井间电磁成像系统发射和接收同步测量应用研究

井间电磁成像利用低频电磁波对两井或多井之间进行多点扫描,测量出电磁信号经过地层产生的相位变化和幅度衰减情况,反演得到地层电阻率信息.相位反映地层电参数以及位置的敏感性要优于幅度信息.在进行相位测量时,必须保证在同一时刻对发射监测信号和接收信号进行采集.针对发射和接收系统精确同步测量方法展开研究,提出使用GPS时钟接收机在两口井各自地面系统产生同步时钟信号,把同步时钟信号通过电缆传送到井下,井下通过PLL锁相同步电路和频率补偿电路,完成井下工作主频时钟源的建立,达到地面和井下同步目的.在发射地面和接收地面设置有数传电台,相互之间可传送指令,与同步时钟结合起来,实现井下发射监测信号和接收信号的同步采集.经过测试井间电磁成像发射和接收系统同步误差≤±100 ns.

Applied Research on synchronous measurement of transmitter and receiver of cross-well electromagnetic tomography system

In cross-well electromagnetic tomography,low frequency electromagnetic waves are used for multi-point scanning between two wells or multiple wells to measure the phase changes and amplitude attenuation generated by electromagnetic signals through strata,thus inverting the resistivity information of the strata.The sensitivity of phase to reflect the electrical parameters and position of the formation is better than the amplitude information.When the phases are measured,the transmitting and receiving signals must be acquired simultaneously,In this paper,the accurate synchronous measuring method is explored for transmitting and receiving system.GPS clock receivers are applied to generate synchronous clock signals from the ground systems of two wells,and the signals are transmitted to the downhole through cable.Down the well,PLL phase locked synchronous circuit and frequency compensation circuit are adopted to establish the clock source of downhole basic working frequency,and the synchronous purpose of the ground and the downhole is achieved.Installed on the launching transmitting ground and receiving ground separately,data transmission radio stations can transmit instructions to each other.The synchronous acquisition of downhole transmitting monitoring signal and receiving signal can be achieved by the radios combined with the synchronous clock.The test shows that the synchronization error between transmitting and receiving system is less than 100 ns.