渤海J油田储层核磁共振测井孔隙度影响因素分析及校正

渤海J油田沙河街组储层核磁共振（NMR）测井孔隙度和岩心NMR孔隙度均低于岩心氦孔隙度，这种现象影响了NMR测井的应用效果．通过开展岩心NMR实验，对该研究区仪器采集参数、井眼环境以及储层流体性质等因素进行分析，发现造成储层NMR测井孔隙度偏低的主要原因是高矿化度泥浆滤液侵入．基于饱和不同矿化度盐水对T₂谱的影响规律，确定了需要对T₂谱进行形态校正的矿化度下限值，并建立了对应不同矿化度的T₂谱形态校正模型及NMR孔隙度校正方法．应用结果表明，校正后的NMR测井孔隙度与岩心氦孔隙度的平均相对误差从13.56%下降至2.81%，有效提高了NMR测井孔隙度的精度．

Factors Affecting and Correction Methods for Porosity Measured by NMR Logging in the J Oilfield of Bohai Bay

The porosity of reservoir bed and core in the Shahejie formation of the J oilfield of Bohai bay measured by nuclear magnetic resonance (NMR) logging were found to be lower than those measured by the reference helium method, affecting the application of NMR logging. NMR experiments on the core samples were performed to study the contributions of potential affecting factors, including instrument acquisition parameters, wellbore environment and reservoir fluid properties. The main reason for the lower porosity measured by NMR logging was found to be the intrusion of high salinity mud filtrate. The effects of brines with different salinity on NMR T₂ spectrum were analyzed, and the results were used to determine the lower limit of salinity required for morphological correction of the NMR T₂ spectrum. In view of that the intrusion of high salinity mud filtrate could affect the NMR T₂ spectrum during actual logging, a model for morphological correction of the NMR T₂ spectrum and a method to correct the NMR porosity at different salinity were established. The experimental results demonstrated that the average relative error of the NMR porosity reduced from 13.56% to 2.81% after correction.