金属套管井间电磁校正方法研究

Method of Cross-well Electromagnetic Correction in Metal Casing

从麦克斯韦方程出发,得到了井间电磁接收信号与4层介质(井眼、金属套管、水泥环、地层)参数以及接收机位置之间的解析式。模拟计算了泥浆电阻率、金属套管(位置、电阻率、磁导率)、水泥环电阻率、发射频率以及接收机位置对井间电磁接收信号的影响。由数据模拟与分析得到井间电磁与井眼介质以及金属套管之间的关系。通过分析,得出井眼内泥浆以及水泥环电阻率对接收信号的影响可以忽略;金属套管对接收机的信号影响较大。在确定金属套管的位置、厚度、电导率、磁导率、发射频率以及测量2口井的井间距大于20m时,通过建立数据库的方式对金属套管的影响进行校正。将金属套管校正后的数据与无金属套管存在的数据对比,误差小于1%。

The electromagnetic field equations in vertical stratified media are derived from the Maxwell equations, and the analytical formula about the relations between received signals, parameters of boreholes, casing, formation and the receiver position, are obtained.The impact of mud resistivity, casing position, casing resistivity, casing magnetic permeability, cement resistivity, transmission frequency and receiver position on the received signal has been simulated.And the relation of cross-well electromagnetic to borehole media and casing has been obtained through large amounts of numerical simulation and analysis.The analyzing results show that the influence of the borehole mud and cement resistivity on received signals could be ignored.Metal casing plays a significant role in received signals.When the distance of two wells is larger than 20 m, the receiving signals could be calibrated by built database while the metal casing＆#39;s position, thickness, conductivity, and permeability and transmitting frequency are determined.The difference is within 1% between the data calibrated and data without metal casing.