Contribution of paleopiezometric analysis of calcite twins and stylolites roughness to understanding the tectonic and burial history of the sedimentary basins of the West African margin (South Atlantic)

• Main Author: Bah, Boubacar
• Other Authors: Institut des Sciences de la Terre de Paris (iSTeP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Université, Olivier Lacombe, Nicolas Beaudoin
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Calcite twins; Paleopiezometry; Burial history; South Atlantic ocean; Passive margins; Stylolites; Macles de la calcite; Paléopiézométrie; Histoire d'enfouissement; Atlantique sud; Marges passives; [SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology; [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics; [SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography; [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; South Atlantic Ocean
• Online Access: https://theses.hal.science/tel-04125238; https://theses.hal.science/tel-04125238/document; https://theses.hal.science/tel-04125238/file/BAH_Boubacar_these_2023.pdf

This thesis aims to test methodologies allowing the reconstruction of the evolution of reservoir properties and their pressure. This manuscript presents (1) a petrological characterization of the reservoir rocks with an estimation of the timing of porosity evolution, (2) the results of a paleopiezometric study, and (3) an evolution of effective stresses and potential fluid (over)pressures that prevailed in the carbonate reservoir during its evolution. These tools allow the reconstruction of the burial history and the paleostresses experienced by carbonate reservoirs in a passive margin. For this purpose, this work was based on a coupled approach of two complementary paleopiezometric tools combining the inversion of calcite twin data and stylolite roughness data. This approach was combined with petrographic, geochemical, geomechanical and geochronological analyses to fully characterize the reservoir. The studied material during this thesis consists of offshore cores recovered from deep wells provided by TotalEnergies located in the Lower Congo and Kwanza basins on the West African margin of the South Atlantic Ocean. These basins underwent a rifting event in the early Cretaceous times (145.5 - 112 Ma). The study of the porosity destruction of the pre-salt reservoirs of the syn-rift TOCA formation of Barremian age (130-125 Ma) from offshore core located in the Lower Congo basin revealed that the initial porosity was reduced to its current value of 4-8% during the first 35 Ma of its burial history, reaching ~10% after only 10 Ma, i.e. in the first 400-500 meters of burial and that the current porosity has not evolved significantly since 95 Ma (end of stylolitization). This study has shown that the outcome of reservoir properties in bioclastic carbonate formations such as the TOCA formation may be largely controlled by early and very shallow diagenetic processes rather than by mesogenetic reactions that occur later in the burial history. A paleopiezometric study was carried out in order to reconstruct the burial and ...