Steam injection by Cyclic Steam Stimulation (CSS) and Steamflood (SF) are the selected enhanced oil recovery methods in a Kuwait shallow formation. Initial single wells and recent 5-spot pilots for CSS has production affected by sanding issues from the unconsolidated formation. A robust reservoir geomechanical model and cap rock integrity characterization on a field scale is a prerequisite for successful design and implementation of the two target steam-based EOR techniques for commercial exploitation.
Conventional geomechanical modeling approaches normally depend on history matching of the in-situ rock failure. However, lack of quality data measurements for minimum and maximum horizontal stress was major challenge for soft sediment rock.
Unconsolidated formation have their own inherent issues. Rock being weak and soft, it has low strength, as exhibited by the unconfined compressive strength (UCS). It also has comparatively lower values for the elastic moduli. Most of the time, the Leak Off Tests (LOT) carried out in such formation lead to inconclusive and questionable interpretation, as the pressure regime used is extremely low and this leads to uncertainty in stress measurement. Any thermal EOR project in such shallow-depth and unconsolidated formation heavily relies on a competent cap rock in place, whose integrity under the combined effect of thermo-mechanical-stress can be put to severe test.
To overcome the challenges of: a) weak soft sediments having low rock strength and elastic moduli, b) uncertainty in the stress measurement, c) inconclusive interpretation of leak off tests (LOT), a novel method was suggested. An Integrated Stress Analysis (ISA) approach was used for geomechanical modeling to evaluate magnitude of horizontal stresses from advanced sonic measurements and 3D dipole radial profiles. Data can be further used for estimating rock mechanical properties, stress orientation and Transverse Isotropy of Vertical symmetry axis (TIV) parameters.
A comprehensive anisotropic geomechanical model was built from the ISA and advanced 3D sonic output, which was validated using results from independently acquired minifracs run in offset wells.
This model could accurately predict potential drilling hazards and wellbore breakout. More than 10% acoustic anisotropy in horizontal stress was also found in sand intervals, which requires more careful approach while deciding the injection parameters. Multi-well analysis and geomechanical modeling also indicated variation in horizontal stresses ratio and direction across the field.
This paper provides a new approach for stress estimation of shallow heavy oil formation demonstrating how rock can behave as anisotropic material from sonic measurements, resulting in better constrain of tectonic and effective stresses. As special tool required to conduct minifrac in each wells and it is costly, using this novel approach to estimate stress magnitude is preferred.