Dimitrios RALLAKIS

Organic matter as a marker of fluid circulations and hydrothermal events: Consequences on the hydrogeochemical mechanisms acting in the foreland basin of the Northern Pyrenees

Raymond MICHELS – CREGU-GeoRessources

Major Results

Assessment of the TSR in the source rock kitchen of Deep Lacq. Using a series of equations from bibliography it was possible to perform mass balance calculations. Efficiency calculation of the petroleum system taking into account hydrocarbon generation, secondary cracking and destruction of hydrocarbons by TSR. Reconstruction of the evolution scenario of the petroleum/TSR kitchen.


A scenario was constructed for the petroleum kitchen taking into account the evolution of the source-rock (oil generation and secondary cracking in a closed system) and thermochemical sulfate reduction. The methodology is mainly based on the Deep Lacq petroleum system. However, Cassourat, Meillon-St (high H2S contents) and Rousse (no TSR) were also considered. The study revealed that the quantities of CH4 (consumed) and H2S (generated) are linked together by a liner equation, such as QCH4= 1.31QH2S (Figure). It was thus possible to have a first estimation of the total amount of hydrocarbons generated by the source rock by summing the volumes of the gas in place and the methane consumed by TSR.


Likewise, the amount of anhydrite consumed was also estimated. Attempts are being made to constrain the mass balance calculations by considering the total amount of CH4 generated in the petroleum kitchen by kerogen and the secondary cracking of oil (closed system). The final aim is to determine the overall efficiency of the petroleum system including total amount of hydrocarbons generated, trapped as well as the losses induced by TSR. The reconstructed scenario of fate of hydrocarbons shall be confronted to that of the reservoir filling (Bahnan, 2019) and the structural evolution of the basin as to contribute to a synthetic model.

TSR equation (Worden and Smalley, 1996; Mougin et al., 2007) and mass balance computations.