测井技术2026，Vol.50Issue(3)：483-490,8.DOI:10.16489/j.issn.1004-1338.2026.03.010
套管结垢对脉冲中子-中子测井的影响及校正
Influence and Correction of Casing Wall Scale Deposits on Pulsed Neutron-Neutron Logging
摘要
Abstract
To address the issue that casing scale interferes with the calculation of formation macroscopic capture cross-section(Sigma)and reduces the accuracy of residual oil saturation evaluation in pulsed neutron-neutron(PNN)logging through cased holes,this paper establishes a three-dimensional numerical model of PNN instrument,wellbore and formation using the Monte Carlo simulation software.The simulation reproduces the slowing-down and capture processes of neutrons in the scaled borehole and formation.The effects of scale type,thickness,and composition on thermal neutron time spectra,neutron distribution,and measured Sigma are analyzed.A self-compensation correction method for the formation Sigma is developed and validated with field log data.The results show that:①Casing scale replaces borehole fluid,reducing the fast neutron slowing-down capability.Corrosion scale containing elements with high thermal neutron capture cross-section(e.g.,Cl)shortens the thermal neutron lifetime,leading to overestimation of the formation Sigma,whereas sedimentary scale weakens the thermal neutron capture capability,resulting in underestimation of Sigma.②The formation Sigma and the near-to-far detector thermal neutron count ratio increase linearly with the thickness of corrosion scale,while they decrease linearly with the thickness of sedimentary scale.The magnitude of this effect varies with formation porosity.For each 1 cm increase in corrosion scale thickness,formation Sigma increases by 3.37 c.u.in a formation with 8%porosity and by 3.69 c.u.in a formation with 15%porosity.③A higher NaCl content in the corrosion scale leads to a more pronounced influence on the formation Sigma.④The correction amount of the formation Sigma exhibits a linear relationship with the difference between the cased-hole neutron porosity and the compensated neutron porosity.The proposed self-compensation correction method achieves an average absolute error of only 0.29 c.u.after correction.It is concluded that casing scale significantly disturbs the logging response by altering neutron slowing-down and capture processes.The self-compensation correction method based on the thermal neutron count ratio and compensated neutron porosity effectively eliminates the scale effect,substantially improving the accuracy of formation Sigma calculation and the reliability of residual oil saturation evaluation,thus providing key technical support for dynamic monitoring of residual oil in cased holes.关键词
脉冲中子-中子测井/地层宏观俘获截面/套管结垢/数值模拟/自补偿校正/热中子时间谱/剩余油饱和度/中子孔隙度Key words
pulsed neutron-neutron(PNN)logging/formation macroscopic capture cross section/casing scale/simulation/self-compensation correction/thermal neutron time spectrum/residual oil saturation/neutron porosity分类
天文与地球科学引用本文复制引用
何晓君,李政,梁晓宇,张慧,雷刚,张锋..套管结垢对脉冲中子-中子测井的影响及校正[J].测井技术,2026,50(3):483-490,8.基金项目
国家自然科学基金项目"套管井X射线散射密度成像机理与探测方法研究"(42474155) （42474155）
国家自然科学基金项目"基于伽马-伽马反符合的随钻地层元素测井方法研究"(42174147) （42174147）
国家科技重大专项课题"万米深层复杂环境测井采集质控与数据处理"(2025ZD1402105) （2025ZD1402105）
国家科技重大专项课题"成像测井智能化处理解释系统"(2025ZD1401104) （2025ZD1401104）
