Retrieval of the P- and S-velocity Structure of the Groningen Gas Reservoir Using Noise Interferometry

Abstract

The Groningen gas field in the Netherlands is the world's 7th largest onshore gas field and has been producing from 1963. Since 2013, the reservoir has been monitored by two geophone strings at reservoir level (3 km). For borehole SDM, 10 geophones with a natural frequency of 15-Hz are positioned from the top to bottom of the reservoir. We used seismic interferometry to determine, as accurately as possible, the inter-geophone P- and S-wave velocities from ambient noise. Cross-correlations were stacked for every 1 hour and 24(hours)*33(days) segments were obtained for each station pair. The cross-correlations show both diurnal and weekly variations reflecting fluctuations in cultural noise. The apparent P-wave travel time for each geophone pair is measured from the maximum of the vertical component cross-correlation for each of the hourly stacks. We used Kernel density estimations to obtain the maximum likelihood travel times of all the geophone pairs which were subsequently used to determine inter-geophone P-wave velocities. A good agreement was found between our estimated P velocity structure and well logging data. The S-velocity structure was obtained from the east-component cross-correlations. Because of the interference with P wave in east-component, the inferred S-velocity structure is less accurate.