(Calo et al, GJI, 2011)

Reservoir-Induced Seismicity

Victoria StevensFebruary 2012

References

• Talwani, P., 1997. On the nature of reservoir-induced seismicity, Pure and Applied Geophysics, 150, 473-492.

• Talwani, P., Chen, L. & Gahalaut, K., 2007. Seismogenic permeability, k(S), Journal of Geophysical Research-Solid Earth, 112.

• Gupta, H., 2002. A review of recent studies of triggered earthquakes by artificial water reservoirs with special emphasis on earthquakes in Koyna, Earth Science Reviews, 58, 279-310.

Plan of talk

• Introduction• Observations• Mechanisms• Diffusivity and permeability

Introduction

• Noticed first when Lake Mead (on Arizona-Nevada border) was filled

• We know how and when conditions change so can study response

• Triggered by as little as 20 m filling – crust already close to failure

• M 6.3 triggered by reservoir filling in Koyna, India – killed 200 people.

Worldwide distribution of reservoir induced seismicity, all over M 4

Seismicity at Monticello Reservoir

Lake Mead

Koyna

Seismicity from 1962 - present

India Earthquake Catalog 1960 to 1970 USGS NEIC PDE 2000 to 2012

Three time scales of seismicity

• Initial– Loading from water– increased pore pressure

• Delayed– Diffusion of pore pressure

• Protracted– Subsequent changes in water level

1. Initial seismicity• Effect of load

Initial seismicity

• Poroelastic constitutive equations:• – = volume strain increment– B = Skempton’s coefficient– = undrained Poisson’s ratio– G = shear modulus

• – = change in normal stress

2. Delayed seismicity

• Diffusion of pore pressure– – is permeability– is viscosity of pore fluid– is compressibility of bulk rock

Coupled poroelastic response

• Effect of load + diffusion of pore pressure– B Skempton’s coefficient– is the undrained Poisson’s ratio– H(t) is Heaviside unit step function– Assumptions……e.g. isotropic medium

Changes in elastic stress and pore pressure

3. Protracted seismicity

Diffusivity and permeability

• Talwani et al. 2007– Measured hydraulic diffusivity, C, from induced

earthquakes– Found all fractures that produced seismicity had

permeability of 5x10-16 to 5x10-14m-2

– Called this the seismogenic permeability– Assumed seismicity depends on rate of increase of

pore pressure, dp/dt.

Finding seismogenic values of C

Narrow range of k causes earthquakes

Hydraulic diffusivity

Permeability• • = viscosity of water, = porosity• and = compressibilities of water and rock

THE END