基于微扰理论的伽马-伽马密度测井快速正演方法

伽马-伽马密度快速正演结果作为中子和密度联合反演模型的输入,对实时反演确定地层几何结构及属性参数具有重要的意义.基于时间独立的玻耳兹曼输运方程,结合微扰理论与蒙特卡罗(Monte Carlo N Particle Transport Code,MCNP)模拟,形成了伽马-伽马密度快速计算方法.以双源距补偿密度仪器参数为基准,建立了不同基准密度地层条件下的扰动灵敏度函数数据库.分析对比了快速计算和蒙特卡罗模拟在不同岩性密度、水平层状地层及倾斜地层条件下的密度结果与误差.结果表明: 不同地层条件下的伽马-伽马密度快速计算结果与MCNP模拟结果吻合,三种岩性(砂岩、碳酸岩和白云岩)密度计算的平均误差小于0.01 g·cm^-3且与MCNP模拟速度相比,快速计算效率提高10⁶倍.

A fast forward method of gamma-gamma density logging based on perturbation theory

The fast forward modeling result of gamma-gamma density is used as the input of the neutron and density joint inversion model,which is of great significance for real-time inversion to determine the formation geometry and attribute parameters. Based on the time-independent Boltzmann transport equation,combined with the perturbation theory and Monte Carlo simulation,a fast calculation method of gamma-gamma density is proposed. The compensation density logging is adopted to establish the database of the perturbation sensitivity function under different reference formation conditions. The density responses and errors of fast calculation and MCNP simulation under different lithological densities,horizontally layered formations and inclined formations are analyzed and compared. The results show that the fast calculation results of gamma-gamma density logging under different formation conditions are consistent with the MCNP simulations. The average error of the three lithological (sandstone,carbonatite and dolomite) density calculations is less than 0.01 g·cm-3 and compared with the MCNP simulation speed,the fast calculation efficiency is increased by 106 times.