Abstract: Permeability is one of the most important parameters required for reservoir evaluation, well production calculation and developing a reasonable development program. Obtaining the accurate permeability is helpful for effectively exploiting tight petroleum reservoirs. Due to the shortcomings of conventional steady-state permeability measurement method such as long experimental process and easily affected by the environmental temperature, this paper has conducted comparative study of permeability of 39 block rocks of tight reservoir using both steady-state and unsteady-state techniques. Meanwhile, those factors which affecting experimental results accuracy have also analyzed including permeability, experimental operation method and the way of combination of effective stress. The experimental results show that the unsteady-state pulse transient decay technique consistently underestimates the steady-state Klinkenberg-corrected permeability. Pulse decay permeability is only about 47.26% of the steady-state permeability in average. The difference between the above two different kinds of permeability increase with the decrease of the rock samples permeability. Error analysis suggests that the high effective about 9 MPa loaded on the rock sample before the pulse decay permeability measurement and the combination of high confining stress and high pore pressure can induce a portion of experimental error, but still not fully explain the overall error between the pulse decay permeability and the steady-state Klinkenberg-corrected permeability. Finally, mathematical fitting result shows that the relative error and the pulse decay permeability has a good logarithm function.

Key words: permeability, tight reservoir, steady flow, unsteady flow, pulse decay technique, operation method, effective stress