Abstract: Reservoir permeability is a most important physical parameter. It is also the basis for the development of oil and gas. In recent years because of the shale gas, tight sand gas and other unconventional oil and gas development, the need for ultralow permeability (<0.1×10-3 μm2) measurement is increasing. However, the test methods and instruments are challenging, which is difficult for the development of unconventional oil and gas research. At present, China mainly uses pulse decay method for ultralow permeability testing in oil industry. The test accuracy, stability, and test cycle of pulse-decay method are still insufficient. It is very important to explore high-precision ultralow permeability method. This paper presents and analyzes the steady-state method, pulse-decay method and periodic oscillation method to measure permeability in the laboratory. The contrast application in ultralow permeability measurements are also made in an example rock with the three methods. The results show that compared to the steady state and pulse decay method, periodic oscillation method has good stability, high accuracy and short time. We propose to apply the oscillation method for ultralow permeability tests. In this paper, the equipment requirements and data processing methods of periodic oscillation method are also discussed. Fast Fourier transform (FFT), cross spectral method and other signal processing methods are introduced to improve signal to noise ratio. That is to improve the accuracy and stability of ultralow permeability measurement.

Key words: permeability；ultralow permeability；pulse decay method, periodic oscillation method, test method