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<p>The anelastic strain recovery (ASR) method provides an effective means of determining the three-dimensional in-situ stress tensor, playing a crucial supporting role in the efficient development of deep shale gas resources. In this study, the ASR method was applied to determine the full three-dimensional in-situ stress tensor of deep shale reservoirs in the Lower Silurian Longmaxi formation (3427–3446&#xa0;m depth) in the Yibin region, southern Sichuan Basin, China. In this study, we employed the ASR method to determine the in-situ stress tensor using three high-quality shale core samples from a 3.5-km deep borehole. To mitigate core fragmentation caused by clay mineral dehydration, samples were immediately submerged in a constant-temperature water bath with waterproof strain gauges. Meanwhile, to better constrain the in-situ stress magnitudes, we have integrated laboratory-scale shale permeability and compliance testing, providing robust constraints on the in-situ stress magnitudes in unconventional reservoirs. The test results show that the reservoir (3427−3446&#xa0;m) is a normal faulting stress environment (<i>S</i><sub>v</sub> &gt; <i>S</i><sub>H</sub> &gt; <i>S</i><sub>h</sub>). Based on image logging and paleomagnetic analysis, the orientation of the <i>S</i><sub>H</sub> is determined as ~ N72.3°&#xa0;E, which is consistent with the regional principal stress direction determined by the focal mechanism. This study provides key geomechanical parameters for the development of deep shale gas resources.</p>

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Investigating the In-Situ Stress State of the Longmaxi Shale Reservoir by Anelastic Strain Recovery Method in the Southern Sichuan Basin, China

  • 期刊论文

  • 发表日期：

    2025年10月28日

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  • Yifan Chen,
  • Zixuan Gao,
  • Chongyuan Zhang,
  • Qian Li,
  • Zijuan Hu,
  • Dongsheng Sun

摘要

The anelastic strain recovery (ASR) method provides an effective means of determining the three-dimensional in-situ stress tensor, playing a crucial supporting role in the efficient development of deep shale gas resources. In this study, the ASR method was applied to determine the full three-dimensional in-situ stress tensor of deep shale reservoirs in the Lower Silurian Longmaxi formation (3427–3446 m depth) in the Yibin region, southern Sichuan Basin, China. In this study, we employed the ASR method to determine the in-situ stress tensor using three high-quality shale core samples from a 3.5-km deep borehole. To mitigate core fragmentation caused by clay mineral dehydration, samples were immediately submerged in a constant-temperature water bath with waterproof strain gauges. Meanwhile, to better constrain the in-situ stress magnitudes, we have integrated laboratory-scale shale permeability and compliance testing, providing robust constraints on the in-situ stress magnitudes in unconventional reservoirs. The test results show that the reservoir (3427−3446 m) is a normal faulting stress environment (Sv > SH > Sh). Based on image logging and paleomagnetic analysis, the orientation of the SH is determined as ~ N72.3° E, which is consistent with the regional principal stress direction determined by the focal mechanism. This study provides key geomechanical parameters for the development of deep shale gas resources.