碳氧比能谱测井基准问题的数值模拟

Numerical Simulation on a Benchmark Problem of C/O Logging

碳氧比能谱测井的数值模拟是涉及时间变量的中子-光子-电子联合输运的复杂问题。使用现有MCNP程序数值模拟碳氧比能谱测井遇到了2个主要困难:脉冲幅度谱的统计误差过大和F8计数不能分别得到非弹谱和俘获谱。将计算分2步进行:先用MCNP程序分别计算进入探测器的归一化中子激发γ流,以及各向同性γ流照射探测器端面时的响应函数矩阵;然后用自编程序计算两者的卷积,从而得到仪器的脉冲幅度谱。从简化基准问题的数值模拟结果看,该方法可以用于研究碳氧比能谱测井。

Numerical simulation of C/O spectral well logging is a complex problem involving in neutron-photon-electron coupling transportation with time dependence. There are two main difficulties in simulating C/O logging with available edition of MCNP code： the statistic error of the pulse height spectrum is too big, as well as the inelastic spectrum and the capture spectrum cannot be scored separately. Now the calculation is divided into two steps： first with MCNP code to separately calculate the neutron-induced gamma flux irradiating the detector, and the response function matrix of the detector whose bottom is irradiated by an isotropic gamma flux; then with a self-made program to calculate the convolution of the flux and the matrix to obtain the pulse height spectrum. Based on the simulation result of a simplified benchmark problem, the method can be used in the study of C/O spectral well logging.