Seismogenic Index of Underground Fluid Injections and Productions

Abstract

AbstractThe seismogenic index quantifies a seismogenic reaction of rocks to a unit volume fluid impact. This quantity helps to forecast seismogenic effects of planned subsurface fluid operations. It facilitates a quantitative comparison of tectonic conditions and fluid operations in terms of their potential to induce earthquakes and to produce seismic hazard. The higher the seismogenic index, the higher the induced seismic hazard. Originally, the seismogenic index was proposed for seismicity induced by underground fluid injections. However, its broader applications are of interest. I derive the seismogenic index for fluid productions. In the case of production, the poroelastic coupling becomes principally important. I consider two limiting (end‐member) situations: a production or injection in a point of a poroelastic infinite continuum and a production or injection in a poroelastic layer embedded in an elastic half‐space. These two basic fluid source/sink configurations are prototypes of practical situations like a stimulation of an enhanced geothermal system and hydrocarbon production from a large‐area underground reservoir, respectively. I show that estimates of the seismogenic index from productions can be adopted for injections and vice versa. I provide estimates of the seismogenic index and of the poroelastic coupling characterizing the Groningen gas field. In an idealized homogeneous reservoir layer being similarly to the Groningen field at normal faulting, the presence of production‐induced seismicity indicates a combination of the friction coefficient and of the poroelastic coupling unfavorable for inducing seismicity by injections.