页岩各向异性参数间关系及其影响因素分析

Correlation of shale anisotropic parameters and their influence factors

纵波及横波各向异性参数ε和γ是表征页岩各向异性特征的重要参数。通过相关实验数据,分析不同围压、干燥及盐水饱和条件下页岩各向异性参数间相关性,并通过线性回归建立ε和γ间的经验公式,为两者间相互预测或测试提供参考标定值。研究表明,随围压增大,ε和γ值均减小,且ε减小趋势更大;不同围压条件下,ε和γ值之间存在较好的线性相关性。同一页岩样品在干燥和盐水饱和条件下,ε和γ都具有很好的线性相关性。此外,通过相关实验测量数据交会,分析页岩纵横波速度比(V_P/V_S)值与干酪根之间的关系;干酪根含量较低(小于0.10)时对应V_P/V_S值随干酪根含量的增大而急剧下降;而干酪根含量相对较高(大于0.15)时,对应的V_P/V_S值几乎全部小于1.65,因此V_P/V_S值小于1.65可能是高干酪根含量的一个重要特点。

Thomsen parametersεandγare the critical parameters for shale anisotropy characterization.Based on relevant experiment data,we do some researches on the relationship between these anisotropic parameters under different conditions such as dry and brine saturated,and different confining pressure. We establish corresponding empirical formula betweenεandγbased on the linear regression of their correlation.This is useful for estimating one parameter from the other,or offering reference calibration value for the measurement.Under the conditions of different confining pressures,S-wave anisotropy and P-wave anisotropy have good linear relationship.Bothε andγ decrease with confining pressure increase andε decreases quicker.Besides,shale anisotropy parameters under the condition of dry and brine saturated have also the linear relationship.Furthermore,based on the analysis of pertinent data,we concluded that the V_P/V_S ratio will decrease sharply with Kerogen content increase when Kerogen contents is less than 0.1. While Kerogen content is more than0.15,almost all the V_P/V_S ratio are less than 1.65.So high Kerogen content may be a good reason when V_P/V_S ratio is less than 1.65.