井下套管柱自身磁场分布与无源磁测距井眼防碰机制研究

Cluster well group and well-factory technology are important measures to cost decreasing and benefit increasing for offshore and land oil exploration. During the drilling process, wellbore anti-collision is one key to implement these technology with safe and high efficiency. Most active magnetic ranging wellbore anti-collision methods can only be used while adjacent wells have not been put into production or have been shut down. Passive magnetic ranging wellbore anti-collision methods can directly detect the downhole casing string’s magnetic filed by MWD and is not restricted by the restricted condition above. However, downhole casing string’s magnetic field distribution and wellbore anti-collision mechanism by passive magnetic ranging are still misunderstood. Therefore, the research method coupled with the theoretical modeling analysis and the ground experiment will be used to establish theoretical analysis models to downhole casing string’s magnetic field distribution due to geomagnetic field, residual magnetism and their combination action. The downhole casing’s magnetization parameters (magnetic conductivity, magnetic remanence intensity) will be extracted by experimental dada. Then, downhole casing string’s magnetic field distribution characteristics will be analyzed deeply. The detective sensitivity parameters to the magnetic field, due to geomagnetic field, residual magnetism and their combination action, will be identified respectively. Accordingly, their detective ranges will be anticipated. At last, the passive magnetic ranging method to downhole casing string and wellbore anti-collision mechanism will be established and discussed. The research achievements can enlarge the detective range and enhance the detective accuracy of passive magnetic ranging method, and provide theoretical and technical supports for wellbore anti-collision during the drilling process of dense cluster well group and well-factory.

丛式井组和“井工厂”技术是海上石油开发和陆上油田降本增效的重要手段，钻井过程中井眼防碰问题是安全高效实施这些技术的关键之一。有源磁测距井眼防碰仅能在邻井未投产或已停产时使用，无源磁测距防碰方法直接利用MWD探测邻井套管柱自身磁场，不受该使用条件限制，但是目前对井下套管柱自身磁场分布与无源磁测距井眼防碰机制认识不清。本项目采用理论建模分析与地面实验相结合研究方法，建立地磁场、剩磁及其共同作用下井下套管柱自身磁场分布理论分析模型，利用实验数据提取套管磁化参数（磁导率、剩磁强度），深入分析井下套管柱自身磁场分布特征，识别出地磁场、剩磁及其共同作用下井下套管柱自身磁场可探测敏感性参数，预测出井下套管柱自身磁场可探测范围，建立井下套管柱无源磁测距定位方法与井眼防碰机制。研究成果能够增大无源磁测距探测方法的探测范围、提高探测精度，为密集丛式井组和“井工厂”钻井过程中安全高效实施井眼防碰作业提供支持。

目前，丛式井和加密井越来越多，井眼间距越来越小，如何避免井眼碰撞已经成为很重要的钻井技术问题。国外已经研发出了多种磁测距防碰预警技术。其中，有源磁测距探测方法需要将信号发生或接收装置下入已完钻邻井中，受邻井生产状况影响，使用条件受到限制。无源磁测距方法依托邻井套管自身磁场，不受邻井生产状况限制。弄清套管柱周围磁场分布规律是无源磁测距方法的首要条件。国内对套管柱周围磁场分布规律认识水平有限，亟需开展与之相关各项研究工作。.本项目围绕套管单根周围剩磁分布规律、套管柱周围磁场分布规律、基于套管柱周围磁场分布特点的无源磁测量方法等问题开展研究工作。首先，基于全尺寸套管单根周围剩磁磁场的实测结果，建立了非均匀磁化的套管单根周围剩磁磁场分布模型、套管柱周围感应磁场分布模型、套管柱周围磁场分布模型，利用所建立模型对不同磁极组合方式下套管柱周围磁场分布特征进行了求解。其次，通过室外实验的方法，研究了套管柱周围不同磁场参数沿套管轴向、径向以及不同方位的变化规律，并与理论模型结果进行对比分析。最后，基于以上理论与实验分析结果，给出了基于套管柱自身磁场的磁测距方法，并通过模型实例分析与实际测量对测距方法进行了验证。.研究结果表明，单根套管周围剩磁磁场主要分布在两端部，影响范围大于套管周围感应磁化场；套管中部感应磁化场在各个方位上影响范围相同，套管柱接箍附近的感应磁化场影响范围更大；接箍处采用不同剩磁磁极组合方式时，套管柱周围磁场异常范围与分布规律也不同，同磁极连接方式比异性磁极连接方式剩磁磁场影响范围更大，可以增加无源磁测距的探测范围。基于套管柱周围磁异常的理论分析与实际测量规律，探讨了基于套管自身磁场的无源磁测距方法，并给出了相应的误差修正方法；模拟结果表明该方法可以很好地反演出套管的相对位置，为无源磁测距井眼防碰技术研发提供支持。