薄互层页岩油核磁共振测井响应特征——以准噶尔盆地二叠系风城组为例

为明确核磁共振(nuclear magnetic resonance, NMR)测井仪纵向分辨率对薄互层陆相页岩响应特征的影响，以准噶尔盆地二叠系风城组3组薄互层接触面全直径岩心为研究对象，通过设计不同岩心取样方式，模拟核磁共振仪器不同纵向分辨对薄互层的核磁共振测量。研究核磁共振仪器纵向分辨率在不同薄互层厚度情况下横向弛豫时间T₂谱的响应特征的差异，明确核磁共振仪器纵向分辨率对T₂谱形态、核磁孔隙度、核磁T₂特征截止值及几何平均值的影响。结果表明：当薄互层物性差别较大且仪器纵向分辨率较低时，T₂谱形态不能准确反映真实储层特征，进行核磁测井资料解释需要考虑分辨率的影响；核磁孔隙度受仪器纵向分辨率影响较小，是薄互层探测区域的线性平均值；T₂特征截止值和几何均值会受到较大影响，会造成核磁有效孔隙度、可动流体饱和度和核磁渗透率偏小。研究结果对薄互层型页岩储层核磁共振测井评价具有重要指导意义，为核磁共振测井在页岩薄互层储层性质评价提供了参考依据。

NMR Logging Response Characteristics of Thin Interbedded Shale Oil - an Example from the Permian Fengcheng Formation in the Junggar Basin

The effect of longitudinal resolution of nuclear magnetic resonance (NMR) logging tool was investigated on response characteristics of thin interbedded continental shale. The full-diameter cores of three sets of thin interlayer contacts of the Permian Fengcheng Formation in the Junggar Basin were used to study the NMR measurements of the thin interlayer by designing different core sampling methods and simulating different longitudinal resolutions of the NMR instrument. The differences in the response characteristics of the T2 spectrum when the longitudinal resolution of the NMR instrument and the thickness of the thin interlayer are investigated. The effects of the longitudinal resolution of the NMR instrument on the shape of the T2 spectrum, the total porosity of the NMR, the cutoff value of the NMR T2 and the geometric mean were clarified. Studies have shown that when the physical properties of the thin interbeds are quite different and the longitudinal resolution of the instrument is low, the T2 spectral shape cannot accurately reflect the real reservoir characteristics. The interpretation of NMR log data needs to be carried out taking into account the effect of resolution. The NMR porosity is less affected by the longitudinal resolution of the instrument and is a linear average of the detection area of thin interlayers. The T2 cut-off value and geometric mean will be greatly affected, which will cause the NMR effective porosity, movable fluid saturation and NMR permeability to be small. The research results have important guiding significance for NMR logging evaluation of thin interbedded shale reservoirs, and provide a reference for NMR logging to evaluate the properties of thin interbedded shale reservoirs..