利用D-D中子发生器进行补偿中子孔隙度测井的模拟研究

Monte Carlo Simulation on Compensated Neutron Porosity Logging with D-D Neutron Generator

利用蒙特卡罗方法模拟研究了D-D脉冲中子源和Am-Be中子源产生的中子与地层的作用过程。得到热中子计数随着源距增加而呈指数下降,源距小于20cm时D-D中子管的热中子相对计数高于Am-Be中子源;源距大于20cm时比Am-Be中子源低。在低孔隙度(小于20%)地层D-D中子管补偿中子孔隙度测井的热中子计数比值略大于Am-Be中子源;高孔隙度(大于20%)地层D-D中子管的热中子计数比值远远大于Am-Be中子源,对地层孔隙度灵敏度增加。与Am-Be中子源相比,D-D中子管补偿中子孔隙度测井的探测深度略为降低,地层孔隙度测量的灵敏度增加,因此利用D-D中子管可以进行补偿中子孔隙度测井。

The process of neutron interaction induced by D-D neutron tube and Am-Be source is simulated using Monte Carlo method. It is concluded that the thermal neutron count descend exponentially as the spacing increases. When the spacing is less than 20 cm, relative count of thermal neutron induced by D-D neutron tube is higher than that by Am-Be neutron source. However, the conclusion is opposite when the spacing is more than 20 cm. In low porosity （less than 20%） formation, the ratio of thermal neutron count in near and far spacing generated by D-D neutron tube is slightly larger than that generated by Am-Be neutron source; but in high porosity （more than 20%） formation, the ratio of thermal neutron count generated by D-D neutron tube is much larger than that generated by AmBe neutron source, so that it increases the sensitivity to formation porosity. Its reflection to porosity is more sensitive if the porosity is higher. In addi- tion, compared with Am-Be neutron source, depth of detection with D-D neutron tube is slightly decreased, and the sensitivity of measurement to the formation porosity increases. Therefore, the compensated neutron porosity logging by using D-D neutron tube is feasible.