Ultra-low permeability estimation is still one of the highly relevant subject of modern petrophysics and shale-oil industry. Popular unsteady-state gas filtration laboratory methodic are not able to provide precise and unique permeability value because of algorithms complexity. Again the need to estimate sample porosity before permeability evaluation makes test protocol time consuming, too. From other hand steady-state gas filtration is classical for conventional reservoir but becomes unpractical when one use it to evaluate ultra-low gas permeability because of huge test duration and enormous result’s sensibility to temperature stability. New method and apparatus for fast and precise ultra-low steady-state gas permeability estimation based on a simple analytical solution is presented in the paper. New approach to the gas discharge evaluation allows to estimate core plugs permeability in the range from 10-5 μm2 to 10-18 μm2 with high confidence. It is important that plugs may be affected by confining pressure up to 70 MPa. Good correlation was achieved by comparison the results of gas permeability determination by new method and by modified pressure pulse decay method in plug’s permeability range from 10-5 μm2 до 10-9 μm2. New approach allows to apply confining pressure up to 70 MPa to the plug preventing gas filtration along the artificial micro fractures. Practical application of the new method to the Bazhen Fm shale and it’s lithological analogues is demonstrated in the paper.
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