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<p>This study has investigated the in situ stresses and pore pressure variations within deep fault zones of a shale gas reservoir in the Sichuan Basin, southwest China. An integrated field approach, including diagnostic fracture injection tests (DFIT), borehole imaging, and acoustic logging, was used to characterize stress magnitudes and orientations across a major fault zone. DFITs from wells at varying distances from the fault provided direct measurements of minimum horizontal stress and pore pressure. Borehole breakouts, drilling-induced fractures, and shear wave anisotropy constrained the maximum horizontal stress magnitudes and orientations. Results revealed a marked shear stress drop and ~ 25° rotation of maximum horizontal stress (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(S_{{{\text{Hmax}}}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>S</mi> <mtext>Hmax</mtext> </msub> </math></EquationSource> </InlineEquation>) orientations toward the fault strike within the damage zone. Pore pressure also decreases significantly in this zone, suggesting enhanced dissipation through a dense natural fracture network. Pore pressure decreases within the damage zone, leading to increased effective stresses and reduced slip tendency.These conditions—higher effective normal stress and lower shear stress—render fault slip unlikely under current reservoir pressures. The findings demonstrate that fault zone geomechanical properties, including high fracture density and compliant rock, strongly influence local stress states. Natural fractures act as conduits for pressure dissipation, while mechanical softening promotes stress rotation and relaxation. This field-based study strengthen the previous study results into stress and pore pressure behavior in faulted shale formations, improving upon prior work that relied primarily on numerical models or indirect log interpretations.</p>

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In Situ Three-Dimensional Stress Determination in an Overpressured Fault Zone Using Borehole Measurements

  • 期刊论文

  • 发表日期：

    2026年2月4日

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  • Ersi Xu,
  • Jingyu Huang,
  • Bin Xu,
  • Wenping Liu,
  • Biao Li

摘要

This study has investigated the in situ stresses and pore pressure variations within deep fault zones of a shale gas reservoir in the Sichuan Basin, southwest China. An integrated field approach, including diagnostic fracture injection tests (DFIT), borehole imaging, and acoustic logging, was used to characterize stress magnitudes and orientations across a major fault zone. DFITs from wells at varying distances from the fault provided direct measurements of minimum horizontal stress and pore pressure. Borehole breakouts, drilling-induced fractures, and shear wave anisotropy constrained the maximum horizontal stress magnitudes and orientations. Results revealed a marked shear stress drop and ~ 25° rotation of maximum horizontal stress ( \(S_{{{\text{Hmax}}}}\) S Hmax ) orientations toward the fault strike within the damage zone. Pore pressure also decreases significantly in this zone, suggesting enhanced dissipation through a dense natural fracture network. Pore pressure decreases within the damage zone, leading to increased effective stresses and reduced slip tendency.These conditions—higher effective normal stress and lower shear stress—render fault slip unlikely under current reservoir pressures. The findings demonstrate that fault zone geomechanical properties, including high fracture density and compliant rock, strongly influence local stress states. Natural fractures act as conduits for pressure dissipation, while mechanical softening promotes stress rotation and relaxation. This field-based study strengthen the previous study results into stress and pore pressure behavior in faulted shale formations, improving upon prior work that relied primarily on numerical models or indirect log interpretations.