核磁共振测井黏土束缚水计算新方法

黏土束缚水是储层测井评价的重要内容之一。采用扩散双电层理论推导出黏土束缚水孔隙度（?_cw）与阳离子交换量之间的理论公式，通过岩心阳离子交换实验测定?_cw。依据核磁共振—阳离子交换联测实验，对比分析了传统3ms黏土束缚水T₂截止值测定?_cw的误差，明确了黏土束缚水T₂截止值与核磁共振不同截止值计算的?_cw之间的变化规律，建立了变黏土束缚水T₂截止值计算模型，从而实现核磁共振测井精细计算?_cw的方法并给出具体计算步骤。应用效果表明，相比传统3ms核磁共振测井计算的?_cw，所提新方法计算结果更合理，与岩心分析结论更匹配，是黏土束缚水评价的一种有效手段。

A new method for calculating clay bound water in NMR logging

Clay bound water is one of the important indicators of reservoir logging evaluation. The theoretical formula reflecting the relationship between the clay bound water porosity and the cation exchange capacity (CEC) of clay is derived in light of the diffuse double layer theory, and then the clay bound water porosity is determined through the core cation exchange experiment. Depending on nuclear magnetic resonance (NMR) and cation exchange experiments,this paper analyzes the error of determining clay bound water porosity by a traditional method of utilizing the T₂ cutoff of 3ms clay bound water and clarifies the variation rules between the clay bound water porosity calculated by T₂ cutoff and different NMR cutoff. A model is established for the calculation of clay bound water porosity with variable T₂ cutoff of clay bound water. Further, a new method for its calculation in NMR logging is developed, with the specific calculation steps given in the paper. The application results show that the method is more reasonable and more suitable for core analysis than the traditional 3ms NMR logging method,which is an effective means of clay bound water evaluation.