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<p>Shale hydration significantly influences shale matrix permeability during post-fracturing well shut-in, impacting long-term hydrocarbon production in deep shale reservoirs. Shale hydration is mainly triggered by interactions between clay minerals and water-based fracturing fluids. This process can cause permeability reduction through clay swelling, but can also generate microfractures that enhances fluid flow. In deep shale reservoirs, anisotropic in-situ stresses, coupled with high-temperature and high-pressure reservoir conditions, further complicate the hydration-induced permeability changes during post-fracturing well shut-in. Although many studies have examined shale hydration, most have focused on its effects under simplified stress conditions and short durations due to laboratory constraints. Therefore, this study conducted permeability experiments on deep shale cores from the Jiaoshiba block of the Sichuan Basin under a true triaxial stress state using the RTX-3000 Triaxial Rock Testing System, systematically analyzing the evolution characteristics of shale matrix permeability under hydration and the impacts of temperature and stress on this process. The experimental results reveal a three-stage matrix permeability evolution process during well shut-in: (i) the obstruction stage, in which the matrix permeability drops sharply due to pore blockage caused by clay swelling and particle migration; (ii) the saturation stage, in which hydration-induced microfractures form, partially offsetting permeability lost; and (iii) the recovery stage, in which the new microfracture-pore structure stabilizes, leading to a net matrix permeability increase. Further analysis shows that higher temperatures and longer hydration durations can promote the formation and interconnection of microfractures, enhancing shale matrix permeability recovery. Moreover, greater horizontal stress differences can help maintain the opening of microfractures, improving matrix permeability enhancement. The results of this study offer new insights into shale matrix permeability evolution during hydration in post-fracturing well shut-in in deep shale reservoirs, providing a theoretical basis for optimizing shut-in strategies.</p>

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Deep Shale Matrix Permeability Evolution During Well Shut-In Under True Triaxial Stress

  • 期刊论文

  • 发表日期：

    2025年8月20日

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  • Jinzhou Zhao,
  • Yanshan Guo,
  • Zhihao Yu,
  • Lan Ren,
  • Ran Lin,
  • Jianfa Wu,
  • Yi Song,
  • Cheng Shen

摘要

Shale hydration significantly influences shale matrix permeability during post-fracturing well shut-in, impacting long-term hydrocarbon production in deep shale reservoirs. Shale hydration is mainly triggered by interactions between clay minerals and water-based fracturing fluids. This process can cause permeability reduction through clay swelling, but can also generate microfractures that enhances fluid flow. In deep shale reservoirs, anisotropic in-situ stresses, coupled with high-temperature and high-pressure reservoir conditions, further complicate the hydration-induced permeability changes during post-fracturing well shut-in. Although many studies have examined shale hydration, most have focused on its effects under simplified stress conditions and short durations due to laboratory constraints. Therefore, this study conducted permeability experiments on deep shale cores from the Jiaoshiba block of the Sichuan Basin under a true triaxial stress state using the RTX-3000 Triaxial Rock Testing System, systematically analyzing the evolution characteristics of shale matrix permeability under hydration and the impacts of temperature and stress on this process. The experimental results reveal a three-stage matrix permeability evolution process during well shut-in: (i) the obstruction stage, in which the matrix permeability drops sharply due to pore blockage caused by clay swelling and particle migration; (ii) the saturation stage, in which hydration-induced microfractures form, partially offsetting permeability lost; and (iii) the recovery stage, in which the new microfracture-pore structure stabilizes, leading to a net matrix permeability increase. Further analysis shows that higher temperatures and longer hydration durations can promote the formation and interconnection of microfractures, enhancing shale matrix permeability recovery. Moreover, greater horizontal stress differences can help maintain the opening of microfractures, improving matrix permeability enhancement. The results of this study offer new insights into shale matrix permeability evolution during hydration in post-fracturing well shut-in in deep shale reservoirs, providing a theoretical basis for optimizing shut-in strategies.