Estimation of oil in-place resources in the lower Oligocene Mezardere Shale, Thrace Basin, Turkey

Abstract

Abstract Tertiary Thrace Basin of northwestern Turkey contains Early/Middle Eocene through Pleistocene age sediments the thickness of which reaches up to 9000 m in its depocenter. In this time interval, the Mezardere Formation was deposited in the Early Oligocene (36 m.y.) through Middle Oligocene (30 m.y.). Mezardere Formation is characterized by thick marine-prodelta organic rich shales, marls and sandstones. Present and previous research results showed that the Mezardere Shale contains marine Type II+III kerogen (HI=3–744 mg HC/g TOC) and sufficient organic richness (TOC=0.08–3.39 wt%) and has favorable thermal maturity (%VRm=0.35–1.20) in order to generate oil, condensate as well as wet-gas. Furthermore, discoveries of conventional oil, condensate and wet-gas and correlation of these fluids with the Mezardere Shale gives us a confidence that Mezardere Shale may retain hydrocarbon fluids and could be a significant shale-oil play in the Thrace Basin. Hence, the aim of this study is to estimate oil in-place (OIP) resource volume in the Mezardere Shale. For this purpose, available Rock-Eval data acquired from 407 Mezardere Shale cuttings and core samples from 47 wells are studied and evaluated. Five out of 47 wells show relatively continuous “Oil Saturation Index, (OSI=S1/TOC*100”) values. It is crucial to note that measured S1 and therefore OSI values are corrected against the evaporation loss. Corrections are made for 35, 40, and 45 API oils which are assumed to be present in the Mezardere Shale as retained oil. OIP resource estimations are conducted for the five wells as well as for the determined core area (e.g., 1000 km2 in the northwestern Thrace Basin). An average Mean Swanson's value of OIP's of the five wells is estimated to be approximately 405 M bbl. The core area shows an average Mean Swanson's value of OIP as 325 MM bbl.