广域-伪随机信号电磁法井间油气储层识别

The domestic oil recovery is only about 30%. A large amount of remaining oil is distributed in crosswell. For the improvement of oil recovery and mineable reserves, it is important to research the identification technology of oil and gas reservoir in crosswell. Based on wide field - pseudo random signal electromagnetic method, this project makes one casing of the well group as emission electric dipole, and makes the other casings as receiving electric dipoles. When pseudo-random multi-frequency signal is applied to the transmission source, the apparent resistivity of detection area can be extracted according to received responses. Which is achieved by iterative calculation. The production casings have the characteristics of good electrical connectivity and high conductivity. Coupled with the casing length is the same as production well depth, it is easy to build high-power transmitter. Which can achieve long-range detection of inter-well reservoir. Pseudo-random multi-frequency signal containing a plurality of main frequency, and having the reasonable frequency distribution. It can obtain a plurality of subsurface resistivity by once launch. Which significantly improve the measuring speed and efficiency of electromagnetic exploration method. This item researches construction and parameter optimization method for long distance electrical dipole. And the electromagnetic response characteristics of different resistivity or depths reservoir is also analyzed. Combined with response signal detection and experiment verification, it can obtain the recognition theory and method about crosswell reservoir with wide field-pseudo random signal electromagnetic method.

我国原油采收率仅为30%左右，井间是剩余石油分布的主要区域，开展井间油气储层识别对于提高采收率和增加可采储量具有重要意义。本项目基于广域-伪随机信号电磁法，将油气井网中一口生产井的套管作为发射电偶源，并对其施加伪随机多频信号，利用其余生产井套管构建接收电偶极子，工作时一次发射同时接收。根据接收井中的电磁场响应，迭代计算提取探测区域视电阻率，确定井间油气储层的分布状况。套管电连通性好、电导率高，长度与井深基本相同，因而有利于构建大功率发射电偶源，实现井间储层的远距离探测。伪随机多频信号含有多个主频率、频率分布合理，一次发射就能获得多个深度的地下电阻率信息，可以显著提高电磁法的测量速度与勘探效率。项目通过研究长距离电偶极子构建与参数优化方法，分析不同深度与电阻率储层的电磁响应特征，结合相关响应信号检测与处理，并开展必要的实验验证，形成一种基于广域-伪随机信号电磁法的井间油气储层识别理论和方法。

本项目采用广域电磁法，以多频伪随机信号作为激励，将生产井网中的套管作为发射电偶源和接收电偶极子，实现井间剩余油分布的探测。构建了以生产井套管作为发射线源和接收电偶极子的工作装置，形成了基于伪随机电磁法的井间油气储层特征识别理论与方法，完成了井间电磁探测装置以及发射信号的参数优化。.项目主要研究内容包括：（1）详细分析电磁波在各媒质交界面处产生的传播效应，推导了多层介质的视电导率计算公式。采用电磁波传播理论计算了四层地电断面的视电导率曲线。（2）以27伪随机序列作为激励信号，分析了均匀地层中不同异常体情况下的电磁场分布状况。（3）提出采用离散循环相关辨识提取大地脉冲响应的方法，能够有效提高相关辨识精度。研究了不同参数条件下，m序列对于直流干扰、舒曼频率噪声以及正弦波噪声的抑制能力。（4）提出利用油气生产井的金属套管构建长偶极发射线源，并对其施加伪随机多频信号进行井间油气储层特征识别的方法。采用数字相干检测方法分别提取了不同井间距测线位置上，伪随机电磁响应各频率分量的幅度特征。.研究结果表明：（1）相比于几何因子理论的结果，采用电磁波传播理论计算得到视电导率，与原状地层的均方根误差降低了12%～45%。（2）采用27伪随机序列作为激励信号，不同时段的伪随机电磁响应，对于低阻体和高阻体均能达到良好的识别效果。（3）离散循环相关辨识提取大地脉冲响应的方法，能够有效提高相关辨识精度。m序列对于直流干扰、舒曼频率噪声以及正弦波噪声的具有较强抑制能力。（4）利用油气生产井的金属套管构建长偶极发射线源，并对其施加伪随机多频信号,通过提取不同井间距测线上伪随机电磁响应各频率分量的幅度特征，能够显著提高电法勘探的工作效率与探测精度。.通过研究，全面完成了任务书的各项研究内容。发表论文5篇，其中SCI检索2篇，EI检索1篇；申报发明专利4项，其中授权2项；登记计算机软件著作权4项，出版专著1部，培养研究生6人。