单极源钻铤波传播机制的实验研究2

随钻情况下准确测量地层的纵波速度是当前声波测井领域亟待解决的技术难点之一,本文则针对地层纵波速度的随钻测量问题,在实验室内进行了缩小模型的随钻声波测井实验研究.首先,针对无限大流体模型,记录不同声源频率下单极源钻铤波的时域波形,研究钻铤内外两区域钻铤波的传播规律,定量分析这两部分钻铤波的频率响应特性.结果表明,随着声源激励频率的逐渐提高,钻铤波幅度呈现出先增大后减小的趋势,且中心频率两侧钻铤波幅度的变化规律不同.之后,针对小尺寸砂岩井孔模型,进行单极源随钻声波测井实验测量,进而比较两种模型下钻铤波的幅值差异性.最后,基于随钻声波测井原理和钻铤波的能量分布规律,提出一种地层纵波速度的提取方法,并进一步利用实测数据验证方法的可行性.结果表明:即使在钻铤不刻槽的情况下,通过能量剔除的方式亦可极大削弱测井全波中钻铤波的幅度,从而实现对地层纵波速度的准确测量.

Experimental studies on the mechanism of monopole acoustic collar wave 2

To accurately detect the P-wave velocity is very important in acoustic logging while drilling(LWD)measurements,but it is hard to be performed from the recorded LWD signals because of the influence of strong collar waves.Therefore,we conduct experimental studies on the properties of acoustic LWD signals in the laboratory,and focus on the measurements of P-wave velocity in this paper.Firstly,we measure the monopole inner and outer collar waves in an infinite fluid model,then quantitatively study the frequency response of the collar waves excited by different source frequency.The results show that both the inner collar wave and the outer collar wave become stronger at low frequency region,then become weaker at high frequency region,as the source frequency increases gradually.However,the rate of the change varies for the inner and outer collar waves.Secondly,we carry out experimental measurements of the monopole acoustic LWD in a small-size sandstone borehole model,and analyze the amplitude differences of the collar waves between these two models.The results indicate that the inner collar wave is the main contribution in the full waveform of LWD measurement.Finally,we propose a method for extracting P-wave velocity based on the distribution of collar wave energy,then verify the feasibility of the method with the experimental data.The results indicate that subtracting the inner collar wave from the full waveform of LWD signal can effectively reduce the influence of the collar wave on P-wave.Therefore,the P-wave velocity can be measured accurately after data processing,even if the detector is not grooved.Our results suggest a meaningful method for detecting the P-wave velocity in the field measurements.