Over the past decade, a steep increase in the number of seismic events has been observed in the Groningen gas field, the Netherlands. It is generally accepted that these are induced by compaction of the reservoir rock due to extensive depletion, causing a buildup of strain energy in faults that may be released seismically. We address the possible triggering of fault slip by the transient pressure field surrounding a well that has undergone a sudden rate change. Assuming a unilateral decoupling between displacement and pressure, numerical experiments are conducted using a sequential finite volume-finite element solution strategy that fully incorporates second-order terms in the radial flow equation. We investigate an idealized Groningen-like geometry to discover whether the hypothesized possibility of triggering-induced seismicity exists, explore how some controllable and uncontrollable variables influence its severity, and possibly provide clues on how production strategy might be able to avoid its occurrence. The results demonstrate that sudden production changes can indeed trigger near-well seismic events, but that the effect is very small compared to other potential causes. Changing from sudden to gradual changes in well rates is therefore not expected to lead to a significant reduction in the number or magnitude of production-induced earthquakes in the Groningen field.
- Natural gas
- Production-induced seismicity