随钻核磁共振测井探测器构建方法研究  

Construction method study of NMR probe for logging while drilling

作　　者：李新[1,2] 罗嗣慧 肖立志[2] 孙哲[2] 汪正垛 LI Xin;LUO Sihui;XIAO Lizhi;SUN Zhe;WANG Zhengduo(State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development,Sinopec Research Institute of Petroleum Engineering,Beijing 100101,China;State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum-Beijing,Beijing 102249,China)

机构地区：[1]中国石化石油工程技术研究院页岩油气富集机理与有效开发国家重点实验室,北京100101 [2]中国石油大学(北京)油气资源与探测国家重点实验室,北京102249

出　　处：《石油科学通报》2020年第2期172-181,共10页Petroleum Science Bulletin

基　　金：国家重大科研仪器研制项目“极端环境核磁共振科学仪器研制”(21427812);国家科技重大专项“低渗透储层高精度随钻成像技术研究”(2016ZX05021-002)资助。

摘　　要：随钻核磁共振测井技术在钻井过程中实时获得油气藏的地球物理信息,钻井条件下的恶劣环境对随钻核磁共振测井探测器的设计和实现提出挑战。本文探讨了随钻核磁共振探测器设计的基础工程和科学问题,基于井下条件和核磁共振测量的特殊性研究探测器构建方法。采用居中式测量、旋转对称低梯度静磁场、单一工作频率、适中探测深度、中等敏感区高度等构建适于标准钻铤的探测器实用结构。主磁体基于经典“inside-out”组合,引入聚焦磁体改善敏感区形状,利用2D和3D有限元方法仿真模拟电磁场分布,研究得到共振频率、静磁场梯度和敏感区等探测特性。磁体组合产生的静磁场旋转对称、梯度中等,有利于降低仪器轴向和径向对测量的影响。收发线圈由多匝铜带绕螺线管构成,产生轴对称的射频场,推导调谐和匹配计算方法得到谐振快速调节图版,将样机天线阻抗调谐与谱仪系统匹配提高发射效率。在实验室搭建了全尺寸随钻核磁共振测井探测器,利用自研电路系统联调验证方案。开展了多等待时间和多回波间隔的回波串采集实验,利用正则化拉普拉斯逆变换得到单相流体样品的横向弛豫时间分布。实验结果表明,核磁共振回波串信号信噪比良好,横向弛豫时间分布呈单峰分布并与期望值一致,验证了探测器构建方法和方案设计。The nuclear magnetic resonance logging while drilling(NMR LWD)technique has advantages of providing real-time petrophysical information of in-situ oil&gas reservoirs during drilling.However,rigorous and harsh downhole conditions during NMR measurement pose great challenges for NMR LWD sensor design and implementation,including restricted space,motion states and limited downhole power supply.In this paper,fundamental engineering and scientific issues of NMR-LWD sensors are discussed based on special drilling downhole conditions and special features of NMR measurements.Key suggestions for NMR LWD sensor design are proposed.These are mandrel centered-type measurement,axis-symmetric low gradient fields,single frequency,moderate depth of investigation(DOI)and region of interest(ROI)height,a simple and practical assembly structure suitable for drill collars.A novel NMR LWD probe design is proposed based on the above understanding,where DOI and ROI are developed by using an optimized magnet configuration and permanent magnetic materials.The main magnet assembly is based on a classical inside-out configuration with a size constraint of a standard 6.75 inch non-magnetic drill collar,which is then improved by utilizing a circular focusing magnet between them.Static magnetic field distributions of the designed NMR sensor are given with 2D and 3D FEM methods.Characteristics were investigated including Larmor frequencies,static magnetic field gradient and sensitive volumes.The static magnetic field B0z produced by this magnet assembly is rotationally symmetrical with high resonant frequency,signal intensity and a compromised magnetic gradient,which has the advantage of alleviating axial and radial movement effects on measurement.The TR coil is a solenoid made of several turns of copper belts,resulting in an axisymmetric RF B1 field,which has a natural perpendicular relationship with B0z.Tuning and matching procedures are also discussed and calculated,several reference charts of capacities combination are given for rapid reson

关 键 词：随钻核磁共振 聚焦磁体 探测器 梯度磁场 

分 类 号：P631.81[天文地球—地质矿产勘探]