Experimental and theoretical study on comparisons of some gas permeability test methods for tight rocks

Decheng Zhang, Hao Gao, P. G. Ranjith, Chengpeng Zhang, Guowei Ma

Research output: Contribution to journalArticleResearchpeer-review

4 Citations (Scopus)

Abstract

Precise gas permeability measurements of tight rocks are important for the exploration of unconventional reservoirs. Steady-state and varied unsteady-state gas permeability tests were conducted on a heat-treated siltstone. Brace’s approach ignores the sample pore volume resulting in the underestimation of sample permeability, and its discrepancy with the sample pore volume corrected permeability depends on the ratio between the sample pore volume and reservoir volumes. Permeability in the pulse-decay test (kT) is higher than that based on Brace’s approach (kB) but lower than the sample pore volume corrected permeability (kC) in the downstream pressure build-up test. It is theoretically and experimentally proved that the transient flow approach is equal to the Brace’s approach as both assume the validity of Darcy’s law and ignore the sample pore volume. Variations of the gas permeability are dominated by gas slippage and the effective stress at low and high pore pressures respectively. The apparent steady-state permeability is higher than the sample pore volume corrected permeability at small upstream pressures, while its intrinsic permeability is always lower than that of the sample pore volume corrected permeability. Both the intrinsic permeability vs. porosity and intrinsic permeability vs. the effective stress curves follow power laws, and the effective stress coefficient is higher than unity due to the clay filling and lining.

Original languageEnglish
Pages (from-to)3153-3169
Number of pages17
JournalRock Mechanics and Rock Engineering
Volume55
Issue number6
DOIs
Publication statusPublished - Jun 2022

Keywords

  • Effective stress
  • Gas slippage
  • Permeability comparison
  • Steady-state permeability
  • Unsteady-state gas permeability

Cite this