Abstract
We present a workflow linking coupled fluid-flow and geomechanical simulation with seismic modelling to predict seismic anisotropy induced by non-hydrostatic stress changes. We generate seismic models from coupled simulations to examine the relationship between reservoir geometry, stress path and seismic anisotropy. The results indicate that geometry influences the evolution of stress, which leads to stress-induced seismic anisotropy. Although stress anisotropy is high for the small reservoir, the effect of stress arching and the ability of the side-burden to support the excess load limit the overall change in effective stress and hence seismic anisotropy. For the extensive reservoir, stress anisotropy and induced seismic anisotropy are high. The extensive and elongate reservoirs experience significant compaction, where the inefficiency of the developed stress arching in the side-burden cannot support the excess load. The elongate reservoir displays significant stress asymmetry, with seismic anisotropy developing predominantly along the long-edge of the reservoir. We show that the link between stress path parameters and seismic anisotropy is complex, where the anisotropic symmetry is controlled not only by model geometry but also the nonlinear rock physics model used. Nevertheless, a workflow has been developed to model seismic anisotropy induced by non-hydrostatic stress changes, allowing field observations of anisotropy to be linked with geomechanical models.
Highlights
Extraction and injection of fluids within hydrocarbon reservoirs alters the in situ pore pressure leading to changes in the effective stress field within the reservoir and surrounding rocks
We present a workflow linking coupled fluid-flow and geomechanical simulation with seismic modelling to predict seismic anisotropy induced by non-hydrostatic stress changes
Stress anisotropy is high for the small reservoir, the effect of stress arching and the ability of the side-burden to support the excess load limit the overall change in effective stress and seismic anisotropy
Summary
Extraction and injection of fluids within hydrocarbon reservoirs alters the in situ pore pressure leading to changes in the effective stress field within the reservoir and surrounding rocks. A reduction in fluid pressure within a reservoir is often accompanied by a slower increase in the minimum effective horizontal stress with respect to the vertical effective stress change (e.g., Segura et al 2011) This asymmetry can result in the development of stress anisotropy that may promote elastic failure within the rock, such as fault reactivation and borehole deformation. Linking seismic anisotropy measurements with stress path requires a better understanding of the link between geomechanical deformation (evolution of stress and strain), fluid-flow, rock physical properties and seismic attributes. Poroelastoplasticity can incorporate matrix failure during simulation, allowing strain hardening and weakening to develop within the model This is especially important for modelling reservoir stress path and stress path asymmetry. Poroelastoplasticity enables the prediction of when and where failure occurs in the model, allowing us to model the likely microseismic response of a reservoir (Angus et al 2010, 2015)
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