Abstract: In steam-assisted gravity drainage (SAGD) wells containing superheavy oils, reservoir microfracturing will quickly establish a connection between the upper and lower horizontal wells, thus improving initiation efficiency. To understand the changes in permeability of microfractured reservoirs and to assess the efficacy of microfracturing processes, we measured the porosity and permeability parameters of oil sand reservoirs with different physical properties from the Fengcheng oilfield in Xinjiang, and studied how the pore volume, anisotropy, and temperature of the oil sands affected their permeability. The experimental results indicated that the variations in absolute permeability and effective water permeability of these sands with their porosity or volumetric strain are consistent with the Kozeny-Carman (or Kozeny-Poiseuille) equation, regardless of whether the sands were in their in situ or shear-dilated states. The absolute permeability of the sands in the horizontal direction was found to be greater than that in the vertical direction, whereas the opposite was observed for effective water permeability. Meanwhile, the injectant temperature in microfracturing processes appears to have a negligible impact on effective water permeability. On this basis, the differences in seepage during microfracturing and cyclic steam injection were investigated from a mechanistic perspective, with the use of finite-element analysis. It was shown in case calculations that microfracturing simulations should be performed using the effective water permeability.

Key words: microfracturing, terrestrial, oil sands, porosity, permeability, finite-element analysis