原油的核磁共振弛豫特性

地下原油的成分复杂，粘度变化范围很大，具有很宽的核磁共振（NMR）弛豫分布特性。研究原油的NMR弛豫特性随原油粘度、NMR仪器测量频率以及测量回波间隔(TE)等的不同而发生的变化，对利用NMR测井资料准确识别和评价油水层具有重要的指导意义。利用两种工作频率（2MHz和23MHz）的NMR谱分析仪器测量了不同粘度原油样品的NMR弛豫时间。结果表明：轻质油的纵向弛豫时间（T₁）和横向弛豫时间（T₂）近似相等，且在双对数坐标系下与原油粘度、粘度/温度的比值成反比关系；稠油的T₁大于T₂，其T₁/T₂比值随测量频率、粘度/温度比值的增加而增大；仪器测量频率对轻质油弛豫影响很小，而对稠油的弛豫影响较大；随测量回波间隔的增加，稠油的视横向弛豫时间增大，且幅度减小。

NMR RELAXATION PROPERTIES OF CRUDE OILS

The crude oil is of broad distributions of NMR relaxation for their complex components and changeable viscosity. It is important for interpretation of NMR logging to distinguish the oil and water formations to study on the crude oil NMR relaxation properties changing with different viscosity, work ing frequency and echo spacing TE. The dead oil NMR relaxation times are measured with two working frequency (2 Hz and 23MHz) NMR spectrometers in this paper. The results show that, light oil has similar T₁and T₂, and inversely proportional to viscosity, viscosity/temperature in logarithmic coordinates. However, heavy oil has greater T₁ than T₂,T₁/ T₂ is increasing as the increases of working frequency and viscosity/temperature. The relaxation time of light oil is not sensitive to the working frequency of the NMR spectrometer. Heavy oil relaxation time is related with working frequency. For heavy crude oil, apparent T2 relaxation time increases and the signal amplitude decreases as increasing echo spacing TE