引用本文
张博, 唐晓明, 苏远大, 祁晓. 2016. 一种利用双源反激的随钻声波测井方法. 地球物理学报, 59(3): 1151-1160, doi: 10.6038/cjg20160335
ZHANG Bo, TANG Xiao-Ming, SU Yuan-Da, QI Xiao. 2016. An acoustic logging while drilling technique using the dual source of opposite polarity.
Chinese J. Geophys. (in Chinese), 59(3): 1151-1160, doi: 10.6038/cjg20160335
一种利用双源反激的随钻声波测井方法
1. 中国石油大学(华东)地球科学与技术学院COSL-UPC声学测井联合实验室, 青岛 266580;
2. 中国电波传播研究所, 河南 新乡 453003
收稿日期: 2014-11-20 2016-01-12 收修定稿
基金项目: 国家自然科学基金(41474092)资助.
作者简介: 张博,男,1982年生,在读博士,研究方向是声波测井理论、方法与技术.E-mail: zhangbo_upc@163.com
通讯作者: 唐晓明,男,1955年生,教授,多年来一直致力于地球物理(特别是声波)测井、岩石物理学、地震波传播及测量等方面的研究和技术开发工作.E-mail: tangxiam@aliyun.com
摘要: 随钻单极子纵波测井时存在很强的钻铤波的干扰.针对这一问题,提出了一种双源反激随钻声波测井方法,从数据采集环节对钻铤波进行压制;在后续数据处理中结合声波干涉法,从而实现一种无需隔声装置的随钻声波测井方法.理论模拟表明双源反激方法可以有效压制钻铤波,地层波的信噪比也能得到相对增强.对钻铤波压制后的数据进一步用声波干涉法处理可以从中提取地层纵波信息.设计了实验样机,并在空气中进行了实验.结果表明不同工作频率下该方法对钻铤波均有明显的压制效果,即使在5 kHz低频情况下钻铤波也能压制到原来的25%.验证了该方法的可行性.应用该方法的好处是可以避免对钻铤强度的破坏,并能扩展现有随钻声波测井仪纵波测量的工作频带范围.
关键词:
双源反激方法
随钻声波测井
钻铤波压制
隔声技术
声波干涉法
An acoustic logging while drilling technique using the dual source of opposite polarity
ZHANG Bo
1,2, TANG Xiao-Ming
1, SU Yuan-Da
1, QI Xiao
1
1. COSL-UPC Allied Borehole Acoustic Laboratory, School of Geosciences and Technology, China University of Petroleum, Qingdao 266580, China;
2. China Research Institute of Radiowave Propagation, Henan Xinxiang 453003, China
Abstract: During monopole acoustic logging while drilling(LWD), there is a strong tool wave propagating along the drill collar, which, when recorded by the receivers on the LWD tool, strongly interferes with the elastic wave from the surrounding formation and adversely affects the measurement of formation elastic wave velocity. Existing LWD acoustic technology suppresses the tool wave by building an isolator along the collar using groove cutting techniques, which often results in reduction of the tool's mechanic integrity. This study proposes a new technique to solve the tool wave problem in the LWD acoustic measurement. This technique uses the dual source of opposite polarity to enhance the Signal to Noise Ratio of the formation wave signal.Two identical acoustic sources having opposite excitation polarity are placed along the LWD tool, with respective source-receiver distances. The source with longer distance is first fired, exciting elastic wave propagating in the formation and tool wave propagating along the collar. When the tool wave arrives at the second source, the source is actuated, exciting another tool wave with opposite polarity. By this firing scheme, the tool wave along the drill collar can be largely suppressed. Numerical simulation shows that the tool wave can be removed if the wave's dispersion effect is minimal. In the presence of significant wave dispersion, the tool wave after suppressing may still exist, but the much reduced tool-wave amplitude allows for obtaining the formation elastic wave velocity using a wave interference method in the subsequent data processing. To prove the concept of using dual source in LWD, an experimental LWD model was built and a laboratory experiment was conducted. Various excitation frequencies, ranging from 5 to 16 kHz, were used and the waveforms excited by the dual source system were measured. The results show that the collar wave can be suppressed for different working frequencies. Even down to 5 kHz frequency, the collar wave can be reduced to 25% in the experiment condition. Both the theoretical modeling and experiment results demonstrate the feasibility and practicality of the proposed technique. Compared with the traditional LWD technique, the dual source technique removes the need for sound isolation and therefore maintains the mechanic integrity of the tool. Besides, by suppressing tool wave from low to high frequencies, the new technique can operate in a broad frequency range for the LWD acoustic measurement.
Key words:
Dual source of opposite polarity
Acoustic logging while drilling
Collar wave suppressing
Sound isolation
Wave interference method
1 引言
最近十几年,随钻声波测井技术发展迅速,显示了很好的应用前景(唐晓明和郑传汉,2004).然而钻铤的隔声问题,即消除钻铤波对地层波测量的强烈干扰,一直是该技术的一个难题(崔志文,2004;唐晓明和郑传汉,2004;苏远大等,2011;王兵等,2012).Tang等(2002)指出在随钻环境下采用四极子声源,当工作频率低于钻铤波截止频率时,地层横波不受钻铤波的影响,不需要专门的隔声装置.因此对随钻 隔声的研究主要是针对随钻单极子纵波的隔声问题.
目前市场上商业化应用的随钻声波测井仪隔声方式均是采用在钻铤上刻槽的方法,如威德福ShockWave、哈里伯顿BAT/QBAT、贝克休斯APX(Freitag et al.,2004)、斯伦贝谢SonicVision(Alford et al.,2005)、斯伦贝谢SonicScope(Kinoshita et al.,2010; Alford et al.,2012). 尽管其刻槽方式各不相同,但均是以牺牲钻铤强度为代价来获得一定的隔声效果.测井科研人员一直在寻找一种对钻铤强度破坏小、甚至无破坏的隔声技术.唐晓明等(2012)、Su等(2012;2015)提出了一种在钻铤上变径隔声的随钻声波测井方法,利用拉伸波在钻铤中存在固有阻带的现象,对不同横截面的钻铤进行组合使组合后的阻带得到拓展,这种组合式的隔声方式降低了对钻铤强度的破坏.Zhan等(2005;2006)提出基于震电效应原理的随钻声波测井技术,来解决钻铤的隔声问题.但目前该方法的工业化应用还面临很多困难.王华等(2009)提出在信号处理环节将钻铤波减掉的方法,但这种方法需要用刻槽钻铤和不刻槽钻铤实际测量数据进行标定.
对于装置在钻铤上的随钻单极子声波测井仪器来说,如果钻铤不做隔声,声波信号采集量化时电路的增益将被较大幅度的钻铤波所控制,这样采集的地层声波信号的信噪比较低,很难准确提取到地层的声速.本文提出采用双源反激方法,在数据采集过程中对钻铤波进行压制从而提高地层波的信噪比;在后续数据处理上采用声波干涉法来进一步消除钻铤波的干扰,从而形成一种无需隔声装置的随钻声波测井技术.
2 基本原理
如图 1所示,该方法采用两个发射,分别是远发射Tf和近发射Tn,二者在钻铤轴向的间距为D.测井时,Tf首先激发,发射幅度为A1,Tn延时一段时间τ之后激发(发射时序见图 2),发射极性与Tf相反,发射幅度为A2.在双源发射的同时,对接收器阵列(R1,R2,…,RN)上的信号进行采集并记录.通过选择合适的参数A1、A2及τ,使得在接收器的位置上Tf和Tn 所激发的二钻铤波同时到达,但极性相反、幅度相当.这样,接收波形中的钻铤波相互叠加后相消,即钻铤波得到压制.而对于接收波形中Tf和Tn产生的地层信号,只要地层波和钻铤波速度存在差异,其到达接收器的时间就不一致,相互叠加后仍能保留.相对于钻铤波,地层波就得到了增强.对于给定钻铤,钻铤波的波速是固定和已知的.因此,在双源激发过程中,只要固定发射间距并选取适当的延迟时间,即可实现压制钻铤波的隔声效果,达到不用隔声装置来进行隔声的目的.