Synthetic seismic illumination of CO2 migration in fault zones

Abstract

Many subsurface geological storage sites for anthropogenic CO2 are situated in normal fault zones, where there is a risk of leakage as faults can act as fluid conduits. Optimal CO2 storage sites are generally located at depth which are most easily studied using seismic data, therefore monitoring and verification of the storage site is limited by seismic resolution. Seismic modelling of onshore analogues can be used to aid in understanding the seismic expression of geological features and the effect of CO2 migration. Synthetic seismic modelling of CO2 leakage in fault zones is performed in this study by studying the CO2 emitting siliciclastic Little Grand Wash fault (Utah, USA). The geomodel used to generate synthetic images is based on literature studies and comprises data both from the study area and comparable geological systems. The model is designed to represent leakage of a CO2 plume through a seal-bypass system in a fault zone. Scenarios of the system prior to CO2 exposure and prolonged mineralization of rocks is modelled, as well as reservoir conditions with added overburden to simulate a realistic storage scenario. Synthetic seismic images of each scenario were generated using a seismic modelling software based on input of the geomodel and associated elastic properties. The study of the generated synthetic seismic images confidently interprets several aspects of a CO2 plume migrating trough siliciclastic fault zones, implying that many features may be visible in conventional seismic data, and that fluid conduits in the fault zone may be resolvable using seismic p-cable technologies. If the goal is illuminating fluid-conduits prior to storage, there is room for an improved 3D model of the fault zone with more nuanced fault facies and variations in stratigraphic architecture. The findings of this study will ultimately aid in improving the interpretation of fluid migration in faults and expression and detectability of fault facies within a fault-zone.