AGB201501

Abstracts and References

Published: 15 June 2015

Thermal maturity assessment of middle triassic rocks and heat flow modeling in Agatovo-Suhindol area (central north Bulgaria)

Nikola Botoucharov, Megi Angelova

Abstract

The study area is in the Moesian Platform and more precisely in its southern most subsided part – South Moesian Platform Margin. The research object is Triassic section reached by boreholes in the Agatovo and Suhindol countryside area. The data base is mainly from 4 key wells - from west to east R-1 Agatovo, R-2 Suhindol, R-2 Agatovo and R-1 Suhindol. Geological and drilling information enables modeling of thermal evolution and heat flow in a broader age range. Therefore, allowing reconstruction of the geodynamic evolution in the study area. It is an important factor for the subsidence and transformation of organic matter in sedimentary rocks as well as generation of oil and gas.

The main objective of the research is to assess the thermal maturity of Middle Triassic rocks and modeling heat flow by the measured vitrinite reflectance (% Ro) in Mesozoic section. Thermal maturity of the Middle Triassic sediments varies between 1.09 and 1.79% Ro, which define them as mature to overmature deposits within the stages of hydrocarbon generation. This is a result of the great thickness of overburden rocks and burial depths of the Triassic sediments. Typical of the region is that the thermal maturity of the Triassic sediments increases from north to south, as in the same direction increases the thickness and depths not only of Lower-Middle Jurassic sequence, but of the entire Mesozoic complex.

The compiled 1-D geothermal model shows that during the deposition of the Middle Triassic sediments there were increased values of the heat flow. They are inherited from earlier extensional tectonics caused by the Late Permian and Early Triassic rifting. The study area model calculations demonstrate a heat flow of over 60 mW/m2 for the Anisian-Carnian age interval. Since the end of Carnian and in Norian-Rhaethian time the heat flow has been lower than in previous Triassic epochs and up to 50 mW/m2. This is a consequence of compressional tectonics during Cimmerian orogenesis in the Late Triassic leading to uplift and erosion of part of the section. Following the logic of the pattern we can summarize that the heat flow rises in stages of extension in the Triassic and Jurassic reaching values of up to 80-85 mW/m2 in Early-Middle Jurassic. And vice versa in periods of denudation heat flow decreases. Modeled heat flow decreases gradually thereafter, to remain around 50 mW/m2 from Late Jurassic until the Quaternary.

Keywords: Moesian Platform, Middle Triassic, thermal maturity, heat flow, modeling;

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Available Online First: 15 June 2015

References

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