EXPLORING UNDER THE OPHIOLITE

The oil province of the SE Turkey Basin is widely viewed as a mature area for exploration activities, with many of the more significant discoveries (e.g. Beykan, Kurkan, Raman, Garzan) being made more than 30 years ago. Since acquiring Shell’s assets in 1996, Perenco have managed to maintain a steady production of ca. 12,000bopd in the area whilst devising an exploration strategy to replace and replenish these fields once decline sets in. In 2006 a regional play fairway analysis was conducted incorporating all available well, seismic and published data which resulted in the identification of four themes deemed as having the potential to deliver moderate to company impact exploration opportunities. One of these themes detailed the possible northerly extension of the Cretaceous, Devonian and Ordovician plays away from the WSW – ENE trending proven oil field area (Beykan – Katin) into the more internal parts of the Taurus fold and thrust belt that developed due to the closure and over-thrusting on the southern Tethyan margin. Offset wells on trend to the south west and east of this area of interest suggest the potential for a thick pre-Tertiary sequence, sampling the Cretaceous Mardin Group, and in specific areas the unconformably underlying Devonian Hazro and Ordovician Bedinan Formations. Oil and gas shows are common throughout the sequence. The world-class Silurian Dadas Shale source rock is thought to be present and oil seepages in the area indicate the presence of a working petroleum system. In 2008 Perenco were awarded the ‘Dicle’ (4474) license 100% and have subsequently been awarded (June 2010) the ‘Dicle East’ licenses in a partnership with TPAO. Exploration studies to date have included geological fieldwork, structural, sedimentological and geochemical modelling, along with reconnaissance 2D seismic acquisition. The focus of this paper will be the exploration potential of the Dicle License area. In Dicle, surface geological outcrops are dominated by broadly east-west trending 4-way dip closed surface anticlines. These features are well defined by outcropping Eocene-aged Midyat limestones and dolomites, which where buried under an appropriate thickness of overburden, can form excellent reservoirs (e.g. Selmo field). Further north and to the south-west (e.g. Abdulazziz Anticline) erosion into these features reveals the presence of a thick ophiolitic group comprising the Hezan (Jurassic-Triassic aged carbonates) and Karadut (indeterminate aged melange of mudstones and fine-grained clastics) Formations. From close offset well data these ophiolitic units are seen to be part of an allochthonous nappe encompassed by the Maastrichtian-aged Kastel Formation (mudstones, siltstones and marls), which conformably overlie the Campanian Sayindere and Karabogaz Formations underneath which the Mardin Group is found. By projecting 40km northwards from the well explored oil field area we expect the Silurian Dadas shale and the Devonian Hazro sandstones and carbonates to subcrop the base Cretaceous unconformity from west to east. A series of structural cross sections honouring both field geological measurements and the recently acquired 2D seismic are presented which suggest sub-surface traps bearing carbonate and clastic reservoirs from the Cretaceous, Devonian and Ordovician. Burial history and 1D geochemical modelling also presented here indicates that the primary source rock interval, the Silurian Dadas Shale has potentially generated significant quantities of both oil and gas in the area. In 2011 Perenco intend to drill exploration wells in both Dicle and Dicle East to test the source, reservoir and seal play elements below the ophiolitic allochthonous nappe.