|Title||Klinkenberg Effect and Effective Pressure for Gas Permeability of Tight Sandstones|
|Publication Type||Journal Article|
|Year of Publication||2019|
|Authors||Xiao, W, Bernabe, Y, Evans, B, Mok, U, Zhao, J, Ren, X, Chen, M|
|Journal||Journal of Geophysical Research: Solid Earth|
|Pagination||1412 - 1429|
Gas permeability kg of tight sandstones was measured while cycling pore pressure, Pf, and confining pressure, Pc, 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 Pc, while keeping the Pc constant. Second, Pf and Pc were simultaneously varied so as to keep the difference, Pc − Pf, 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 Pc, gas permeability kg decreased linearly for high values of 1/Pf, reached a minimum and then sharply increased as 1/Pf approached zero. Under constant Pc − Pf, kg again decreased linearly in the high limit of 1/Pf and showed additional decrease in the low 1/Pf limit. The linear segments in both procedures indicate that kg in tight sandstones was subject to slip flow at low values of Pf, while the curved segments revealed the sensitivity of permeability to effective pressure when Pf 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 Pc − Pf. 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.
|Short Title||J. Geophys. Res. Solid Earth|