利用周期振荡法测试超低渗储层的渗透率

渗透率是储层最重要的物性参数，也是油气开发的基础。随着页岩气、致密砂岩油气等非常规油气的开发，迫切需要开展超低渗透率（<0.1×10-3 μm2）测试，对测试方法和仪器都提出了挑战，是非常规油气开发研究的难点。目前我国石油工业中主要采用稳态法和脉冲衰减法进行超低渗透率测试，在测试精度、稳定性和测试周期方面还存在不足，探索高精度超低渗透率的方法十分重要。分析了室内渗透率测量的稳态法、脉冲衰减法和周期振荡法3种方法原理，在三轴应力下进行了岩石超低渗透率对比测量。结果表明，相比稳态法和脉冲衰减法，周期振荡法具有稳定性好、精度高、用时短的优点，建议引入非常规超低渗透储层渗透率测试。对周期振荡法的设备要求和数据处理方法进行了讨论，提出采用快速富里叶变换（FFT）、互谱法等信号处理方法提高数据信噪比，提高超低渗透率的测试精度和稳定性。

Ultralow permeability measurements with periodic oscillation method

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.