Effects of poroelastic coupling on microseismic signatures

SUMMARY We develop an approach to model microseismicity triggered by fluid injection on the basis of the theory of poroelasticity accounting for the external stress field. Consideration of the fully coupled poroelastic field equations enables us to apply a Coulomb failure criterion using pore fluid pressure and stress tensor as well as the coefficient of friction. The poroelastic fields are calculated with the finite element method simulating fluid injection with constant injection rate into a 2D domain. The influence of diffusivity, injection rate and stress field on the occurrence of microseismicity is analyzed and compared to simulations based on pore fluid pressure diffusion only. We find that the spatio-temporal evolution of microearthquakes is little sensitive to changes in diffusivity but strongly sensitive to changes of injection rate. Moreover, we show that an external stress field with unequal principal stresses causes elongated microseismic clouds. These clouds are indistinguishable from those generated in poroelastic solids with anisotropic diffusivity for equal principal stresses. This shows that microseismicity distributions are dependent on the coupling of pore fluid pressure and stress field.