Measurement of ultralow permeability

A permeability measurement method based on perturbed pressure decay between a source and a sink communicating through a porous medium is formulated. Nonideality of gas as well as corrections due to adsorption are considered. The method allows us to infer permeability at a given rock and fluid state. The accuracy of the method may be evaluated through comparison with theoretical decay characteristics and its modal amplitudes. A quantitative evaluation of the experimental inference is therefore possible. Based on the pressure decay theory, an apparatus built in our laboratory for measuring permeability is presented. As a secondary output, data analysis also provides porosity. The lowest permeability that the present apparatus is capable of characterizing is about 0.3 nm 2 , and with additional improvements, capability down to 0.05 nm 2 is anticipated. Where a steady‐state permeameter is pragmatic, excellent agreement between the two measurements is showed, validating the method. Measurements in synthetic samples also show that the method is accurate. Porosity data from a standard helium pycnometer confirm the porosity obtained from the decay method. © 2015 American Institute of Chemical Engineers AIChE J , 62: 1278–1293, 2016