Controlled laboratory experiments to assess the geomechanical influence of subsurface injection and depletion processes on 4D seismic responses

Abstract

ABSTRACTLaboratory experiments are performed with soft synthetic reservoir sandstone cemented under stress and with synthetic overburden (caprock) material consisting of compacted clay (kaolinite) in brine. The rock‐like materials are loaded mechanically under stress paths representative of stress changes occurring in the subsurface as a result of injection (increasing pore pressure) or depletion followed by injection into a storage reservoir. Static stress‐strain behaviour and multidirectional P‐ and S‐wave velocities are monitored during the tests. The tests with sandstone are performed on dry material and simple poroelastic modelling is performed to relate these data to the behaviour of fluid (water / CO2) saturated samples under the same stress paths. The focus is on identifying 4D seismic attributes that may be used in the field to interpret monitoring measurements. This could help diagnose stress changes in the overburden, signalling the risk of CO2 leakage from a reservoir if the compressive or tensile strength limit of the overburden is reached and of course to help quantify amounts of CO2 stored.