<p>The reservoir rocks exist within geological environments characterized by elevated true-triaxial stress, pore pressure, and temperature. Understanding the coupled effects of temperature and true-triaxial stress on three-directional permeability is crucial for the efficient extraction of underground resources. Therefore, this study employs a self-developed true-triaxial geophysical imaging cell equipped with a temperature-controlled module to conduct three-directional helium permeability tests on purple sandstone. A stepwise loading path is adopted in this study to examine the influence of temperature (from 20 to 80 °C) and true-triaxial stress on three-dimensional permeability. As a result of inherent structural heterogeneity, the three-directional permeability exhibits significant anisotropy even under isotropic stress conditions. Under the coupled effects of thermal expansion and stress compaction, the three-directional permeability decreases with increasing temperature and principal stresses, and its sensitivity exhibits a negative correlation with both temperature and stress levels. This study introduces anisotropy ratios to quantitatively characterize the anisotropy degree in three-directional permeability (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${{k_{y} } \mathord{\left/ {\vphantom {{k_{y} } {k_{x} }}} \right. \kern-0pt} {k_{x} }}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>k</mi> <mi>y</mi> </msub> <mrow> <mfenced open="/"> <mphantom> <mpadded width="0pt"> <msub> <mi>k</mi> <mi>y</mi> </msub> <msub> <mi>k</mi> <mi>x</mi> </msub> </mpadded> </mphantom> </mfenced> </mrow> <msub> <mi>k</mi> <mi>x</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq2"> <EquationSource Format="TEX">${{k_{z} } \mathord{\left/ {\vphantom {{k_{z} } {k_{x} }}} \right. \kern-0pt} {k_{x} }}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>k</mi> <mi>z</mi> </msub> <mrow> <mfenced open="/"> <mphantom> <mpadded width="0pt"> <msub> <mi>k</mi> <mi>z</mi> </msub> <msub> <mi>k</mi> <mi>x</mi> </msub> </mpadded> </mphantom> </mfenced> </mrow> <msub> <mi>k</mi> <mi>x</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq3"> <EquationSource Format="TEX">${{k_{z} } \mathord{\left/ {\vphantom {{k_{z} } {k_{y} }}} \right. \kern-0pt} {k_{y} }}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>k</mi> <mi>z</mi> </msub> <mrow> <mfenced open="/"> <mphantom> <mpadded width="0pt"> <msub> <mi>k</mi> <mi>z</mi> </msub> <msub> <mi>k</mi> <mi>y</mi> </msub> </mpadded> </mphantom> </mfenced> </mrow> <msub> <mi>k</mi> <mi>y</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>). Owing to the differences in sensitivity of three-directional permeability to temperature and principal stresses, the anisotropy ratio exhibits complex nonlinear evolution with changing temperature and true-triaxial stress states. A new three-directional permeability model is developed by introducing variable temperature-stress sensitivity coefficients into exponential permeability formulation. This model can effectively characterize the evolution of three-directional permeability and corresponding anisotropy ratio under varying temperature and true-triaxial stress conditions.</p>

Influence of true-triaxial stress and elevated temperature on three-directional permeability of a purple sandstone

期刊论文
发表日期：

2026年4月30日

查看全文

Jiacun Liu,
Xing Li,
Yi Xia,
Ying Xu,
Dongping Liu,
Kaiwen Xia

摘要

The reservoir rocks exist within geological environments characterized by elevated true-triaxial stress, pore pressure, and temperature. Understanding the coupled effects of temperature and true-triaxial stress on three-directional permeability is crucial for the efficient extraction of underground resources. Therefore, this study employs a self-developed true-triaxial geophysical imaging cell equipped with a temperature-controlled module to conduct three-directional helium permeability tests on purple sandstone. A stepwise loading path is adopted in this study to examine the influence of temperature (from 20 to 80 °C) and true-triaxial stress on three-dimensional permeability. As a result of inherent structural heterogeneity, the three-directional permeability exhibits significant anisotropy even under isotropic stress conditions. Under the coupled effects of thermal expansion and stress compaction, the three-directional permeability decreases with increasing temperature and principal stresses, and its sensitivity exhibits a negative correlation with both temperature and stress levels. This study introduces anisotropy ratios to quantitatively characterize the anisotropy degree in three-directional permeability ( ${{k_{y} } \mathord{\left/ {\vphantom {{k_{y} } {k_{x} }}} \right. \kern-0pt} {k_{x} }}$ $k_{y} /) k_{x}$ , ${{k_{z} } \mathord{\left/ {\vphantom {{k_{z} } {k_{x} }}} \right. \kern-0pt} {k_{x} }}$ $k_{z} /) k_{x}$ , ${{k_{z} } \mathord{\left/ {\vphantom {{k_{z} } {k_{y} }}} \right. \kern-0pt} {k_{y} }}$ $k_{z} /) k_{y}$ ). Owing to the differences in sensitivity of three-directional permeability to temperature and principal stresses, the anisotropy ratio exhibits complex nonlinear evolution with changing temperature and true-triaxial stress states. A new three-directional permeability model is developed by introducing variable temperature-stress sensitivity coefficients into exponential permeability formulation. This model can effectively characterize the evolution of three-directional permeability and corresponding anisotropy ratio under varying temperature and true-triaxial stress conditions.