Reservoir characteristics and unconventional oil potential of Silurian aged Dadaş shale in southeast Turkey

Abstract

The early Silurian to the earliest Devonian Dadaş formation in the Diyarbakır Basin, Southeast Turkey, is characterized by mainly organic-rich shale. The Dadaş-I member is the early Silurian basal “hot shale” of the Dadaş formation, and is an important source rock for many reservoirs in the basin and might carry significant unconventional oil potential.Dadaş-I member is characterized and divided into four lithofacies (L1, L2, L3, and L4) by using lithological data from logs of 24 offset wells supported by the core data (porosity, permeability, saturation, pyrolysis, SEM and XRD data). Petrophysical properties of these lithofacies suggest that the hydrocarbon potential of L1 is not attractive, whereas those of L2 and L4 are quite attractive. Additionally, the hydrocarbon potential of the L3 is significantly low.We performed three methodologies to quantify the unconventional hydrocarbon potential of Dadaş-I formation: Log-Based, Core-Based, and Mathematical Modeling of basin history. For Log Based and Core Based (volumetric) methods, we calculate in-place hydrocarbon volume by using porosity, saturation, thickness and areal extension. Average saturations are obtained from logs for the Log Based method and from cores wherever available for the Core Based method.The Mathematical model conducts basin deposition modeling which is done for two wells, called Derindere-1 and Çalıktepe-2. The current depth and thickness values, conformity or unconformity at any point in the stratigraphic line up are history matched by using a software. The model iterates over sedimentation time, speed, and tectonic activity at the well and calculates pressure and temperature to which the target formation is exposed during the depositional history. The model eventually estimates and outputs the hydrocarbon volume generated, migrated, and remained within unit rock, which can be applied to the entire basin to estimate unconventional volumes.The calculated OIPs for Diyarbakır Basin are 74.16, 65.72 and 26.66 109 bbls for Log Based, Core Based, and Mathematical Basin Modeling methods, respectively. Here we consider the mathematical model result more of a lower limit, contrary, the log-based result might be considered as the upper limit for OIP potential.