Geomechanical and Thermal Reservoir Simulation Demonstrates SAGD Enhancement Due to Shear Dilation

摘要

A novel numerical analysis is described, in which the steamassistedrngravity drainage (SAGD) recovery process inrnbituminous oil sand is studied. A geomechanical/reservoirrnsimulator was modified to incorporate the absoluternpermeability increases resulting from the progressive shearrndilation of oil sands. The objective was to obtain a realisticrnprediction of shear dilation, as the oil sands approached failurernand beyond, and the concomitant increases in permeability.rnChanges in the in situ stresses that caused this dilation wererndue to the combined effects of reduced effective stress withrnhigh-pressure steam injection, and increased deviatoric stressrnwith thermal expansion under lateral confinement. Thernresultant volumetric strains were used to modify the absoluternpermeability characteristics of the oil sands as the SAGDrnprocess progressed. The spatial and temporal growth ofrnenhanced permeability zones resulted in an accelerated steamrnchamber growth.rnThe relationship between volumetric strains and absoluternpermeability changes was obtained from existing laboratoryrndata on quality specimens of non-bituminous Athabasca oilrnsands. The source sample was obtained from an outcroppingrnof the McMurray Formation, thus avoiding most of the samplerndisturbance associated with unconsolidated core obtainedrnconventionally. Under triaxial loading, the resultantrnvolumetric strains increased absolute permeabilities by arnfactor of 4 to 6.rnThe analysis is innovative in that the model used anrneffective stress approach, and used the volumetric strains tornmodify absolute permeabilities. Thus, the encroaching SAGDrnsteam chamber was found to modify the stress regime, whichrnin turn modified the permeabilities within the reservoir.rnGeomechanical enhancement of the SAGD process was foundrnto be a significant beneficial effect, and would be increased byrnoperating the SAGD process at higher injection pressures.