脉冲中子氯能谱测井的蒙特卡罗模拟研究

氯能谱测井是评价地层含油饱和度的有效方法,在高矿化度地层应用效果明显。传统氯能谱测井是采用镅铍中子源,利用蒙特卡罗数值模拟方法开展采用脉冲中子源的氯能谱测井响应及其影响因素研究,验证脉冲中子氯能谱测井的可行性。研究结果表明,氯能谱与热中子计数比值随着含油饱和度的增加呈线性减小趋势,且孔隙度越大越有利于饱和度评价;岩性对测井响应影响很大,若地层岩性已知可以消除其影响;泥质含量的影响很小,泥质含量较小时可以忽略其影响;地层水矿化度是限制氯能谱测井应用的因素,地层水矿化度大于40000mg/L时效果明显,地层水矿化度越高越有利于含油饱和度的确定;井眼尺寸越大氯能谱与热中子计数的比值越小,越不利于含油饱和度的确定;当井眼中含有矿化水时会使氯能谱与热中子计数的比值增加,在测井解释时需要对井眼流体做必要的校正。通过研究,验证了采用脉冲中子源进行氯能谱测井的可行性。

Monte Carlo Simulation on Logging Response and Controlling Factors of Pulsed Neutron Chlorine Logging

Chlorine spectrum logging tool is effective to determine oil saturation in a cased well.It is comparable with C/O logging and thermal neutron lifetime logging tools,especially in the formation with high salinity.Traditional chlorine spectrum logging tool uses Am-Be neutron source.In this study,Monte Carlo numerical simulation was carried out on the response and controlling factors of chlorine spectrum logging with pulsed neutron source,to investigate the feasibility of pulsed neutron chlorine spectrum logging.It can be concluded that:the ratio of gamma count in chlorine spectrum range to thermal neutron count decreases linearly with the increase of oil saturation;the higher the porosity,the more beneficial to the determination of oil saturation;lithology has a great effect on logging response,which can be eliminated at known lithology;shale has a slight effect,which can be ignored at low shale content;formation salinity influences chlorine spectrum logging response;when formation salinity is higher than 4%,chlorine spectrum logging works well;and the greater the salinity,the more beneficial to the determination of oil saturation;the larger the borehole,the smaller the ratio of gamma count in chlorine spectrum range to thermal neutron count,the worse to the determination of oil saturation;and the ratio increases if borehole fluid contains saline water,and the effect of borehole fluid should be corrected in log interpretation.The study has proved chlorine spectrum logging based on pulsed-neutron source is feasible.