Quantification of natural microbial methane from generation to emission in the offshore Aquitaine: A basin modelling approach

Marine sediments near continental margins contain sedimentary organic matter (SOM) which is subject to the metabolic activity of micro-organisms during early diagenesis resulting in production biogenic methane. This process occurs at microscopic scale and anaerobic conditions. Here, we apply a new numerical approach simulate methane offshore Aquitaine (Bay Biscay) where gas seeps have been recently observed as result microbial activity. accounts for: (1) degradation labile-SOM fraction methane, (2) first order kinetics thermal thermo-labile-SOM into labile greater burial (3) decrease SOM reactivity with time. First, characterized through pyrolysis using Rock-Eval performed on cuttings collected from two wells located within seepage area. The system fed type III continental-derived immature (average Tmax < 425 °C). basin model built calibrated seismic well data. It for consumption required precipitate methane-derived authigenic carbonates are found widely distributed seafloor oxidation upward migration. A sensitivity analysis main input parameters quantify their impact expulsion/migration processes. Results led reference scenario Aquitaine. With this generated predominantly dissolved water transported by advective Migration mainly vertical source rock layers controlled sediment porosity strata geometry. Modelling can reproduce natural processes such migration emission points (gas seeps) previously mapped Basin. Our results suggest that sourced present-day active mean flow rate 27 Mg/y relatively lower than flux modelled Pleistocene reaching up 41 Mg/y. Calculated total lost along Shelf accordance estimated situ measurements acoustic signatures bubbling sites, ranges between 0.87 Tcf/My 1.48 Tcf/My. Here propose workflow assess predict occurrences environment recent matter. help better budget emitted naturally shelf area oceans may reach atmosphere negative climate environment.