饱和砂岩滞弹性弛豫衰减机理的探索

本文采用从法国引进的Metravib热机械分析仪用正弦波加载方式,首次对四种不同孔隙度的饱和砂岩的衰减进行了实验研究,在5~400 Hz的频率,-50 ℃~100 ℃的温度范围获得衰减的热弛豫规律,由此求得它们的激活能和原子振动频率,其激活能和弛豫时间是处在原子和电子的激活能和弛豫时间之间.可见,在饱和岩石的晶粒间界缺陷处参与扩散的是原子、电子.并得出随孔隙度增大,衰减强度和激活能增大,原子的振动速率加快,弛豫时间缩短.在交变应力作用下,由多种矿物晶体胶结而成的饱和砂岩是一种多晶、多相的固体,由于内部结构复杂,损伤、缺陷广布,弛豫衰减是普遍存在的.饱和砂岩中存在的晶界、相界等许多缺陷,以及缺陷间的相互作用,比如饱和岩石中的饱和液体与岩石骨架之间的作用等等都可以产生弛豫衰减峰,弛豫过程还受晶界上原子扩散所控制.由于饱和岩石中的种种缺陷、相界等等导致上述矿物颗粒或晶界之间的多重弛豫,才使弛豫衰减峰变宽,分布宽度增大.用饱和砂岩中特有的饱和液体及砂岩内部结构的复杂性解释了饱和砂岩的衰减机理,很自然地将其宏观衰减特征与微细观结构紧紧联在一起.衰减及其机理的研究既具有科学意义,对地球物理勘探又具有实用价值.

Research of viscoelasticity attenuation mechanism of saturated sandstones

In this paper,the attenuation of saturated sandstones with four different porosities has been firstly studied experimentally in the role of sine wave caused by thermo-mechanical analysis equipment named Metravib from France.According to the characteristics of relaxation attenuation peak,saturated liquid,and complex inner structures of saturated sandstones,the attenuation mechanism has been explained and the macroscopic features and the micro-structures are naturally linked.Under the sine wave stress,saturated sandstone cemented by a variety of mineral crystals is a kind of polycrystalline,multiphase solids with complex inner structures and widespread defects,and relaxation attenuation is a common phenomenon.There are many factors affecting this phenomenon,such as the sliding friction between mineral particles,the re-distribution of point defects,dislocations,grain boundaries on the outside stress effect,the interaction of dislocations themselves or between dislocations and point defects,the interaction of the saturated liquid and the rock matrix and so on.Moreover,the process of the relaxation is also controlled by the atomic diffusion.Because of the existence of defects,phase boundaries and so on,multiple relaxation is turned out between mineral grains and grain boundaries,which makes the width of relaxation attenuation peak broader.The activation energy and the vibration frequency of electronic and atomic of pump oil saturated Pengshan sandstone and Arkose also are attained,and the analysis results show that activation energy and relaxation time of above-mentioned two kinds of sandstones are matched with that of electronic and atomic.It is visible that it is atoms and electrons of solids that are involved in the places of grain boundary defects of saturated rock,more likely to be liquid atoms,and it is found that with the increase of porosity,activation energy and the attenuation degree increase and relaxation time decreases.The research of attenuation and its mechanism has both scientific significance and practical value to geophysical exploration.