Summary
The dynamic poroelastic model identifies how dynamic elastic properties
(P-wave and S-wave velocities and density) change during
reservoir production. This forms the basis of time-lapse seismic feasibility
studies. To provide accurate and meaningful predictions, the model requires
appropriate input from reservoir engineering (pore-pressure and saturation
variations) and geomechanics (stress and strain variations). In
stress-sensitive reservoirs, a geomechanical simulation, coupled with the
conventional reservoir simulation, updates vertical deformation and provides
the mean-effective-stress field in and around the reservoir. The key objective
of this work is to identify how combined reservoir and geomechanical effects
will influence predictions of the dynamic poroelastic model.
A method integrating reservoir engineering, geomechanics, and rock physics
is applied to a 3D synthetic case. The first task of this study is to model
deformation and stresses induced by exploitation within the reservoir and
surrounding formations. For this, the pore pressure extracted from the
reservoir simulation is introduced into the geomechanical model. Then, a
sensitivity analysis with different mechanical parameters (Young's modulus,
Poisson's ratio) and with different conditions (initial effective-stress ratio,
plasticity behavior) is performed on a 3D model that includes the reservoir and
its surroundings. The results of this geomechanical modeling are analyzed by
considering the compression effect, the stress arching effect, and the mean
effective-stress value in and above the reservoir. Then, the mean effective
stress resulting from each geomechanical simulation enables us to update
seismic velocities and the time shifts associated with seismic horizons, using
Hertz-Mindlin's model. Last, this approach, considering the geomechanical
aspect, is improved by the contribution of the fluid substitution on the
dynamic poroelastic model, taking the saturation effects into account. The
geomechanical approach is compared with some classical nongeomechanical
approaches commonly used. This work demonstrates that the geomechanical
approach influences the results in and around the reservoir. The time-shift
values of the seismic horizons produced using this approach would be detectable
on 4D-seismic data, and in this case study, the effect is much stronger than
the saturation effect alone.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
23 February 2006
- Meeting paper published:
13 June 2006
- Revised manuscript received:
1 December 2009
- Manuscript approved:
3 December 2009
- Published online:
1 April 2010
- Version of record:
20 April 2010
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