GPR characterization of a naturally fractured siliciclastic reservoir on Svalbard, Arctic Norway

A naturally fractured siliciclastic aquifer on Svalbard is being evaluated as a potential CO₂ sequestration site for a local power plant. Well tests indicate substantial underpressure in the 700-1000 m deep reservoir, without a well-constrained cause. However, since the reservoir is gently dipping, and thus exposed at the surface 15 km up-dip from the planned injection site, this configuration requires pressure barriers to compartmentalize the reservoir. Outcrop mapping indicates the presence of m-scale offset faults (i.e. below the resolution of the existing seismic data) and igneous intrusions, both of which may act as impermeable structural discontinuities. Igneous intrusions are also imaged using regional geophysical data sets (2D seismic, magnetic). However, their orientation and dimension are poorly constrained by the present data set. In order to map and quantify these features, a 10 km² irregular grid of GPR profiles (100 km total length) on surface outcrops of the target formation was carried out in April 2013 to determine the feasibility of using GPR data to characterize the reservoir. Our study indicates that large amounts of geologically meaningful GPR data can be acquired cost- and time-effectively directly on the top of the targeted reservoir.