Characterization of Reservoir Heterogeneity from Surface Deformation

Abstract:

In our earlier work we resolved complex evolution of pressure fronts in a heavy
oil reservoir undergoing cyclic steam stimulation. Our method was based on
solving a regularized inverse problem for inverting the pore pressure change
from surface displacements. In this work we extend our method to recover
sharp contrasts in induced reservoir pressure that may be due to permeability
barriers or hydraulically conductive faults. We demonstrate our method by
inverting the pressure change from uplift observations for a synthetic model
of a heterogeneous reservoir undergoing fluid injection. Using the theory of
constrained optimization, we invert values and locations of sharp pressure
contrasts from noisy measurements of surface deformation, and estimate the
location of an impermeable boundary between reservoir compartments.

In our synthetic model, two highly permeable reservoir compartments
separated by a nearly impermeable barrier (first panel) undergo fluid injec-
tion. We simulate pressure evolution within the reservoir (second panel) and
model surface deformation induced by the subsurface pressure change (third
panel), adding measurement noise to the result. We invert the noisy sur-
face uplift measurements by solving a constrained optimization problem with
Tikhonov regularization (fourth panel). The result achieves a good inversion
quality in areas of finite pressure change but provides only a rough estimate
for the barrier location. However, applying our new inversion technique with a
total-variation regularization that favors sharp model contrasts while penalizing
oscillations, we achieve a more accurate approximation of the permeability
barrier as a level set of the inverted pressure field (fifth panel).

Our new method provides a potentially useful tool for locating sharp
subsurface pressure contrasts from surface uplift observations. The method
can be used in a variety of applications for identifying subsurface permeabil-
ity heterogeneities (such as seals and hydraulically conductive faults) from
InSAR, tilt or GPS measurements of the induced surface deformation.