利用俘获伽马能谱确定饱和度的可行性及蒙特卡罗模拟研究

The feasibility of formation water saturation measurement by using capture gamma spectroscopy and monte carlo simulation

脉冲中子伽马能谱测井是利用多探测器获取非弹性散射伽马、热中子俘获伽马能谱及伽马时间谱,通过C/O和地层宏观吸收截面来确定饱和度,但俘获伽马能谱的信息没有得到很好利用.在地层水矿化度较高的情况下,由于俘获伽马能谱的Si,Ca和H的能窗内总的伽马计数与Fe能窗内的伽马计数比值与含氯量有关,因此由俘获伽马能谱确定含水饱和度是可行的.利用MCNP（蒙特卡罗方法）模拟研究了三能窗计数与Fe能窗计数比值与饱和度、岩性、孔隙度、泥质含量、井眼持水率、地层水矿化度以及井眼套管等条件下的关系,为在高矿化度地区利用俘获伽马能谱确定饱和度的可行性在理论上提供了支持.

Pulsed neutron gamma spectroscopy logging is a method that it can determine formation saturation by using C/O and formation macroscopic absorption cross-section,Σ,obtained according to the inelastic gamma ray spectrum and thermal neutron capture gamma ray spectrum and gamma ray time spectrum of several detectors,but the information of capture gamma ray spectrum is not well used.The ratio,of gamma ray count rate of energy windows from Si,Ca,and H to that of energy window from Fe in accordance with their capture spectroscopy,is in connection with the content of Cl element under the condition of larger salinity of formation water.And then,the method of determining water saturation by using capture gamma ray spectrum is feasible.The relations between the ratio of the count from three energy windows to Fe energy window and formation water saturation,lithology,porosity,shale content,water holdup,water salinity and casing have been studied by using the Monte Carlo method.Therefore,this paper provides theoretical support for the feasibility of formation water saturation determination by means of thermal neutron capture spectroscopy.