Induced seismicity of the Groningen gas field; history and recent developments

Induced seismicity of the Groningen gas field is caused by the production of gas. Because of the large areal extent of the reservoir, the long history of depletion, and the available data sets (which exist as a result of consequences and public unrest caused by induced seismicity), the field presents a valuable case for studying the relationships among geologic, flow-dynamic, geomechanical, and seismological models. Gas production from the Groningen field started in 1963. Induced seismicity of the field first was recorded in 1991 (M (sub L) 2.4). During the subsequent 10 years, induced seismicity stayed at a rate of about five events (M (sub L) > or = 1.5) per year. Starting in 2003, the number of events and magnitudes started to increase. In 2012, the largest event (M (sub L) 3.6) occurred, which caused the most damage to date. As a consequence, studies carried out in 2013 have fundamentally changed the way to look at the relationship between induced seismicity and gas depletion. There appears to be a close link between induced seismicity and reservoir compaction resulting from extraction of gas. Because compaction manifests itself as surface subsidence, accuracy of the subsidence measurements is deemed much more important than previously thought. The same holds true for quality and specific details of the static and dynamic models of the reservoir and its surroundings. In January 2014, it was decided to limit gas production in the central and highest-subsidence part of Groningen field and allow more production from the less compacted field periphery. Seismicity observed in 2014 was markedly different from that in earlier years. Although not yet statistically significant, this observation suggests a close link among production, compaction, and seismicity.