BIOMARKER GEOCHEMISTRY OF CRUDE OILS AND NEOGENE BITUMINOUS SHALES IN THE YENIKoY AREA, EREGLI-ULUKISLA BASIN, CENTRAL ANATOLIA, TURKEY


Kara-Gulbay R. , Korkmaz S., Erdogan M. S. , Kadinkiz G.

JOURNAL OF PETROLEUM GEOLOGY, cilt.42, ss.173-191, 2019 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 42 Konu: 2
  • Basım Tarihi: 2019
  • Doi Numarası: 10.1111/jpg.12729
  • Dergi Adı: JOURNAL OF PETROLEUM GEOLOGY
  • Sayfa Sayıları: ss.173-191

Özet

In the Eregli-Ulukisla Basin, southern Turkey, crude oil shows have been observed in the subsurface in the shale-dominated non-marine Upper Miocene - Pliocene succession. Based on analyses of samples from four boreholes, the shales' organic matter content, thermal maturity and depositional characteristics are discussed in this study. Geochemical correlations are established between shale extracts and a crude oil sampled from the shale succession. The shales have moderate to high hydrogen index (HI) and very low oxygen index (OI) values. Pyrolysis data show that the shales contain both Types I and II kerogen, and n-alkane and biomarker distributions indicate that organic matter is dominated by algal material. Very high C-26/C-25 and C-24/C-23, and low C-22/C-21 tricyclic terpane ratios and C-31 R/C-30 hopane, C-29/(C-28+C-29) MA and DBT/P ratios in shale extracts indicate that deposition occurred in a lacustrine setting. High gammacerane and C-35 homohopane concentrations and low diasterane/sterane ratios with a very low Pr/Ph ratio suggest that both the shales and the source rocks for the oil were deposited in a highly anoxic environment in which the water column may have been thermally stratified. Although the shales analysed have very low T-max values, the production index is quite high which suggests that the shales are early-mature to mature. Biomarker ratios including C-32 22S/(22R+22S) homohopanes, C-29 20S/(20R+20S) and beta beta(beta beta+alpha alpha) steranes, moretane/hopane, TA(I)/TA(I+II) and MPI-3 all suggest that the shales are within the oil window. Heavy components of free hydrocarbons (S-1) within the shales may have been recorded as part of the Rock-Eval S-2 peak resulting in the low T-max values. The oil and shale extracts analysed are similar according to their sterane and triterpane distributions, suggesting that the oil was generated by the shales. However burial depths of the Upper Miocene - Pliocene shale succession are not sufficient for thermal maturation to have occurred. It is inferred that intense volcanism during the Pliocene - Pleistocene may have played an important role in local maturation of the shale succession.