Pulsed-neutron well logs (PNLs) were acquired to monitor CO₂ storage associated with enhanced oil recovery. This work quantifies the precision of repeat PNLs using data from four wells and 15 repeat PNLs. Root-mean-square (RMS) precision for the repeat PNLs was less than 3%, indicating good agreement between the baseline and repeat PNLs. Evaluations of scaled relative difference (Scaled-D) showed variation in precision among individual wells and formations. Analysis of false-positive rates (FPRs) across the entire data set showed that a Scaled-D threshold in sandstone formations of approximately ±8% resulted in a 1% FPR. These Scaled-D precision thresholds were used to estimate the value of CO₂ saturation able to be confidently distinguished from baseline. The detection limit for CO₂ is lowest for high-porosity formations filled with saline water and is highest for low-porosity formations filled with fresh water. Thus, detection of vertical out-of-zone CO₂ migration using repeat PNLs is a function of instrument precision, petrophysical properties, and hydrology, all of which must be taken into account as part of the monitoring program. The results of this work provide insight into how PNLs may be included within monitoring plans to detect vertical out-of-zone CO₂ migration along a wellbore or instances of wellbore failure and provide a quantitative basis for establishing detection limits of repeat PNLs to distinguish change from baseline conditions.

采集了脉冲中子测井曲线（PNL）以监测与提高采油率相关的CO ₂储存。这项工作使用来自四个孔和15个重复PNL的数据来量化重复PNL的精度。重复PNL的均方根（RMS）精度小于3％，表明基线和重复PNL之间的一致性很好。比例相对差（Scaled-D）的评估显示了各个井和地层之间的精度差异。对整个数据集的假阳性率（FPR）的分析表明，砂岩岩层中的Scaled D阈值约为±8％，导致FPR为1％。这些Scaled D精度阈值用于估算能够与基准区分开来的CO ₂饱和度值。一氧化碳的检出限₂对于充满盐水的高孔隙度地层最低，而对于充满淡水的低孔隙度地层最高。因此，使用重复PNL检测垂直区域外CO ₂迁移是仪器精度，岩石物理特性和水文学的函数，所有这些都必须作为监视程序的一部分加以考虑。这项工作的结果提供了有关在监测计划中如何包括PNL的信息，以检测沿井眼或井眼故障实例的垂直区域外CO ₂迁移，并为建立重复PNL的检测极限以区分变化提供定量依据从基准条件。