Geomechanical modelling of subsidence and induced seismicity in a gas reservoir

Abstract

Reservoir compaction and associated surface subsidence, fault reactivation and induced earthquakes are observed in many petroleum fields worldwide. A better understanding of the geomechanical behaviour of reservoir rocks and neighbouring rock bodies is therefore becoming increasingly important within the petroleum industry. Several monitoring techniques for these phenomena exist, but methods of modelling reservoir geomechanical behaviour are hindered by clear limitations. This study discusses different suspected mechanisms of induced seismicity related to oil and gas production and their significance in varying reservoir environments. In support of this discussion, relevant background theory is presented together with a case study of induced seismicity in the Groningen Gas Field in the northern Netherlands. The aim of this thesis is to use a Modified Discrete Element Method proposed by (H. T. Alassi, 2008) to model the geomechanical behaviour in a depleting gas reservoir. Multiple scenarios have been modelled to investigate the significance of the suspected underlying mechanisms of seismicity and subsidence observed in the Groningen Field. It was found that depletion of a reservoir has the potential to induce rock failure on faults inside and in contact with the depleted zone as well as causing significant surface subsidence. It is also emphasized that improvements of the method and further research is needed to fully understand the significance of the underlying mechanisms.