HR: 0830h
AN: S41E-0134    [PDF]
TI: Coupled Modeling of Time-Lapse Change in Seismic Propagation and Permeability in Fractured Reservoirs Due to Fluid Injection
AU: * Daley, T M
EM: tmdaley@lbl.gov
AF: Lawrence Berkeley National Lab, Earth Science Division, 1 Cyclotron Rd MS 90-1116, Berkeley, CA 94720
AU: Schoenberg, M A
EM: maschoenberg@lbl.gov
AF: Lawrence Berkeley National Lab, Earth Science Division, 1 Cyclotron Rd MS 90-1116, Berkeley, CA 94720
AU: Rutqvist, J
EM: jrutqvist@lbl.gov
AF: Lawrence Berkeley National Lab, Earth Science Division, 1 Cyclotron Rd MS 90-1116, Berkeley, CA 94720
AU: Nihei, K T
EM: ktnihei@lbl.gov
AF: Lawrence Berkeley National Lab, Earth Science Division, 1 Cyclotron Rd MS 90-1116, Berkeley, CA 94720
AB: For porous rock, the elasto-dynamic and fluid flow properties can be strongly dependent on effective static stress. Independent models (and computer codes) are typically used to study elasto-mechanical and hydro- mechanical changes in the subsurface due to changes in subsurface properties. We have coupled finite-difference elastic seismic and finite-element hydro-mechanical modelling codes and proposed constitutive relationships between effective stress and fracture properties (both mechanical stiffness and fracture permeability) thereby allowing us to model temporal and spatial variations in pore pressure, permeability and elastic (anisotropic) constants for fluid injection in a fractured reservoir. We assume that change in rock properties is due to pore pressure changing the effective stress which then affects the behavior of aligned micro-cracks and fractures much more than the behavior of the rock matrix background (which for this study is assumed essentially insensitive to changes in pore pressure). This implies that only the parts of the elastic compliance tensor and permeability tensor associated with the aligned fractures depend on changing stress. We then propose a constitutive relationship between fracture stiffness and effective stress and between fracture permeability and effective stress. These relationships are used to give the temporal and spatial changes (seismic and hydrologic) for a specific modeling problem. The 3D example presented is a vertically fractured layer within an otherwise homogeneous, impermeable medium. The fractures are assumed closely spaced (relative to a seismic wavelength) and parallel. Using the 2D hydro-mechanical code (Rocmass), we model the injection of fluid into the permeable, fractured layer. The spatial variation in pore pressure, permeability and elastic stiffness are calculated at different time steps. As the subsurface pore pressure changes due to injection, permeability changes and thus effects the spatial pore pressure distribution. Symmetry properties are used to map the results to 3D. The 3D variations in elastic stiffness (for a given time step) are used as input to a 3D, anisotropic, elastic, finite-difference seismic modeling code (Anisg3Dmpi) to calculate the seismic response. Different seismic acquisition geometries are investigated, including 3D surface seismic, VSP and horizontal well cross-well. For our initial fluid injection parameters, the VSP and cross-well geometries show measurable effects due to the fluid injection.
DE: 0902 Computational methods, seismic
DE: 3210 Modeling
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting