Klinkenberg Effect and Effective Pressure for Gas Permeability of Tight Sandstones. Issue 2 (27th February 2019)

• Record Type: Journal Article
• Authors: Xiao, Wenlian; Bernabé, Yves; Evans, Brian; Mok, Ulrich; Zhao, Jinzhou; Ren, Xiyao; Chen, Meng
• Is Part Of: Journal of geophysical research. Volume 124:Issue 2(2019)
• Page Start: 1412
• Page End: 1429
• Publication Date: 2019-02-27
• Subjects: gas permeability -- Klinkenberg plots -- effective pressure -- pressure sensitivity -- tight sandstones; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2018JB016686
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Gas permeability k g of tight sandstones was measured while cycling pore pressure, P f, and confining pressure, P c, using two different procedures. First, we cycled the pore pressure from a minimum value close to atmospheric pressure to a maximum one slightly lower than P c, while keeping the P c constant. Second, P f and P c were simultaneously varied so as to keep the difference, P c − P f, constant. Significant effects owing to slip flow were observed when the gas pressure was lower than about 5 MPa. Klinkenberg plots showed that, under constant P c, gas permeability k g decreased linearly for high values of 1/ P f, reached a minimum and then sharply increased as 1/ P f approached zero. Under constant P c − P f, k g again decreased linearly in the high limit of 1/ P f and showed additional decrease in the low 1/ P f limit. The linear segments in both procedures indicate that k g in tight sandstones was subject to slip flow at low values of P f, while the curved segments revealed the sensitivity of permeability to effective pressure when P f became comparable in magnitude to confining pressure. The effective pressure coefficient α was estimated and generally appeared to be a well‐defined decreasing function of the pressure difference P c − P f . We modified the Walsh permeability model for fissured rocks to include slip flow effects and obtained satisfactory fits to the experimental data for the samples with the lowest porosities and the highest pressure sensitivities. This observation suggests that the intrinsic permeability of these rocks was controlled by intergranular and/or intragranular crack‐like pores. Key Points: Gas permeability was measured in the slip flow and viscous regimes at variable confining and pore pressures, P c and P f The effective pressure coefficient generally appeared to be a well‐defined decreasing function of the pressure difference P c − P f The Walsh rough crack model modified to account for slip flow gave good results for the samples with the highest pressure sensitivity