Tectonic‐Related Fracture Infillings in Carbonate Reservoirs: Insights From the Campanian–Maastrichtian System of Jebel Cherahil, Central Tunisia

ABSTRACT The present work aims to highlight the relationship between the fractures infillings and the polyphased tectonics that affected the Campanian–Maastrichtian Abiod Formation in Jebel Cherahil (Central Tunisia). This formation consists of a 100–150 m thick carbonate succession known in Tunisia as an oil producing fractured reservoir. The study area corresponds to a zone of deformation showing several families of normal and reverse faults associated with dense fracture networks. Aiming to reconstruct the different tectonic phases having affected this carbonate reservoir, a macrotectonic field observation completed by examination of aerial photos and a microtectonic analysis of the different deformation elements was conducted. The microtectonic indices (direction, dip, dip direction, pitch) are measured over a large extent of outcrops of the Abiod Formation and then represented as a stereographic projection using GeoOrient software. The macrotectonic and microtectonic studies were followed by petrographic and micro‐stratigraphic analyses of the associated fractures infillings. Twenty samples were taken from different fractures and then examined with a polarising microscope and cathodoluminescence. The tectonic analysis, taking into account the previous works in the region, allows identifying three tectonic phases that have marked the Abiod Formation reservoir in Central Tunisia including the study area. A distensive phase during the Cretaceous–Tertiary transition, followed by two compressive phases respectively during Late Miocene and post‐Villafranchian. These tectonic events were largely recognised by several previous tectonic studies in Central Tunisia. The quality and the freshness of the outcrops allow distinguishing three main types of infillings: (i) dark to dark red karstic calcite and dolomite (ii) altered calcite and dolomite (iii) brecciated calcite. According to the microstratigraphic analysis, the latter represent three successive generations of infillings. Considering the different analytical results, it is thought that the infillings are respectively related to the already identified three tectonic phases. The present work provides a new and reliable proxy that highlights the relationship between tectonics and fractures infillings, which enhances the microtectonic analysis results. Such an approach strengthens in addition the knowledge on the fractured carbonate reservoir as it allows reconstructing the contemporaneous tectonic phases and then the timing of hydrocarbon migration.