Correlation between hydrocarbon reservoir properties and induced seismicity in the Netherlands

Earthquakes induced by gas production are a social concern in the Netherlands. Over the last two decades, a total of about 350 such earthquakes have been recorded, with magnitudes ranging up to 3.5 on Richterʹs scale. The new Dutch mining law prescribes the operators to give a quantitative estimation of the likelihood of future seismic activity (hazard) and the associated damage (risk). This estimation has to be given for every onshore field (producing, or to be produced). A traditional probabilistic seismic hazard analysis (PSHA) can not give an estimation of the hazard for a field before the occurrence of seismic activity. We have therefore investigated the correlation between parameters related to reservoir and production properties and the occurrence of induced seismicity in a hydrocarbon field statistically, using Bayesʹ theorem and the Rule of Succession. Three key parameters have been identified that show a good correlation with the occurrence of earthquakes: pressure drop, fault density of the reservoir and stiffness ratio between seal- and reservoir rock. Based on the observed correlation a probability for the occurrence of earthquakes in fields that have no historical earthquake record has been calculated. This has resulted in the definition of four groups of hydrocarbon fields having all a different probability.