不同压力条件下部分饱和砂岩速度实验结果及理论解释

Experimental results in partially saturated sandstone under condition of different pressure and their theoretical interpretation.

在实验高频条件下,对储层砂岩样品采用常规饱和方法得到的弹性波速度随饱和度的变化呈现出复杂的样式,不同于地震勘探中用有效流体模型给出的理论结果,这种差异在低围限压力下更为明显。本文在变压力条件下,对部分饱和储层砂岩的纵、横波速度变化规律进行了系统实验研究及定量分析。研究表明,在实验高频条件下,两种不同孔隙尺度上流体分布的不均匀性明显影响实验结果,也是实验结果与有效流体模型理论值存在差异的主要原因:孔隙尺度上纵横比较小的裂隙中的饱和流体在高频条件下非“弛豫”作用对弹性波速度存在影响;较大尺度上(包含多个孔隙)孔隙流体不均匀的斑块分布对纵波速度存在影响。因此不论在实验室条件下,或是在实际地震勘探中分析弹性波速度时,应考虑这些因素影响。

Under the experimental high-frequency condition, the velocity variation of elastic wave of sandstone samples in reservoir with saturation obtained by using common saturated method appears complex pattern, which is different from the theoretical results given by effective fluid model used in seismic exploration that is more apparent in lower confining pressure. Under the pressure-changed condition, the paper conducted systematically experimental research and quantitative analysis for the variation regularity of P- and S-wave velocities of partially saturated sandstone in reservoir. The study showed that under the experimental high-frequency condition,non-uniformity of fluid distribution in two different pore scales significantly affects the experimental results,that is also the main reason that differences exist between the experimental results and theoretical values of effective fluid model: the effect of unrelaxed action of saturated fluid in the fracture with smaller aspect of pores on elastic wave velocity exists under the high-frequency condition; the non-uniform patchy distribution of pore fluid in larger scale (including several pores ) affects the P-wave velocity. It should consider the influences of these factors when analyzing elastic wave velocities either in laboratory condition or in practical seismic exploration.