热中子成像(TNIS)测井在低矿化度储层中适用性研究

Applicability Research of Thermal Neutron Imaging System(TNIS) Logging in Low Salinity Reservoir

华北油田冀中地区大部分油藏地层水矿化度低,储层物性差异大,给剩余油饱和度测井和解释评价带来困难。利用蒙特卡罗模拟方法模拟低矿化度、不同孔隙度、不同含油饱和度储层情况下,TNIS(Thermal Neutron Imaging System)近探测器记录的热中子时间谱。通过对不同模拟条件下热中子俘获截面、计数率截止时间差值分析研究认为,不同含油饱和度的计数率截止时间相对变化率均明显高于俘获截面相对变化率,TNIS测井利用热中子计数率成像可以辅助俘获成像在低矿化度、低孔隙度储层更好地分析油水关系。在低矿化度、低孔隙度储层,TNIS测井比PNN测井油水识别能力更强;采用改进的—Σ交会图法计算饱和度,通过分别确定经孔隙度校正后的纯水线和纯烃线,并对Σma进行泥质校正,运用内插法计算含水饱和度。该解释方法排除了泥质含量及孔隙度对测量值的影响,经过孔隙度校正扩大了孔隙流体的信息,提高了在低矿化度、非均质储层的饱和度计算精度。20井次的TNIS测井实例表明,TNIS测井适用于低矿化度储层的剩余油饱和度评价,在识别完井遗漏的潜力层、低电阻率油层、水淹层方面取得了良好效果。采油厂根据资料进行卡层、补孔作业见到明显的增油效果。

In Jizhong oilfield,The water salinity of most reservoirs is lower,the physical properties of reservoirs are very different.It is difficult to remaining oil saturation logging and interpretation.We use the Monte Carlo simulation to simulate the thermal neutron time spectrum recorded by TNIS(Thermal Neutron Imaging System)near detector on low salinity,different porosity and oil saturation conditions.By analyzing difference value ofΣ and cut-off time on different simulation conditions,it suggests that the relative rate of cut-off time on different oil saturation is significantly higher than that of Σ.So,based on thermal neutron counting rate imaging aiding thermal neutron capture imaging,TNIS logging can identify oil-water relationship in the low salinity and low porosity reservoirs.In the low salinity and low porosity reservoirs,the oil-water identification ability of TNIS logging is better than that of PNN logging;Using the improved —Σ crossplot to calculate the saturation,interpolation method is used to calculate water saturation by determining 100% water saturated line and 100% hydrocarbon saturated line standardized for porosity andΣmacorrected for shaliness.The method can eliminate the influenceof shale content and porosity on the measured values,the influence of pore fluid can be enlarged after porosity correction,the accuracy of saturation calculation can be improved in low salinity and heterogeneous reservoirs;20TNIS logging examples show that TNIS logging is suitable for remaining oil saturation evaluation in low salinity reservoirs,the missing potential reservoirs,low resistance oil reservoirs and water flooded reservoirs have been identified.According to TNIS interpretation results,obvious economic benefits have been brought to the oil production plants by sealing and supplementary perforating operations for reservoirs.