Alexy ELIAS BAHNAN

Fluid circulation and diagenesis of the Lacq Petroleum System: Impact of the geodynamic evolution

Supervisors:
Jacques Pironon and Cédric Carpentier
Université de Lorraine, CNRS, CREGU, GeoRessources lab
Eric Gaucher, Total, CSTJF, Pau

Major Results

The geodynamic evolution of the Pyrenees and its foreland basin controlled the diagenesis of the petroleum reservoirs in the Aquitaine basin. The Apto-Albian hyperextension triggered the circulation of petroleum and diagenetic fluids in the Deep Lacq reservoir, while the Paleogene inversion and compression drove deeply buried hydrothermal fluids to Upper Lacq

Abstract

The geodynamic evolution of basins exerts a major control on the evolution of the pathways, temperature, pressure and chemistry of circulating fluids. Recently, geodynamic models of the Pyrenees and the south Aquitaine basin were revisited and updated to include the involvement of an Early Cretaceous rifting phase that evolved to extreme crustal thinning coupled with mantle exhumation, followed by an inversion and convergence during the Late Cretaceous and the Paleogene. Using a multitude of petrographic, geochemical and modeling tools, we document how the Aptian hyperextension was coupled with TSR (Barré et al., 2018) and the circulation of Mg-rich fluids that partially dolomitized Deep Lacq (Elias Bahnan et al., in prep).

Mg was provided from the clay-rich formations at depths while salinities were the result of fluid interaction with the Triassic evaporites. Different fracturing episodes during the post-rift stage, when the N-S convergence started, connected Deep Lacq with a pool of fluids oversaturated with respect to calcites. A third fluid pulse, linked to the Eocene compression, precipitated massive anhydrites in Deep Lacq. At the same time in Upper Lacq, diagenesis was marked by orogeny-driven hydrothermal fluid circulations along the major faults and fractures on the crest of Lacq anticline (Barré et al., 2019; Elias Bahnan et al., 2020). Hydrothermal dolomites were documented with temperatures nearly 40°C higher than the surrounding host rocks (Elias Bahnan et al., 2019).

Summary figure showing a NNE-SSW regional cross-section of the Lacq Petroleum System and the main geodynamic- diagenetic events.

The diagenetic history of the giant Lacq gas field, witness to the apto-albian rifting and the Pyrenean orogeny, revealed by fluid and basin modeling.

Elias Bahnan, A., Pironon, J., Carpentier, C., Barré, G. and Gaucher, E.C. (2021) The diagenetic history of the giant Lacq gas field, witness to the apto-albian rifting and the Pyrenean orogeny, revealed by fluid and basin modeling. Marine and Petroleum Geology 133, 105250.

keywords: Lacq petroleum system, Aquitaine basin, Fluid inclusion modeling, Basin modeling, Sulfur-rich fluid system, TSR

DOI: https://doi.org/10.1016/j.marpetgeo.2021.105250

Impact of geodynamics on fluid circulation and diagenesis of carbonate reservoirs in a foreland basin: Example of the Upper Lacq reservoir (Aquitaine basin, SW France).

Elias Bahnan, A., Carpentier, C., Pironon, J., Ford, M., Ducoux, M., Barré, G., Mangenot, X., Gaucher, E.C. (2020). Impact of geodynamics on fluid circulation and diagenesis of carbonate reservoirs in a foreland basin: Example of the Upper Lacq reservoir (Aquitaine basin, SW France), Marine and Petroleum Geology (2019).

keywords:Carbonate diagenesis, Pyrenees, Aquitaine foreland basin, Upper Lacq reservoirs, Fluid inclusions, Basin modeling, Dolomitization, Hydrothermal fluids

DOI: https://doi.org/10.1016/j.marpetgeo.2019.08.047

Hydrothermal fluid circulations in the western Pyrenees: new data on stable isotopes, in-situ gas analysis and fluid inclusions.

Barré, G., Elias Bahnan, A., Motte, G., Ducoux, M., Hoareau, G., Laurent, D., Gaucher, E.C. (2019) Hydrothermal fluid circulations in the western Pyrenees: new data on stable isotopes, in-situ gas analysis and fluid inclusions. E3S Web. Conf. 98, 4.

keywords: Hydrothermal circulation, Western Pyrenees, H2S

DOI: https://doi:10.1051/e3sconf/20199801001

PhD Thesis: Fluid circulation and diagenesis of the Lacq Petroleum System : Impact of the geodynamic evolution

Elias Bahnan, A. (2019). Fluid circulation and diagenesis of the Lacq Petroleum System : Impact of the geodynamic evolution. Geosciences. Université de Lorraine.

keywords: Petrography, Geochemistry, Carbonate diagenesis, Fluid inclusions, Basin modeling

DOI: https://docnum.univ-lorraine.fr/public/DDOC_T_2019_0221_ELIAS_BAHNAN.pdf