可控中子孔隙度测井仪器设计

Design of controllable neutron porosity logging tool

源距与屏蔽体厚度是直接影响可控中子孔隙度测井仪器测量准确性的重要参数。源距不仅影响测井仪器的测量误差,还影响测井仪器对地层孔隙度的灵敏度。屏蔽体厚度是保障测井响应完全反映地层的重要参数。从灵敏度、屏蔽率以及误差3个方面确定可控中子孔隙度测井仪器的源距与屏蔽体厚度。研究结果表明:近探测器源距越小,测井仪器灵敏度越高;近远探测器的间距对测量误差的影响随间距的增大,先减小再增大;当屏蔽率在70%以上且屏蔽率随厚度的变化较为缓慢时的屏蔽体厚度可作为屏蔽体最低厚度。

The spacing and shielding thickness are important parameters that directly affects the measurement accuracy of controllable neutron porosity logging tool.The spacing not only affects the measurement error of logging tools,but also affects the sensitivity of logging tools to formation porosity.The shielding thickness is to ensure that the logging response is completely contributed by the formation.In this paper,the spacing and shielding thickness of the controllable neutron porosity logging tool are determined from the three aspects of sensitivity,shielding rate and error.The research results show that the smaller the spacing of the near detector,the higher the sensitivity of the logging tool.The influence of the distance between near and far detectors on the measurement error first decreases and then increases with the increase of the distance.When the shielding rate is above 70%and the shielding rate changes slowly with the thickness,the shielding thickness can be used as the minimum thickness of the shielding.