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过钻杆存储测井是评价水平井、大斜度井地层参数的一种重要的测井方式.本文针对过钻杆中子孔隙度测井中源和探测器相对钻杆的位置开展研究,并与电缆、随钻中子孔隙度测井响应进行了对比.利用蒙特卡罗方法建立了过钻杆、电缆及随钻中子孔隙度三种仪器模型,模拟研究了热中子分布及近、远探测器计数比值与孔隙度的响应关系,分析了孔隙度测量精度和相对灵敏度以及井眼尺寸的影响.结果表明:源在钻杆内探测器在钻杆外的测量方式近探测器计数率和孔隙度测量精度高;且低孔隙度时相对灵敏度高,同时防止测量过程中放射源的脱落.随着孔隙度增大,随钻仪器近探测器计数率增加,而电缆与过钻杆仪器计数率降低;随着井眼尺寸增加,近、远热中子计数率比值率增大,过钻杆和电缆近探测器计数率降低,随钻近探测器计数率增加.源在钻杆内探测器在钻杆外的测量方式在保证孔隙度测量精度及灵敏度的同时,提高了放射性源测井的安全性.
Drill pipe storage logging is an important logging method to evaluate the formation parameters of horizontal well and high-deviated well.Based on the study of the relative position of the source and the detector relative to the drill pipe in the over-boring neutron porosity well logging, And compared with the cable, while drilling neutron porosity logging response.Using Monte Carlo method to establish three instrument models of over-drill pipe, cable and the neutron porosity of drilling while simulating the thermal neutron distribution and near , The relationship between the detector ratio and the porosity, and the influence of porosity measurement accuracy and relative sensitivity and wellbore size were analyzed.The results show that the measurement of source outside the drill pipe outside the drill pipe is close to the detector count High accuracy of porosity and porosity, high relative sensitivity at low porosity, and prevention of radioactive sources from falling off during measurement. As the porosity increases, the count rate of detectors near the drilling tool increases, With the increase of borehole size, the ratio of count rates of near-neutron and neutron neutrons increases, the count rate of over-drill and cable near detectors decreases, and the count rate increases near the detector while drilling. Internal detector in the drill pipe The porosity measurement ensure accuracy and sensitivity of measurement, while improving the security of radioactive sources logging.