基于油套环空声场特性的复杂油井动液面测量方法研究

It is important to measure the depth of dynamic liquid level of oil well in order to set reasonable oil extraction technology. Generally, echometer is used to obtain the depth of dynamic liquid level. However, it is difficult to realize that in complicated situation such as deep well, low-pressure well and non-pressure well since there’s extream weak or no echo signal. Acoustic theory shows that the tubing length associated with the resonance frequency of the air. Therefore, a novel approach that is based on acoustic field characteristic of string has been proposed to measure the depth of dynamic liquid level of oil well. It is preliminary proven to be effective by experiments on multiple experimental equipments. However several issues need to be paid attention to, i.e., 1) for deep well, low-pressure well and non-pressure well, acoustic energy attenuates severly because regualr acoustic emission devices is not powerful enough; 2) regular acoustic field models is difficult to apply due to that the nonuniform distribution of medium denstity, temperature and pressure under the well. To establish the method for measuring dynamic liquid level of complicated oil well upon the relation between depth and frequency, we first sutdy the way producing continuous low-frequency acoustic source in order to solve the problem regarding the propagation of acoustic energy. Then, by analyzing the acoustic field characteristic of tubing-casing annular space and the influence of medium density, temperature and pressure on progagation model, we will build the acoustic propagation model and air resonance model for tubing-casing annular space, based on which the depth of dynamic liquid level is obtained. The novel method proposed for measuring dynamic liquid level based on acoustic field characteristic of tubing-casing annular space provids new inspiration of measuring dynamic liquid level for complicated oil well.

测量油井动液面深度对制定合理的采油工艺具有重要意义。油田一般使用回声仪获得动液面深度，但在深井、低压井和无压井中回波信号微弱甚至没有，使得复杂油井动液面测量非常困难。声学理论表明：管内空气柱共振频率可反映管柱的长度。课题组由此提出基于管柱声场特性的油井动液面深度测量思路，并设计多种实验装置开展验证研究，初步证实可行，但发现：对深井、低压井和无压井将出现声波能量衰减严重，常规发声装置能量不足；井下介质密度、温度、压力呈非均匀分布，一般声场模型难以适用等问题。为建立复杂油井动液面的深度-频率关系检测方法，首先研究连续低频声源发生方法，解决井下声波传播能量问题；分析油套环空声场特性，研究气体成份、介质密度、温度、压力等因素对传播模型的影响，建立油套环空内声波传播模型和空气共振模型，从而计算动液面深度。本课题提出的基于油套环空声场特性的动液面测量方法，可为复杂油井的动液面测量提供新的思路。

测量油井动液面深度对制定合理的采油工艺具有重要意义。油田一般使用回波法获得动液面深度，但由于井下环境复杂噪音干扰大，回波信号微弱甚至没有，使得油井动液面测量精度较低。项目围绕油井动液面测量中的关键问题开展研究，提出一种基于油套环空空气共振的油井动液面测量新方法。.本项目在以下四个方面取得了进展：（1）为解决油井动液面测量中声音衰减问题，提出了一种低频连续白噪声声源产生方法。采用线性同余法产生两组均匀随机噪声序列，对其进行白化得到白噪声序列，然后利用Box-Muller变换算法将两组白噪声序列变换为高斯白噪声序列，最后通过窗函数带通滤波器得到理想频段的噪声序列。通过连续不断补充低频白噪声以确保油套环空空气共振。（2）通过大量实际油井声速数据，拟合了油井声速传播速度，分析油井声速传播特点和规律，从而建立油井声速传播模型，以反映某一区域内油井声速变化规律，提高油井动液面测量中声速估计的精确性；（3）研究油井管柱长度与声场固有频率之间存在确定的关系，建立了油井动液面深度与油套环空空气共振频率的数学关系，提出共振谐波频率差估算油井动液面的新方法。利用共振谐波的Welch 功率谱估计、短时傅立叶变换和FFT变换求取谐波频率差，为动液面测量新方法提供了理论支持；（4）为进一步准确读取谐波频率差，提出一种噪声干扰下离散频谱迭代插值FFT校正算法，利用两谱线插值FFT计算谱线，极大地消除了谱线定位错误影响，避免因最高谱线或者次高谱线定位错误导致的校正误差突然增大的现象，提高了油井动液面测量精度。.本课题提出的基于油套环空声场特性的动液面测量方法，可为解决复杂油井的动液面测量问题提供新的思路。