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为了在较宽频域内研究砂岩衰减变化,实验在13.2MPa的初应力水平下,测得了蠕变(1小时~3天)和超声波(470 KHz、700KHz)频率下干燥的大庆、紫蓬山砂岩衰减.发现蠕变衰减随蠕变时间增大而增大,且均大于超声波频率下的衰减,最小相差亦有40%.将衰减与应力作用频率关系转化为衰减与蠕变量关系后,二者线性相关,相关系数大于95%.且据此将蠕变量向超声波频率对应的应变量外推所得的衰减值与实验测得的衰减值符合较好.实验得到的应变量与衰减的线性关系,解释了已有的0.1~1 MHz下衰减近似常量的事实,亦可预测岩石从蠕变破裂所对应的最低频率到MHz频率范围内衰减变化.
In order to study the change of sandstone attenuation in a wide frequency range, the dryness of Daqing and Zipengshan sandstone at creep (1 hour ~ 3 days) and ultrasonic (470 KHz, 700KHz) frequency was measured under the initial stress level of 13.2MPa It is found that the creep attenuation increases with the increase of creep time and both of them are larger than the attenuation under ultrasonic frequency with the minimum difference of 40% .When the relationship between attenuation and stress is transformed into the relationship between attenuation and creep, Linear correlation, the correlation coefficient is greater than 95% .Accordingly, the attenuation value extrapolated from the creep amount to the ultrasonic frequency is in good agreement with the experimentally measured attenuation value.Experimental linear relationship between strain and attenuation , Explains the fact that there is an approximate constant of attenuation at 0.1 ~ 1 MHz, and also predicts the change of rock attenuation from the lowest frequency corresponding to the creep rupture to the attenuation frequency in the MHz range.