Both the mechanical and hydraulic behavior of black oil reservoirs is dominated simultaneously by the properties of the intact' rock and the discontinuities within such masses. When inter-connected, these discontinuities define individual blocks that may become unstable, when subjected to pressure and/or thermal gradients. Studies involving coupled stress, thermal and flow modeling, in reservoir engineering, using both mechanical and hydraulic properties for the rock fabric and incorporating the stress magnitude and its directionality, have demonstrated the concept that preferred directionality during waterflooding is stress related and progressive in time. 2-D and 3-D field applications illustrate that reservoirs are both reactive' and dynamic in nature and substantial changes to both the hydraulic and mechanical constitutive behavior are taking place during waterflooding operations.
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