Prediction of Top Surface Movements Due to SAGD (Steam Assisted Gravity Drainage) Based on Coupled Thermal Pressure Deformation Models

Xing Zhang* and Nick Koutsabeloulis
Schlumberger, UK
*[email protected]

Steam assisted gravity drainage (SAGD) is a new oil production technology for the recovery of heavy oil and bitumen. In these fields, the top surface movements that are caused by thermal expansion of reservoir rocks due to injected steam, is a major concern in many environment issues. This is particularly true for those faulted reservoirs that are close to the top surface. A coupled thermal-pressure-deformation model has been used to predict the movements of overburden on a cross-section of a studied field, the associated changes in stress and strain and the potential for fault reactivation during a production period of 33 years. This field has a reservoir thickness of about 250 m, overburden thickness of about 350 m, temperature change of up to 190° C and pressure depletion of up to 190 psi. The intact rock was simulated as an elasto-plastic material and the faults were simulated as Mohr-Coulomb materials. Four scenarios were examined to account for the uncertainty in mechanical properties of overburden and reservoir rock, such as Young’s modulus, Poisson’s ratio and thermal expansion coefficient. After 33 years of production, about 0.155 m of upward movement at the top surface above the reservoir was predicted under the given conditions. Also there is a high risk for fault reactivation due to the expansion of the reservoir rock. The predicted upward movement of the overburden decreases with decreasing Young’s modulus and thermal expansion coefficient, and increases with increasing Poisson’s ratio due to the increase in bulk modulus.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain