脉冲中子源密度测井进展

Pulsed neutron source density logging progress

密度是储层评价的重要参数.传统的密度测井是测量137Cs同位素放出的伽马射线与地层作用后的剩余伽马射线强度.虽然在密度测量方面已经非常成熟,但是由于同位素源具有放射性危害,使得脉冲中子源密度测井技术应运而生.脉冲中子密度测井使用电控脉冲中子源,中子源发射14MeV的快中子,通过非弹散射和俘获放出伽马射线,伽马射线在伽马源和探测器之间的地层中衰减,据此计算地层密度.脉冲中子密度测井可以计算密度、识别地层骨架,且探测深度大,没有放射性危害,因此越来越受到青睐,商用测井仪器已投入使用.另一方面,因为脉冲中子源密度测井与传统密度测井本质上有所区别,次生伽马源能量不单一、位置不固定,使得该方法的研究也面临着一些新的挑战,需要进一步深入的研究与测试.本文对脉冲中子源密度测井的方法原理、γ场特性、仪器的研究与应用以及未来发展方向进行介绍,以期对我国未来此类仪器的研发与解释方法研究提供一定的借鉴.

Formation density is one of the important parameters of formation evaluation. Traditional density logging is a measure of the residual strength of gamma rays which is emitted by 137 cs isotope, while in terms of density measurement has been very mature,but because of the traditional method of isotope source radioactive hazard,the pulse neutron source density logging technology arises at the historic moment.The method uses electric control source,electric once closed,the instrument will no longer work,so compared with the traditional density logging,greatly small radiation fears.Pulsed neutron source emission of 14 mev neutron,released gamma rays by inelastic scattering and capture,the gamma rays attenuated in the strata between the source and detector,on the basis of it calculating formation density. This method can divide gas formation skeleton,recognite formation skeleton,and almost not affected by formation shale content or the effect of natural gas in the pore,so more and more get the favour of various oil unit,commercial logging instrument has been put into use.On the other hand,pulsed neutron density logging and the traditional density logging essentially different,so the method of research also face some new challenges.Because of the pulsed neutron source density logging and the traditional density logging,essentially secondary gamma energy is not a single source,location is not fixed,makes the study of the method are also facing some new challenges,need further study and test.In this paper,the principle of pulsed neutron source density logging method,features,challenges and future direction will be introduced,providing a certain reference for our country on the developement of such instruments and interpretation methods.