Numerical modelling of pore-pressure diffusion in a reservoir-induced seismicity site in northeast Brazil

Aderson F. do Nascimento, Rebecca J. Lunn, Patience A. Cowie

    Research output: Contribution to journalArticle

    Abstract

    A 3-D fluid-flow model is used to investigate pore-pressure diffusion as a mechanism for reservoir-induced seismicity (RIS) at the Açu reservoir in NE Brazil. The Açu dam is a 34-m high earth-filled dam constructed in 1983 on an area of Precambrian shield. Seismic activity in this area has been monitored over a 10-yr period (1987-1997 . The frequency of earthquakes clearly varies with seasonal fluctuations of the reservoir level. Information on the hydrological regime of the Açu reservoir (rainfall, vegetation, surface and subsurface storage, etc.) is used to set up a regional groundwater-flow model in order to obtain boundary conditions for a more detailed study of the area of seismic activity. To explain the observed time lag between maximum reservoir level and peak seismic activity we calculate the magnitude and timing of the maximum piezometric head in the depth range of observed seismic activity. By assuming that individual earthquake ruptures occur when the local piezometric head is at a maximum, values of bulk permeability, K, and storativity, S, are derived. If a 3-D homogenous subsurface permeability structure is assumed then the values of K and S obtained are not self-consistent and are physically unrealistic. However, if a high-permeability fault is embedded into, and explicitly coupled with, the surrounding lower-permeability matrix, then our estimates of subsurface hydraulic properties agree well with other field and laboratory measurements. The inclusion of a discrete fault plane in the model is consistent with the results of high-resolution seismic monitoring using a local digital network of stations, which show that the earthquake hypocentres define a set of steeply dipping NE-striking fault planes beneath the reservoir. © 2005 RAS.

    Original languageEnglish
    Pages (from-to)249-262
    Number of pages14
    JournalGeophysical Journal International
    Volume160
    Issue number1
    DOIs
    Publication statusPublished - Jan 2005

    Fingerprint

    reservoir-induced seismicity
    pore pressure
    permeability
    modeling
    fault plane
    earthquake hypocenter
    earthquake rupture
    earth dam
    hydrological regime
    hydraulic property
    groundwater flow
    fluid flow
    shield
    Precambrian
    boundary condition
    dam
    earthquake
    rainfall
    matrix
    seismic activity

    Keywords

    • Fault storativity
    • Modelling diffusion
    • Permeability
    • Reservoir-induced seismicity
    • Triggered seismicity

    Cite this

    do Nascimento, Aderson F. ; Lunn, Rebecca J. ; Cowie, Patience A. / Numerical modelling of pore-pressure diffusion in a reservoir-induced seismicity site in northeast Brazil. In: Geophysical Journal International. 2005 ; Vol. 160, No. 1. pp. 249-262.
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    abstract = "A 3-D fluid-flow model is used to investigate pore-pressure diffusion as a mechanism for reservoir-induced seismicity (RIS) at the A{\cc}u reservoir in NE Brazil. The A{\cc}u dam is a 34-m high earth-filled dam constructed in 1983 on an area of Precambrian shield. Seismic activity in this area has been monitored over a 10-yr period (1987-1997 . The frequency of earthquakes clearly varies with seasonal fluctuations of the reservoir level. Information on the hydrological regime of the A{\cc}u reservoir (rainfall, vegetation, surface and subsurface storage, etc.) is used to set up a regional groundwater-flow model in order to obtain boundary conditions for a more detailed study of the area of seismic activity. To explain the observed time lag between maximum reservoir level and peak seismic activity we calculate the magnitude and timing of the maximum piezometric head in the depth range of observed seismic activity. By assuming that individual earthquake ruptures occur when the local piezometric head is at a maximum, values of bulk permeability, K, and storativity, S, are derived. If a 3-D homogenous subsurface permeability structure is assumed then the values of K and S obtained are not self-consistent and are physically unrealistic. However, if a high-permeability fault is embedded into, and explicitly coupled with, the surrounding lower-permeability matrix, then our estimates of subsurface hydraulic properties agree well with other field and laboratory measurements. The inclusion of a discrete fault plane in the model is consistent with the results of high-resolution seismic monitoring using a local digital network of stations, which show that the earthquake hypocentres define a set of steeply dipping NE-striking fault planes beneath the reservoir. {\circledC} 2005 RAS.",
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    Numerical modelling of pore-pressure diffusion in a reservoir-induced seismicity site in northeast Brazil. / do Nascimento, Aderson F.; Lunn, Rebecca J.; Cowie, Patience A.

    In: Geophysical Journal International, Vol. 160, No. 1, 01.2005, p. 249-262.

    Research output: Contribution to journalArticle

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