摘要
随着石油勘探开发需要的转变,随钻测井技术的地质导向功能正受到越来越多的使用.本文利用各向异性水平层状地层中的磁流源并矢Green函数对定向随钻电磁波电阻率测井仪器的地质导向方法进行了研究.利用由接收线圈的电压定义的导向向量对低阻围岩的指向性并结合定向地质导向信号的变化,可以确定仪器与地层界面的相对位置.对定向数据进行方位成像可以得到地层方位和井斜角的相关信息,并且不受地层各向异性的影响.数值模拟结果表明:线圈距越长,仪器的探测范围越远且成像的对比度越大;频率越高,目的层与围岩层的电阻率对比度及井斜角越大时,成像的对比度也越大,但井斜角越大,定向信号发生明显变化的深度区间会越窄.利用单界面模型的定向地质导向信号制作出的交会图版可以使用插值法估计仪器到界面距离.所得结果为定向随钻电磁波电阻率测井仪器的地质导向方法提供了参考.
The geo-steering service provided by logging-while dri!ling technology is being more widely used with requirement of petroleum exploration and production being changed. In this article, the geo-steering method of directional electromagnetic wave resistivity logging-while-drilling tools was studied using the magnetic-current-source dyadic Green＇s functions for horizontally stratified anisotropic media. The relative position between tool and formation boundary can be fixed by combining the orientation vector and the variation of directional geosignal, so as to eliminate the ambiguity, lower the probability of making wrong drilling decisions and place the borehole in optimal position. The orientation vector is derived from the receiver coil＇s voltage and points to the conductive shoulder bed, in addition, a superposition method is applied to calculate Green＇s functions in formation model with tilted boundary which is commonly encountered in underground scenarios. The information related to formation azimuth and dip can be obtained by using the azimuthal imaging of directional data, which is symmetrically compensated and free of influence exercised by formation anisotropy. Numerical results illustrate that the investigation depth and the contrast of image will increase with increasing coil spacing. The contrast of image will increase with increasing frequency and resistivity contrast between target bed and shoulder bed as well as dip angle, but the depth interval in which directional signals change significantly will narrow with increasing dip angle. The tool-to- boundary distance can be estimated by interpolating real time date into the crossplot of directional geosignal calculated by single boundary model. However, when shoulder bed resistivity is known prior to drilling, the application range of the crossplot made by two directional geosignals is severely limited, besides, the directional geosignals lost the sensitivity to tool-to-boundary distance when the transmitter coil and receiver coil are separated by formation boundary. It＇s necessary to develop some more powerful techniques to overcome the oversimplification of crossplot calculated by single boundary model and to deal with more complex underground structure better. The azimuth and distance of the boundary which has not been penetrated can be obtained by integrated utilization of above methods, and then according this, the well trajectory can be adjusted in real time to achieve optimal wellbore placement. These conclusions provide reference to the geo-steering method of directional electromagnetic wave resistivity logging-while-drilling tools.
出处
《地球物理学进展》
CSCD
北大核心
2014年第1期462-469,共8页
Progress in Geophysics
基金
教育部新世纪优秀人才支持计划(NCET-10-0767)资助
关键词
电磁波电阻率
定向随钻测井
地质导向
地层界面
并矢Green函数
electromagnetic wave resistivity
directional logging-while-drilling
geo-steering
formation boundaries
dyadic green＇s functions
