PNN测井清污混注水淹层剩余油饱和度计算方法

The calculation method of residual oil saturation by PNN logging in water flooded interval injected by fresh water and sewage

过套管脉冲中子—中子(PNN)测井技术通过测量未被地层俘获的热中子数量来识别流体性质,解决了水淹层电性测井响应不明显以及中子寿命测井受伽马本底影响的问题。本文引入自适应遗传算法,通过选择、交叉、变异概率的设定以及在标准层中选取初始种群的方法,有效消除了多种非地质因素的影响,得到解释参数最优解;针对研究区块清污混注导致混合地层水矿化度变化大的特点,提出变参数PNN解释方法,分小层计算混合地层水宏观俘获截面,达到准确识别水淹层、大幅度提高剩余油饱和度计算精度的效果。

Pulsed neutron-neutron(PNN) logging technology through casing can identify fluid properties by measuring the number of thermal neutrons not captured by formation.It solves the problems of unclear response of electrical logging in watered-out zone and the influence of gamma background on neutron lifetime logging.In this paper, an adaptive genetic algorithm was utilized to eliminate the influence of non-geological factors and obtain the optimum solution of PNN interpretation parameters by setting the probability of selection, crossover and mutation and selecting the initial population in the standard layer.In view of the great change of salinity of mixed formation water due to interval injection by fresh water and sewage, the authors propose a variable parameter PNN interpretation method for calculating the macroscopic capture cross section of mixed formation water in small layers, so as to accurately identify the flooded layer and greatly improve the calculation accuracy of residual oil saturation.