The Ambient Seismic Field at Groningen Gas Field: An Overview from the Surface to Reservoir Depth

Abstract

The long-term exploitation of the Groningen gas field led to compaction at reservoir depth, subsequent ground subsidence, and recently earthquakes. As part of an ongoing effort to quantify the hazard and risk in the region, several permanent and temporary seismic arrays have been deployed. As a result, the Groningen area is one of the seismologically best-instrumented areas worldwide. In this article, we describe several seismic experiments that were conducted in the region and take advantage of the numerous possibilities they offer to characterize the ambient seismic wavefield at the surface, in the shallow subsurface, and at reservoir depth. By means of beamforming, analysis of cross-correlation functions, surface-wave eigenfunction analysis, and correlations of neighboring frequencies, we are able to determine the main characteristics of the ambient seismic field (ASF), including the predominant propagation modes and phases. We retrieve clear multimode Rayleigh and Love waves, as well as and P waves, from cross correlations of the ASF. At reservoir depth, we show that the wavefield is largely trapped and reflected between geologic boundaries above and below the reservoir. This article reviews the characteristics of ASF observations with the goal of guiding future investigations of shallow structure of the Groningen area. Electronic Supplement: Figure showing cross-correlation envelope functions between the two deep borehole arrays.

Shear wave structure of a transect of the Los Angeles basin from multimode surface waves and H/V spectral ratio analysis

“…With dense arrays, both high-frequency surface waves (e.g. Lin et al 2013;Spica et al 2018b) and body waves (Nakata et al 2015;Spica et al 2018b) can be extracted and used to determine Figure 1. The LASSIE array and the Los Angeles basin area.…”

Shallow VS Imaging of the Groningen Area from Joint Inversion of Multimode Surface Waves and H/V Spectral Ratios

“…Part of this response includes the construction of a permanent shallow borehole microseismic network (the G-array; Fig. 1b) and the deployment of temporary nodal seismic experiments involving up to ∼415 three-component sensors (e.g., Spica et al, 2018).…”

“…1c), to characterize the subsurface with high resolution using a novel joint inversion of HVSR and Love-wave plus Rayleigh-wave dispersion, as measured from seismic interferometry with small-aperture array techniques. The ASF in the Groningen area is remarkably rich in higher-mode surface waves (Spica et al, 2018). Although higher modes are often considered as a problem and then avoided, they provide strong constraints on the velocity model because they are sensitive to different depths than the fundamental mode at the same frequency (e.g., Tomar et al, 2018).…”

“…Inversion results for these stations are highlighted in Figure 3. A detailed description of some of the seismic arrays in the Groningen area is provided in Spica et al (2018).…”

Ground-motion networks in the Groningen field: usability and consistency of surface recordings

“…Recordings from the flexible network have been used by NAM to infer the sub-surface shear-wave velocity profiles of different parts of the field down to 30, 100 and 800 m of depth, deployed with a mean inter-station spacing ranging up to 4 km. Studies making use of flexible network recordings include Spica et al (2018) and Stafford et al (2019).…”