Reservoir potential of the Haymana Formation submarine-fan sandstones in the Haymana Basin of Turkey

Sedimentological and petrographic studies of the Haymana Formation sandstones identify a submarine fan in the Haymana Basin. This study is confined to outcrop samples from the submarine-fan sandstones (the L1, L2, and L3 sections) and focuses on documentation of the petrographic characteristics of and depositional controls on reservoir properties of the Haymana Formation sandstones. Analysis of the lithology, texture, sedimentary structure, and petrography of the outcrop samples allows separation of the Haymana Formation sandstones into three distinct lithofacies, A, B, and C. Lithofacies A sandstones exhibit medium-coarse grain sizes (0.4–0.6 mm), moderate-good sorting, and subrounded grains. Lithofacies B sandstones exhibit fine grain sizes (0.2 mm), moderate sorting, and subrounded-subangular grains. Lithofacies C sandstones exhibit very fine grain sizes (0.112 mm) and nonreservoir facies. The main aim of this study is to document the diagenetic history and reservoir quality of the Haymana Formation sandstones. Lithofacies A has the best permeability, ranging from 80 to 120 mD, which can be related to the large grain size, the presence of cross-bedding, small amount of authigenic clays or cements in the pore throats, and enlarged pore apertures. In contrast, Lithofacies B sandstones contain variable yet small pore and pore-throat sizes, which are affected by abundant pore-filling authigenic clays, small grain sizes, and no dissolution. The permeability of the Lithofacies B sandstone ranges from 16 to 35 mD, which is lower than that of the Lithofacies A sandstone. Additionally, the Lithofacies B sandstones have small median pore-throat sizes (mean = 1.52 μm) and low porosities (average 4–6%), and the Lithofacies A sandstones have large pore-throat sizes (mean = 2.06–3 μm) and high porosities (average 20–25%), with most pore throats (50% or more) ranging between 1 and 4 μm. According to these data, the Lithofacies A sandstones show good reservoir characterisation. To date, significant hydrocarbon deposits have not been discovered in the Haymana Formation sandstones, although intensive exploratory work towards this end has been carried out in the Haymana Basin. According to this study, the proximal sandstones of the submarine-fan complex of the Haymana Formation may contain high-potential reservoirs in the Haymana Basin. In the basin, hydrocarbon is sourced from deep zones and may be capped by the proximal part of the Haymana Formation sandstones. According to this study, the Lithofacies B sandstones of the Haymana Formation are not suitable as diagenetic traps for hydrocarbon exploration in the Haymana Basin. However, the Lithofacies A sandstones may be expected to have the highest exploration success.