基于ACF-AMDF的气井环空液面回波特征提取方法

为了精确有效地提取声波法检测气井环空液位的回波周期，在分析环空中测试波的传播特征及基音周期检测的基础上，提出1种基于检测信号短时自相关函数(ACF)及平均幅度差函数(AMDF)的液面回波周期提取方法；利用自主搭建的室内模拟实验系统开展了不同初始环空压力下环空液位检测实验；对检测信号进行中心削波处理并计算ACF/AMDF，提取出液面回波周期并与理论计算值对比分析；同时分析了现场环空液位检测信号，提取其回波周期。研究结果表明:提出的新方法能有效地用于提取环空液面回波周期；室内实验中，该方法最大误差绝对值为1.54%；该方法能够有效抑制液面回波信号中的随机噪声及接箍反射波等，处理后的信号曲线在回波周期处峰值更加突出、集中，而在其他位置更加平滑，提高了对液面回波周期特征的辨识能力。

Method of extracting echo characteristics of annular liquid level in gas well based on ACF-AMDF

In order to accurately and effectively extract the echo period when measuring the annular liquid level in gas well by the acoustic wave method, a method of extracting the echo period of liquid level based on the short time auto correlation function (ACF) and the average magnitude difference function (AMDF) of detection signals was put forward on the basis of analyzing the propagation characteristics and pitch period detection of the testing wave in the annulus. The experiments of annular liquid level detection under different initial annulus pressures were carried out by using the self developed laboratory simulation experimental system. The center clipping processing was conducted on the detection signals, and the ACF/AMDF were calculated, then the echo period of liquid level was extracted and compared with the theoretical calculation value. Meanwhile, the on site detection signals of annular liquid level were analyzed, and the echo period was extracted. The results showed that the proposed new method could be used to extract the echo period of annular liquid level effectively. The absolute value of the maximum error by this method in the laboratory experiments was 1.54%. The random noise and coupling echo of the echo signals of liquid level could be effectively suppressed by this method, and the signal curve after processing had the more prominent and concentrated peak value at the echo period, while smoother at other positions, which improved the identification ability of the echo period characteristic of liquid level.