SAGD井微压裂储层渗透率变化规律研究

对超稠油SAGD井储层进行微压裂能够快速建立上下水平井连通，提高启动效率。为了掌握微压裂储层渗透率演变规律及评价微压裂效果，通过实验获取了新疆风城不同物性油砂储层的孔渗参数，研究了油砂的孔隙体积、各向异性及温度对渗透率的影响。实验结果表明，无论是原位还是剪切扩容后的状态，风城陆相油砂的绝对渗透率及水的有效渗透率随孔隙度或体应变的变化均遵从Kozeny Carman或Kozeny Poiseuille方程；同时，该油砂绝对渗透率为水平方向大于垂直方向，而水的有效渗透率则为垂直方向大于水平方向。同时，微压裂的注液温度对水的有效渗透率的影响可以忽略。在此基础上从机理出发探讨了微压裂和注蒸汽循环阶段的渗流差异，进一步运用有限元模拟手段，通过案例计算证实了微压裂模拟过程应采用水的有效渗透率。

Study on Patterns of Change in Oil Reserve Permeability During Microfracturing of SAGD Wells

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.