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Evaluation of Plio-Pleistocene formations in Katakolo (Greece) as sources of biogenic gas

Makri Vagia-Ioanna

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Summary

Katakolon oil and gas field is geographically located in Greece, more specifically in the North-Western Peloponnesus both onshore and offshore, while geologically it lies in the external-central Ionian zone. It is a small, yet relatively known field with proven reserves.Several exploration wells have been drilled in the wider area, facing oil and gas flowing from different layers. Mainly methane hydrocarbon shows appear in the onshore area which is mainly associated with biogenic gas while in the offshore area the gas shows are predominantly catagenetic associated with condensate.The main purpose of this study is the thermal maturity modelling of source rocks in both offshore and onshore locations, in terms of gas generation. Several 1D models are created to model these petroleum systems at individual well point locations throughout the field, utilizing PetroMod 2017.1, Schlumberger software. The examined petroleum systems refer to an onshore petroleum system with Plio-Pleistocene source rocks, prone to biogenic gas generation as well as to an offshore petroleum system with Triassic source rocks, prone to both oil and gas generation. Biogenic gas generation seems to be favoured regarding all the prevailing conditions in the onshore models. Rapid sedimentation, low geothermal gradient, shallow burial depth and the immaturity of the source rocks reinforce the modelling result of ongoing biomethane generation and expulsion. Still, in one of the onshore wells (MY-1) erosion events affect negatively the generation of biomethane. Different case scenarios in terms of source rock characteristics are examined for the offshore Katakolon models, since the evaporites have not been fully penetrated yet. Calibration has been performed for all the models, showing the chief importance of the overburden sediment amount and of the paleo-heat flow trend to the maturation of the underlying source rocks. A picture of maturity and generation potential at each point location is drawn indicating that source rock layers in the offshore West Katakolon field lie in the catagenesis stage. Generation of hydrocarbons has begun from around 200Ma, while gas expulsion in most case scenarios is not initiated prior to the trap formation. Even though gas expulsion is not possible from all the studied case scenarios, the gas entrapment is achieved from the ones that are, since the trap formation takes place between Langhian and early Zancleen (16-5Ma).

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