithofacies A and B, respectively. Similarly, the average permeability values varied between 16-74 and 78-316 mD for lithofacies B and A, respectively. As a result of log values, the sandstones of the Çağlayan Formation around Ereğli-Amasra are good to excellent quality reservoir rocks. However, log porosity values are thought to be higher than expected due to bed boundary formation. The core porosities (effective) varied between 5-17% and 1-4% in Lithofacies A and B, respectively. Similarly, the average permeability values varied in the range of 0.3-4 and 4-7 mD for Lithofacies B and A, respectively. The Porosity values are fair to good, while the permeability values are poor. Illite and Kaolinite negatively impact reservoir permeability by their clay structures and abundance. The capillary pressure curves of the Lithofacies A sandstones of the Çağlayan Formation are parallel to the x-axis, and are weakly parallel to the x-axis in Lithofacies B sandstones. Although lithofacies A sandstones of the Çağlayan Formation show good reservoir characterisation, lithofacies B sandstones show intermediate reservoir characterisation. Sandstones of the Çağlayan Formation are expected to have intermediate- good reservoir potential.