脉冲中子俘获测井脉冲时序设计

Pulsed Neutron Capture Logging Pulse Sequence Design

为降低井眼环境对脉冲中子俘获测井的影响,提高脉冲中子测井功能兼容性。基于蒙特卡罗方法,通过对比双脉冲时序与多脉冲时序条件下脉冲中子俘获测井响应特征,对脉冲中子俘获测井脉冲时序进行优化设计,为一体化核测井仪器研发及应用奠定基础。研究结果表明:双脉冲时序和多脉冲时序下时间谱均能准确地计算地层俘获截面,受井眼流体的影响较小;双脉冲时序下的测井响应具有更低的统计误差、更快的测速,并且更易实现;多脉冲时序更易获取非弹性伽马计数率;对于不同测井参数单独测量时推荐使用双脉冲时序进行脉冲中子俘获测量,对于不同测井参数同时测量的一体化核测井仪器推荐使用多脉冲时序。

In order to reduce the influence of borehole environment on pulsed neutron capture(PNC)logging and improve the functional compatibility of pulse neutron logging.Based on the MonteCarlo method,the PNC logging pulse sequence is optimized by comparing the response characteristics under the condition of the double pulse sequence and the multi pulse sequence,which lays the foundation for the development of the integrated nuclear logging tool.The results show that the time spectrum of the double pulse sequence and multi pulse sequence can accurately calculate the formation capture cross section and it is less affected by borehole fluid.The logging response with double pulse sequence has lower statistical error,faster speed measurement and easier realization.It is easier to obtain the inelastic gamma count rate with multi pulse sequence.Therefore,the double pulse sequence is recommended for PNC measurement when different logging parameters are measured separately,and multi pulse sequence is recommended for the integrated nuclear logging tool while the different logging parameters are measured simultaneously.