Diagenetic evolution of fault zones in Urgonian microporous carbonates, impact on reservoir properties (Provence – SE France)

Abstract

<jats:p>Abstract. Microporous carbonate rocks form important reservoirs with high a permeability variability depending of sedimentary, structural and diagenetic factors. Carbonates are very sensitive to fluids-rock interactions that trigger to secondary processes like cementation and dissolution leading to reservoir properties modifications. As they can act as drains or barriers, fault zones influence the fluid flows in the upper part of Earth crust and increase the fluid-rock interactions. The aim of this study is to identify fault zone impact on fluid flows and reservoir properties during basin geodynamic history. The study focuses on 2 fault zones of the Eastern part of La Fare Anticlinal (SE France) where Urgonian microporous carbonates underwent polyphase tectonics and diagenesis. We took 122 samples along 4 transects cross-cutting two fault zones. Porosity values have been measured on 92 dry plugs. Diagenetic properties of samples have been determined on 92 thin sections using Polarized Light Microscopy, cathodoluminescence, red alizarin, SEM and isotopic measurements (δ13C and δ18O). Height calcite cement stages and 2 micrite micro-fabrics have been identified. This study highlight that fault zones acted as drain canalizing low temperature fluids at their onset, and induced fault zone cementation with two cementation phases, what has strongly altered and modified local reservoir properties. </jats:p>