Güneydoğu Anadolu Bölgesi Dadaş Formasyonu’nun Organik ve İnorganik Jeokimyasal Özellikleri

Abstract

Shale oil and shale gas reservoirs have become an important energy source all over the world. Dadas Formation has a double role as source rock and reservoir rock in recent studies. Outcrop and well samples (cuttings and core) were taken from formation at five locations in around Çat, Çermik/Korudağ, Diyarbakır and Bismil. The mineralogical compositon of shales is clay, quartz, mica and feldspar minerals and small amounts dolomite, calcite and pyrite minerals. The predominant lithology in shales identified to have detrital texture according to thin section studies is clay-rich siliceous mudstone, silica-rich clayey mudstone and mixed argillaceous mudstone. XRD clay diffraction analysis shows that samples mainly contain illite, kaolinite and minor chlorite. According to Illite crystallinity (ICCIS), Sharpness Ratio (SR) and Chlorite crystallinity (ChC) values, the samples are in “early diagenetic zone-low anchizone” and “onset of metamorphism”. Brittleness index (BI), Young’s/Elastic Modulus (EK) and Hardness (HK) values of the Dadaş Formation vary between 28-56%, 40-56 GPa and 0.85-2.28 GPa, respectively, and the highest values were determined in Çat ÖSK. Dadaş Formation has a economic shale oil and shale gas potential with Total Organic Carbon (TOC) content between 0.73% and 7.51%. Rock-Eval pyrolysis analysis results show that surface samples are found in “Type IV and gas window” where hydrocarbon conversion occurs at a high rate (TR, 92.41-99.58%), while well samples are located in “Type II kerogen and oil window”. The mineral matrix effect causing lower values than present day HI (mg HC/g TOC) values were evaluated by regression equation of S2 and TOC content and SEM-EDAX analysis in graptolite periderm. The results detected in graptolite periderm with C, O associated with the mineral matrix the element Al, Si, Mg, Ca, Fe, S elements are determined. As the thermal maturity of shale decreases, the percentage of C element (up to 86.63%) increases and there is a considerable decrease in the amount of elements associated with the matrix. Organic material components of Dadaş Formation; amorf organic matter (AOM), palynomorphs and zooclasts. The graptolites observed in the samples are Aronian-Telychian represents the age range. Palinomorphs indicate the Late Ruddanian-Early Venlock depositional age of the formation. Both granular and non-granular graptolite morphology has been detected in Dadaş Formation. The bireflection and random values of graptolite reflectance (GR) range from 0.72% to 2.59% (VREgr≈0.69-2.05%), indicating thermal maturity between the “oil window” and the “dry gas window”. The calculated VRETmax values were found to be higher (2.01-3.28%) than VREgr values due to low S2 values in surface samples. Raman spectroscopy of graptolites D band values (1350.46-1358.76 cm-1) have a negative correlation with thermal maturity level. On the other hand, G-D band separation and %GR values have a positive correlation. MCIP, Rock-Eval based organic porosity (Øorg), SEM and FIB-SEM analyzed were performed on Dadaş Formation with different thermal maturity. According to the MCIP results, the pore diameter of the samples varies between 3 nm-10 µm and the mesopore is dominant. Øorg values were calculated with Rock-Eval pyrolysis parameters, as the percentage in kerogen and shale. While Øorg values are between 5.26% and 35.71% on average in kerogen, in shale varies between 0.28% and 1.18%. Øorg values increase as thermal maturity increases. The dominant pore type are interP pores determined via SEM and FIB-SEM analysis. According to all analysis results obtained from the samples taken in this study, Dadaş Formation is grouped from northwest to southeast in the region as overmature, mature and early mature and intraP organic matter pores were observed in each thermal maturity. As a result, well samples based on OSI values could possibly have shale oil potential and outcrop samples may have shale gas potential with %VRE values. The results obtained in this study will contribute to the understanding and evaluation of the unconventional resource characteristics of Dadaş Formation.