-  3 well pair element of symmetry 2D model (UTF Phase B, Mukherjee, Gittins,  Edmunds and Kinsman)

 

                      

Geomechanical Issues - SAGD

• Increase in Temperature
       - Thermal expansion - heave
       - Horizontal stress increase
       - Transient vertical stress increase
• Increase in pressure
       - Volumetric expansion
       - Decrease effective stress
       - Shear dilation
       - Horizontal stress increase
       - Transient vertical stress increase

• Caprock Integrity with Combined Effects

Geomechanical Effects of SAGD

• Reservoir Behaviour
       - Nonlinear stress - strain response, hysteresis, stress path
       - Nonlinear compressibility
       - Shear dilation and permeability enhancement   
• Caprock Behaviour
       - Shear strength limitations
       - Undrained loading
       - Thermal stresses with heating
• Field Behaviour
       - Surface displacements
       - Stress evolution for future drilling

Reservoir Sand Effects

• Why operate SAGD at maximum "safe" pressures?
       - Higher T, lower viscosity
       - Shear dilation of the oil sand and permeability enhancement
• What are the benefits of shear dilation?
       - Permeability and porosity enhancement
       - Perm enhancement is directional
       - Thin vertical flow barriers can be broken enhancing vertical drainage
• Under what conditions will shear dilation occur?
       - Low effective stress
       - Shear failure

Shear Dilation of Sand at
Low Effective Confining
Stress

 

Summary

      - Geomechanical effects can be very important to a SAGD project
      - Understanding these effects is contingent on:
            - Correct interpretation of initial stress state
            - Correct understanding of stress - strain material
            - Correct modeling of that material behaviour in field scale model

References

      - Mukherjee, N.J., S.D., Edmunds, N.R. and Kisman, K.E., (1995) "A
 Comparison of Field Versus Forecast Performance for Phase B of the
UTF SAGD Project in the Athabasca Oil Sands", 6th UNITAR International
 Conference on Heavy Crude and Tar Sands, February 12-17, Houston,TX.