A robust data processing method for pulse-decay measurement of tight materials

The pulse-decay method is a widely-adopted transient technique for measuring the permeability of tight materials. Given that the gas pressure within the pulse-decay apparatus during the measurement is much higher than atmospheric pressure, gas leakage is usually inevitable, more or less, which may potentially introduce significant errors in the permeability measurements. The data is always discarded and unpublished once a leakage is remarkable. There lacks reasonably explained and conveniently applicable approach for data processing at present. This study proves that the data with slight gas leakage during measurements are still useful and recover the correct value of permeability. To achieve that, a mathematical model accounting for gas leakage is developed and solved. The analytical solution unveils that when gas leakage is present, the logarithm of bilateral pressure difference deviates from a straight line, which depends on the leakage rate and the size of the two chambers. A new data processing method for calculating permeability is proposed by using the unilateral pressure difference over a given time interval. The method corrects the permeability by eliminating the redundant term due to leakage in the analytical solution and is validated by experimental data. The applicability and reliability of pulse decay measurement data will be significantly enhanced.