声电转换信号的井下观测与初步分析

Field test of acoustoelectric logging signals and preliminary analysis

声电测井是一种基于地层岩石的声电耦合效应探测的、特殊的井孔地球物理测井方法。自行研发的声电效应测井仪(AELT)在中国北部某油井进行了实际下井测试,通过使用声波信号和电信号同步采集的方式得到了该井声波发射时的声电同步接收信号,在井下观测到了声电效应测井理论所预期的伴随模式声电转换电信号和界面模式声电转换电信号。初步对比结果表明,伴随模式声电转换信号的波形组成成分以及频率特征与声波发射—声波接收信号的特征相似;在整个测量井段,纵横波信号能量与由此产生的声电信号能量相对较弱;而斯通利波信号能量与由此产生的声电信号能量相对较强,且二者随深度的变化趋势具有很高的相关性。界面模式声电转换信号到时几乎不会随源距和地层深度的变化而改变,其能量与常规测井数据之间具有很高的相关性。结合由声波信号转换出的电信号的相关特征,有可能为裸眼井地层参数评价提供新的参考依据。

Acoustoelectric logging is an unconventional well-logging method based on the seismoelectric coupling effect in rocks. The acoustoelectric logging tool(AELT) developed by our team was tested in a well located at Eastern China. We received acoustic–acoustic and acoustic–electric synchronization signals via an acoustic and electric synchronous acquisition system. Theoretically expected accompany-and interface-mode acoustoelectric signals could be observed in the measured signals. Preliminary results show that the waveform composition and frequency characteristic of accompany-mode acoustoelectric and acoustic–acoustic signals are similar. Over the entire measured well section, the energy values of acoustic P/S-waves and the accompany-mode acoustoelectric signals emitted by this wave are relatively weak, whereas the energy values of the acoustic Stoneley wave and the accompany-mode acoustoelectric signals emitted by this wave are relatively strong. A high correlation exists between the energy of the acoustic–acoustic and acoustoelectric signals in the entire measured well section. The arrival time of interface-mode acoustoelectric signals is not changed by the variation in offset and formation acoustic velocity. The energy of interface-mode is related to conventional well-logging data. Certain features of the seismoelectric transition effect are related to the permeability and porosity of a formation, and thus, AELT can potentially provide a new solution for estimating formation parameters.