瞬变电磁井间涡流激发响应的实验研究

瞬变电磁井间涡流激发的二次场响应可以用于井间剩余油的检测,为提高剩余油采收率,提出基于全空间几何因子的井间勘探方法。利用铝板与全空间放置的发射和接收线圈进行瞬变电磁井间勘探实验,首先将有铝板存在和无铝板存在时接收线圈测量的瞬变电磁总响应相减去掉直接耦合信号,得到只与空间导电介质有关的涡流激发响应(该响应即为井间勘探的有用信号,与地层电导率成正比,可以用来反演地层电导率),然后用涡流激发响应的极性间接地对全空间几何因子极性特征进行定性实验验证,即全空间几何因子在发射或接收线圈两侧极性相反。利用全空间几何因子理论以及井间涡流激发响应解析解进行正演模拟,并与空气以及地层中实测得到的涡流激发响应波形进行对比,从而定量地验证了全空间几何因子在计算井间涡流激发响应时的可行性。通过改变发射与接收线圈的源距,发现了瞬变电磁全波响应以及与铝板有关的井间涡流激发响应幅度随源距的增大而逐渐变小的客观规律,即源距改变,接收线圈对涡流激发响应的灵敏度随之改变。

The secondary field response induced by eddy currents in transient electromagnetic soundings in wells can be used to identify the remaining oil in the interwell space.To improve the recovery of remaining oil,an interwell exploration method based on the full space geometry factor is proposed.The experiment was carried using an aluminum plate with the transmitting and receiving coils placed in the full space.Firstly,to remove the direct coupling signal,the total transient electromagnetic response measured by the receiving coil in the absence of the aluminum plate was subtracted from the response evaluated in the presence of the plate.Then,the eddy current excitation response associated with the conductive medium was obtained.This response contains a useful signal which can be used to invert the formation conductivity because the response is in fact proportional to the formation conductivity.Subsequently,the polarity of the eddy current excitation response is used to qualitatively verify the polarity characteristics of the full-space geometry.It was found that the full-space geometry factor presents opposite polarities on the transmitting and receiving coils.The full-space geometric factor theory and the analytic solution of the interwell eddy current excitation response are used in forward modeling to obtain the field response.Next,the waveforms of the response obtained were compared with those of the measured eddy current excitation response in the air and the stratum,thereby quantitatively verifying the feasibility of using the full-space geometric factor in calculating the interwell eddy current excitation response.By changing the source distance between the transmitting and receiving coils,we found that the transient electromagnetic full-wave response and the amplitude of the interwell eddy current excitation response associated with the aluminum plate both decreased as the distance increased.In other words,the sensitivity of the receiving coil to the eddy current excitation response changed with the distance to the source.

国家重点研发计划(2016YFC0802008)资助。