Investigating the Groningen gas reservoir: From passive seismic monitoring to experiments on effects of pore pressure on fault slip

Since the start of production in 1963, natural gas from the Groningen field has been an important source of energy and contributed significantly to the Dutch economy. However, since the 1990s, there have been increased incidences of induced earthquakes related to reservoir compaction caused by gas extraction and associated pore pressure reduction. In this EU-funded PhD project, I investigated if changes in the physical properties of the sandstone reservoir rock can be detected using seismic monitoring methods. In addition, I conducted laboratory experiments on sandstone to investigate the effects of pore pressure on the stability of simulated faults that cut the sandstone reservoir.

I used deep borehole recordings of seismic noise produced by human activity, such as passing trains, over two 5-month periods. Employing seismic wave interferometry, I was able to determine variations in wave speed in the reservoir with a very high accuracy around the single borehole studied. I found small increases in seismic wave speed that might be related to compaction of the reservoir during the two periods of data acquisition. Furthermore, I detected a temporary change in the level of the gas-water interface associated with drilling operations at 4.5 km distance from the borehole. I did not find any effects of earthquakes on wave speeds in the reservoir. However, my experiments suggest that the decrease in gas pressure that causes reservoir compaction also promotes unstable earthquake slip on faults, as opposed to quiet fault motion.