Fault reactivation mechanisms and dynamic rupture modelling of depletion-induced seismic events in a Rotliegend gas reservoir

Abstract

Understanding the mechanisms and key parameters controlling depletion-induced seismicity is key for seismic hazard analyses and the design of mitigation measures. In this paper a methodology is presented to model in 2D the static stress development on faults offsetting depleting reservoir compartments, reactivation of the fault, nucleation of seismic instability, and the subsequent fully dynamic rupture including seismic fault rupture and near-field wave propagation. Slip-dependent reduction of the fault's strength (cohesion and friction) was used to model the development of the instability and seismic rupture. The inclusion of the dynamic calculation allows for a closer comparison to field observables such as borehole seismic data compared to traditional static geomechanical models. We applied this model procedure to a fault and stratigraphy typical for the Groningen field, and compared the results for an offset fault to a fault without offset. A non-zero offset on the fault strongly influenced the stress distribution along the fault due to stress concentrations in the near-fault area close to the top of the hanging wall and the base of the footwall. The heterogeneous stress distribution not only controlled where nucleation occurred within the reservoir interval, but also influenced the subsequent propagation of seismic rupture with low stresses inhibiting the propagation of slip. In a reservoir without offset the stress distribution was relatively uniform throughout the reservoir depth interval. Reactivation occurred at a much larger pressure decrease, but the subsequent seismic event was much larger due to the more uniform state of stress within the reservoir. In both cases the models predicted a unidirectional downward-propagating rupture, with the largest wave amplitudes being radiated downwards into the hanging wall. This study showed how a realistic seismic event could be successfully modelled, including the depletion-induced stressing, nucleation, dynamic propagation, and wave propagation. The influence of fault offset on the depletion-induced stress is significant; the heterogeneous stress development along offset faults not only strongly controls the timing and location of a seismic slip, but also influences the subsequent rupture size of the dynamic event.

Geomechanical models for induced seismicity in the Netherlands: inferences from simplified analytical, finite element and rupture model approaches

“…Buijze et al, 2017) show that the ratio of seismic and aseismic slip is likely to increase as a function of rupture length.…”

Fully Dynamic Spontaneous Rupture Due to Quasi‐Static Pore Pressure and Poroelastic Effects: An Implicit Nonlinear Computational Model of Fluid‐Induced Seismic Events

“…Cappa and Rutqvist (2012) provided a more relevant study where they first solved a coupled quasi-static poroelastic equation iteratively using two existing codes and then directly used the stress state at the onset of failure as an input for the dynamic wave modeling. Similar work is presented by Buijze et al (2017). Lastly, we also mention a code that offers both poroelastic and elasto-dynamic modules, suitable for solving a coupled injection problem and a dynamic rupture problem, respectively (Ali, 2014;Meng, 2017).…”

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

“…However, the evolution of the yield envelope with strain and the effects of loading rate on stress-strain and yield behavior are of key importance in determining the reservoir response to the partitioning between elastic and inelastic strain. 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).…”