Seismic anisotropy as an indicator of reservoir quality in siliciclastic rocks

Kendall, J. M.; Fisher, Q.J.; Covey-Crump, S. J.; Maddock, J.; Carter, A.; Hall, Stephen A.; Wookey, James; Valcke, S.L.A.; Casey, Martin; Lloyd, Geoffrey E.; Ismaı̈l, Walid Ben

doi:10.1144/sp292.7

Cited by 41 publications

(46 citation statements)

References 44 publications

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“…where S 0 is the background (or intact) rock compliance estimated from either mineral composition [21] or high confining stress behaviour [22]. In this paper, we use the high stress approach because we have found using mineral composition does not yield consistent and reliable velocity predictions compare with observation.…”

Section: Discrete Microcrack Modelmentioning

confidence: 99%

Exploring Trends in Microcrack Properties of Sedimentary Rocks: An Audit of Dry and Water Saturated Sandstone Core Velocity–Stress Measurements

Angus

Fisher²,

Verdon³

2012

IJG

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Stress dependent rock physics models are being used more routinely to link mechanical deformation and stress perturbations to changes in seismic velocities and seismic anisotropy. In this paper, we invert for the effective non-linear microstructural parameters of 69 dry and saturated sandstone core samples. We evaluate the results in terms of the model input parameters of two non-linear rock physics models: A discrete and an analytic microstructural stress-dependent formulation. The results for the analytic model suggest that the global trend of the initial crack density is lower and initial aspect ratio is larger for the saturated samples compared to the corresponding dry samples. The initial aspect ratios for both the dry and saturated samples are tightly clustered between 0.0002 and 0.001, whereas the initial crack densities show more scatter. The results for the discrete model show higher crack densities for the saturated samples when compared to the corresponding dry samples. With increasing confining stress the crack densities decreases to almost identical values for both the dry and saturated samples. A key result of this paper is that there appears to be a stress dependence of the compliance ratio N T B B within many of the samples, possibly related to changing microcrack geometry with increasing confining stress. Furthermore, although the compliance ratio N T B B for dry samples shows a diffuse distribution between 0.4 and 2.0, for saturated samples the distribution is very tightly clustered around 0.5. As confining stresses increase the compliance ratio distributions for the dry and saturated samples become more diffuse but still noticeably different. This result is significant because it reaffirms previous observations that the compliance ratio can be used as an indicator of fluid content within cracks and fractures. From a practical perspective, an overarching purpose of this paper is to investigate the range of input parameters of the microstructural models under both dry and saturated conditions to improve prediction of stress dependent seismic velocity and anisotropy observed in time-lapse seismic data due to hydro-mechanical effects related to fluid production and injection.

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Section: Discrete Microcrack Modelmentioning

confidence: 99%

Exploring Trends in Microcrack Properties of Sedimentary Rocks: An Audit of Dry and Water Saturated Sandstone Core Velocity–Stress Measurements

Angus

Fisher²,

Verdon³

2012

IJG

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“…where S 0 ijkl is the background (or intact) rock compliance estimated from the mineral composition (Kendall et al, 2007) or behavior at high effective stresses (Sayers, 2002). The main assumptions in deriving these expressions are that the microcracks be rotationally invariant and thin.…”

Section: Rock Physics Modelmentioning

confidence: 99%

Exploring trends in microcrack properties of sedimentary rocks: An audit of dry-core velocity-stress measurements

et al. 2009

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Rock-physics models are used increasingly to link fluid and mechanical deformation parameters for dynamic elastic modeling. We explore the input parameters of an analytical stress-dependent rock-physics model. To do this, we invert for the stress-dependent microcrack parameters of more than 150 sedimentary rock velocity-stress core measurements taken from a literature survey. The inversion scheme is based on a microstructural effective-medium formulation defined by a second-rank crack-density tensor (scalar crack model) or by a second- and fourth-rank crack-density tensor (joint inversion model). Then the inversion results are used to explore and predict the stress-dependent elastic behavior of various sedimentary rock lithologies using an analytical microstructural rock-physics model via the initial modelinput parameters: initial crack aspect ratio and initial crack density. Estimates of initial crack aspect ratio are consistent among most lithologies with a mean of 0.0004, but for shales they differ up to several times in magnitude with a mean of 0.001. Estimates of initial aspect ratio are relatively insensitive to the inversion method, although the scalar crack inversion becomes less reliable at low values of normal-to-tangential crack compliance ratio [Formula: see text]. Initial crack density is sensitive to the degree of damage as well as the inversion procedure. An important implication is that the fourth-rank crack-density term is not necessarily negligible for most sedimentary rocks and evaluation of this term or [Formula: see text] is necessary for accurate prediction of initial crack density. This is especially important because recent studies suggest that [Formula: see text] can indicate fluid content in cracks.

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“…S 0 ijkl can be estimated from either the mineral composition (e.g., Kendall et al 2007) or the behaviour at high effective stresses, where it is assumed that the compliant pore space is completely closed (e.g., Sayers 2002). The additional compliance can be modelled using second-and fourth-rank crack density tensors a ij and b ijkl , respectively,…”

Section: Micro-structural Nonlinear Rock Physics Modelmentioning

confidence: 99%

Reservoir stress path and induced seismic anisotropy: results from linking coupled fluid-flow/geomechanical simulation with seismic modelling

et al. 2016

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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.

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Seismic anisotropy as an indicator of reservoir quality in siliciclastic rocks

Cited by 41 publications

References 44 publications

Exploring Trends in Microcrack Properties of Sedimentary Rocks: An Audit of Dry and Water Saturated Sandstone Core Velocity–Stress Measurements

Exploring Trends in Microcrack Properties of Sedimentary Rocks: An Audit of Dry and Water Saturated Sandstone Core Velocity–Stress Measurements

Exploring trends in microcrack properties of sedimentary rocks: An audit of dry-core velocity-stress measurements

Reservoir stress path and induced seismic anisotropy: results from linking coupled fluid-flow/geomechanical simulation with seismic modelling

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