From checking deterministic predictions to probabilities, scenarios and control loops for regulatory supervision

Abstract

Prediction of gas-production-induced subsidence and seismicity is much more difficult and uncertain than generally recognised in the past. It is now widely accepted that uncertainties in predicted subsidence and seismicity are large prior to and during the initial stages of production. At later stages, predictions remain highly uncertain for periods more than three to five years into the future. This requires a different regulatory framework to ensure that associated risks remain within accepted boundaries. Previously, single-scenario operator predictions were checked against field measurements.When subsidence or seismicity started to deviate beyond claimed uncertainties, the operator was asked to provide prediction updates. The practice was long considered acceptable, as structural damage to buildings and infrastructure or personal risk to people was not expected. This all changed following the 2012 Huizinge seismic event, necessitating better identification, assessment and ranking of risks, the use of scenarios, probabilistic forecasting and a much intensified field monitoring and control loop. It requires that the regulator becomes actively involved in assuring the integrated control loop of risk identification, predictions, monitoring, updating, mitigation measures and the closing of knowledge gaps, to ensure that subsidence (rate) and induced seismicity remain within acceptable limits. And it requires that this increased involvement of the regulator is supported in the mining law and by appropriate conditions in the Production Plan assent.

Earthquake hazard and risk analysis for natural and induced seismicity: towards objective assessments in the face of uncertainty

“…The history of Mmax estimates for the Groningen field is worth briefly summarising. The earliest estimate was made by a body called Begeleidingscommissie Onderzoek Aardbevingen (BOA, Advisory Committee on Earthquake Investigation), which in 1993 issued a report that estimated Mmax as being in the range 2.9 to 3.3 (de Waal et al, 2017), although it should be noted that this was not specifically for the Groningen field but rather for earthquakes around Assen, south of the Groningen field. KNMI subsequently issued new estimates in 1995, for which two approaches were used: the first was based on the cumulative trend of released seismic energy, which yielded an Mmax of 3.3; the second was based on the dimensions of geological faults, which gave an Mmax of 3.5.…”

Deformation Behavior of Sandstones From the Seismogenic Groningen Gas Field: Role of Inelastic Versus Elastic Mechanisms

“…This partitioning directly controls the evolution of compaction and hence surface subsidence during production (Mallman & Zoback, 2007;Schutjens et al, 1995), and the stresses (Buijze et al, 2017) and elastic energy available to drive induced seismicity and associated energy dissipating processes occurring upon fault rupture (Cooke & Madden, 2014;Mcgarr, 1999;Shipton et al, 2013). In recent years, the onset of significant induced seismicity in strongly depleted reservoirs, such as the large Groningen field in the NE Netherlands (Grotsch et al, 2011), has created an urgent need to understand these effects much better (e.g., de Waal et al, 2017;Spiers et al, 2017). This paper addresses this need.…”

The Groningen Case: When Science Becomes Part of the Problem, Not the Solution

“…Earthquakes with magnitudes of M 1.8 and higher are reported to be felt by people, whereas earthquakes with magnitudes of M 2.0 and higher have caused nonstructural damage to buildings (e.g., cracks) (de Waal et al, 2017). In the beginning of the 1990s, the maximum expected magnitude was estimated around M 3.0, however this value was systematically raised to about M 4.0 prior to the 2012 Huizinge earthquake and M 5.0 after the Huizinge earthquake (de Waal et al, 2017).…”