岩芯纵波时差稳态测量方法  

A steady-state measurement method of core p-wave slowness

作　　者：沈建国[1] 盛晓斐[1] 皮光玉 李山生[2] 

机构地区：[1]天津大学功率超声实验室,天津300072 [2]胜利测井公司,东营257096

出　　处：《地球物理学进展》2014年第5期2246-2250,共5页Progress in Geophysics

摘　　要：声波测井的频率主要分布在1-6kHz和15-25kHz范围内,实验室采用对穿法测量岩芯声波时差的频率一般分布在500kHz到2 MHz,两者频率相差很大.砂岩储集层是孔隙介质,其流体与骨架相互作用后导致其纵波速度随频率改变.这样,上述两种测量方法所得到的声波时差会有比较大的差别.随着研究的深入,人们开始利用砂岩纵波速度随频率的变化曲线识别孔隙流体类型.为此,需要在实验室内测量岩芯在15-25kHz范围内的声波时差.根据纵波在有限长一维自由杆中传播时的固有频率,本文设计了一种测量岩芯声波时差的新方法,该方法采用冲击方法产生振动,通过测量振动系统稳定以后的频率获得岩芯的声波时差.这种方法所测量的声波时差的频率与声波测井的频率接近.并且通过调整岩芯长度,可以获得不同频率的声波时差,即频散曲线,为深入研究孔隙介质中流体类型对声波传播特征的影响提供了新的手段.The frequency distributions of sonic logging are mainly in the range of 1-6kHz and 15-25kHz.The method adopted in laboratory to measure sonic wave slowness in cores is transportation,it＇s frequency distribution is generally between 500 kHz and 2 MHz.The difference in frequency is quite lager.Sandstone reservoir is porous media.Velocity of Pwave changes with frequency after the interaction of fluid in sandstone reservoir and the frame.So the differences in sonic wave slowness obtained by the two methods are relatively large.With further research,the sandstone P-wave slowness curve changing with frequency has been used to identify the type of pore fluid.Therefore,sonic wave slowness of core in the frequency range of 15-25kHz has to be measured in laboratory.A new method of measuring the sonic wave slowness of core is put forward in this paper,according to the natural frequency of Pwave propagating in one-dimensional free bar of finite length.In this method,vibration is generated by impacting.The sonic wave slowness of core is obtained by measuring the frequency of the vibrating system when it＇s steady. What＇s more,by adjusting the length of core,sonic wave slowness of different frequency can be obtained,namely dispersion curve.This provides a new method to study how the fluid type affects the wave propagation characteristics in the porous media intensively.

关 键 词：声波时差 岩芯 波长 固有频率 冲击 

分 类 号：P631[天文地球—地质矿产勘探]