二氧化碳气驱稠油层脉冲中子含气量监测方法

A method of monitoring gas saturation in carbon dioxide injection heavy oil reservoirs by pulsed neutron logging technology

提出了一种利用非弹性伽马射线与俘获伽马射线组合定量表征快中子散射截面(σf)的方法,从而基于三探测器脉冲中子测井技术实现了注CO_(2)稠油储集层含气饱和度的评价,分析了评价效果的影响因素并利用模拟实例验证了方法的有效性。利用蒙特卡罗模拟方法结合岩石体积物理模型,研究了σf与CO_(2)饱和度的响应关系,并建立饱和度解释模型,分析了地层温度压力、稠油密度、井眼流体及储集层CH_(4)含量对CO_(2)饱和度评价效果的影响。研究表明,通过次生伽马信息组合对σf进行表征可以消除地层岩性的影响;井眼流体与储集层CH_(4)含量是影响CO_(2)饱和度定量监测的主要因素,地层温度压力和稠油密度的影响可以忽略。模拟实例进一步验证了使用该方法进行注CO_(2)稠油储集层含气饱和度评价的可行性。

A method is proposed to characterize the fast neutron scattering cross-section(σf)quantitatively by the combination of inelastic gamma rays and captured gamma rays,so as to realize the gas saturation evaluation of CO_(2)-injected heavy oil reservoirs based on the three-detector pulsed neutron logging technology.Factors influencing of the evaluation effect of this method are analyzed and the effectiveness of this method is verified by a simulation example.By using the Monte Carlo simulation method and the physical model of bulk-volume rock,the relationship betweenσf and CO_(2) saturation is studied,and the saturation interpretation model is established.The influences of formation temperature and pressure,heavy oil density,borehole fluid and reservoir methane content on the evaluation results of CO_(2) saturation are analyzed.The results show that the characterization ofσf by the combination of secondary gamma information can eliminate the influence of formation lithology,borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO_(2) saturation,and the effects of formation temperature and pressure and heavy oil density are negligible.The simulation example verified the feasibility of the method for evaluating the CO_(2) saturation of CO_(2)-injected heavy oil reservoirs.