【摘要】 针对油基泥浆（Oil-Based Mud,OBM）的侵入而导致核磁共振（Nuclear Magnetic Resonance,NMR）测井中地层原油与滤液信号混叠、残余油饱和度评价困难的问题，以北部湾盆地涠西南凹陷低孔隙度低渗透率（简称低孔低渗）砂岩储层为研究对象，开展了在线驱替核磁共振实验，系统揭示了OBM滤液侵入后NMR的T₂谱变化规律，并提出了一套融合信号分解与构建水谱的残余油饱和度定量评价方法。实验选取12块覆盖不同物性特征的柱塞岩心（孔隙度3.17%～21.15%，渗透率0.01～29.50 mD*，孔隙度与渗透率的相关性R²=0.713 1）。结果表明，OBM滤液侵入后，岩心NMR的T₂谱呈现以100 ms为界的统一变化规律：短弛豫组分（T₂<100 ms）信号幅度减弱，长弛豫组分（T₂>100 ms）信号幅度增强。明确了流体信号分布模式：地层水与原油信号主要集中于短弛豫段，OBM滤液信号主要分布于长弛豫段，形成地层流体谱峰靠左、滤液谱峰靠右的特征。基于此，提出融合T₂谱组分分解与构建水谱的评价技术：首先采用非对称高斯函数与连续小波变换对混叠T₂谱进行高精度分解，分离地层原油与泥浆滤液信号；然后利用构建水谱差谱技术剔除滤液贡献，定量计算残余油孔隙度与饱和度。将该方法应用于北部湾盆地B井严重侵入层段，有效识别出长弛豫信号主要源自OBM滤液，计算的残余油饱和度均低于10%，与电缆地层测试数据及试油结论高度吻合。结论认为，该方法克服了OBM侵入下NMR测井流体信号混叠的技术难题，为油基泥浆钻井环境中低孔低渗储层残余油饱和度精细评价提供了可靠手段，具有较强的实用价值。更多还原

【Abstract】 To address the signal overlap between formation crude oil and oil-based mud（OBM） filtrate in nuclear magnetic resonance（NMR） logging T₂ spectra and the consequent challenge in accurately evaluating residual oil saturation, this study focuses on low-porosity and low-permeability sandstone reservoirs in the Weixi’nan sag, Beibuwan basin. Online displacement NMR experiments are systematically designed and conducted to reveal the evolution of NMR T₂ spectra after OBM filtrate invasion. Subsequently, a quantitative evaluation method for residual oil saturation integrating signal decomposition and constructed water spectrum is proposed. Experiments on 12 core plugs with diverse properties（porosity: 3.17%～21.15%, permeability: 0.01～29.5 mD, R²=0.713 1） reveal a consistent pattern: after OBM filtrate invasion, short relaxation components（T₂<100 ms） decrease, while long relaxation components（T₂>100 ms） increase. This establishes a characteristic distribution where formation water and crude oil signals concentrate in the short relaxation segment, and OBM filtrate signals dominate the long relaxation segment. Based on these findings, a combined approach is developed. First, asymmetric Gaussian functions and continuous wavelet transform enable high-precision decomposition of overlapping T₂ spectra to separate crude oil and filtrate signals. Second, the constructed water spectrum difference technique eliminates filtrate contribution, allowing quantitative calculation of residual oil porosity and saturation. Application to severely invaded intervals in well B, Beibuwan basin, successfully identifies long relaxation signals as primarily OBM filtrate. Calculated residual oil saturations are below 10%, closely matching wireline formation test data and production test conclusions. This method effectively overcomes fluid signal overlap challenges in NMR logging under OBM invasion, providing a reliable technique for fine evaluation of residual oil saturation in low-porosity and low-permeability reservoirs drilled with oil-based mud.更多还原