Accurate gas permeability measurement in ultra-low-permeability geomaterials is often affected by temperature fluctuations during long-duration pressure-decay tests, which may compromise the evaluation of gas migration and related barrier or storage performance. Existing corrections based solely on the ideal gas law address pressure–temperature coupling but neglect viscosity-related variations that distort the decay timescale. This study develops a double-calibration framework that integrates isothermal pressure calibration and effective-time scaling. The approach converts measured pressures into isothermal equivalents at a reference temperature and rescales time to account for temperature-dependent gas viscosity, thereby mapping the non-isothermal problem onto an equivalent isothermal formulation without modifying the experimental setup. Applications to long-duration gas permeability tests on saturated compacted bentonite specimens show that pressure calibration provides the dominant improvement, stabilizing fluctuating pressure–time curves, whereas time calibration contributes a smaller but systematic refinement. The maximum discrepancies between single and double calibration reach 6.41 × 10−23m2 for intact bentonite and 2.00 × 10–23 m2 for cracked bentonite, with differences most evident during strong thermal oscillations. Pointwise sensitivity analysis further demonstrates that within ± 4 °C of the reference temperature, pressure deviations reach about ± 1.35% while time corrections remain within ± 0.23%, leading to a combined pointwise permeability deviation of about ± 1.1%. However, synthetic sliding-window analysis under sinusoidal temperature histories shows that such small pointwise thermal effects can propagate into much larger permeability errors over finite fitting intervals, reaching 87.1%–258% at k = 10−21 m2 and increasing to the order of 104% at k = 10−23 m2. These results indicate that the significance of the second calibration should be evaluated in terms of propagated permeability error rather than the small pointwise effect alone, especially for ultra-low-permeability materials with k ≤ 10−21 m2. The proposed approach provides a practical tool for reliable characterization of ultra-low-permeability geomaterials under non-isothermal conditions and can, in principle, be extended to other gas permeability test procedures that infer permeability from gas pressure measurements.

A Double-Calibration Framework for Gas Permeability Measurement of Ultra-low-permeability Geomaterials Under Temperature Fluctuations

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发表日期：

2026年7月24日

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Hongyang Ni,
Jiangfeng Liu,
Zhipeng Wang,
Shijia Ma,
Wanqing Shen

摘要

Accurate gas permeability measurement in ultra-low-permeability geomaterials is often affected by temperature fluctuations during long-duration pressure-decay tests, which may compromise the evaluation of gas migration and related barrier or storage performance. Existing corrections based solely on the ideal gas law address pressure–temperature coupling but neglect viscosity-related variations that distort the decay timescale. This study develops a double-calibration framework that integrates isothermal pressure calibration and effective-time scaling. The approach converts measured pressures into isothermal equivalents at a reference temperature and rescales time to account for temperature-dependent gas viscosity, thereby mapping the non-isothermal problem onto an equivalent isothermal formulation without modifying the experimental setup. Applications to long-duration gas permeability tests on saturated compacted bentonite specimens show that pressure calibration provides the dominant improvement, stabilizing fluctuating pressure–time curves, whereas time calibration contributes a smaller but systematic refinement. The maximum discrepancies between single and double calibration reach 6.41 × 10⁻²³m² for intact bentonite and 2.00 × 10^–23 m² for cracked bentonite, with differences most evident during strong thermal oscillations. Pointwise sensitivity analysis further demonstrates that within ± 4 °C of the reference temperature, pressure deviations reach about ± 1.35% while time corrections remain within ± 0.23%, leading to a combined pointwise permeability deviation of about ± 1.1%. However, synthetic sliding-window analysis under sinusoidal temperature histories shows that such small pointwise thermal effects can propagate into much larger permeability errors over finite fitting intervals, reaching 87.1%–258% at k = 10⁻²¹ m² and increasing to the order of 10⁴% at k = 10⁻²³ m². These results indicate that the significance of the second calibration should be evaluated in terms of propagated permeability error rather than the small pointwise effect alone, especially for ultra-low-permeability materials with k ≤ 10⁻²¹ m². The proposed approach provides a practical tool for reliable characterization of ultra-low-permeability geomaterials under non-isothermal conditions and can, in principle, be extended to other gas permeability test procedures that infer permeability from gas pressure measurements.