核磁共振T_2谱法估算毛管压力曲线综述

DERIVING CAPILLARY PRESURE CURVES FROM NMR T_2 SPECTRA

用油藏实测NMR T2 谱换算毛管压力曲线 ,首先需正确确定T2 截止值 ,将T2 谱划分为束缚流体T2 谱和可动流体T2 谱 ,然后对可动流体T2 谱进行烃影响的校正 ,校正后的可动流体T2 谱加上束缚水T2 谱获得SW 为 1条件下的T2 谱 ,然后用换算系数κ将T2 谱直接转换成毛管压力曲线。经大量岩心分析和实际NMR测井数据试验表明 ,碎屑砂岩油藏NMR测井T2 分布数据估算毛管压力曲线方法可靠 ,与岩心压汞毛管压力曲线吻合 ,其精度相当于常规测井解释。应用这一方法换算的毛管压力曲线可用于确定含油 (气 )深度范围的饱和度—高度关系 ,确定油藏自由水面位置。

NMR T 2 distribution data obtained on reservoir real log are converted directly to capillary pressure curves. Firstly the T 2 cut-off values were determined, and the T 2 spectra were divided into irreducible water spectra and moveable water spectra. Then the moveable water spectra were corrected for hydrocarbon effects to reconstruct moveable water spectra, which were then added to the irreducible water spectra to obtain the T 2 spectra at S W=1. Using a converting coefficient κ, the T 2 spectra at S W=1 were able to be converted directly to capillary pressure curve. The key of the method is the correction of hydrocarbon effects on the moveable water spectra and the determination of the optimumκ.We have demonstrated that for sandstone formations capillary pressure curves can be reliably derived from NMR data with an accuracy that is equivalent to standard log interpretation. This was verified through an extensive core study as well as using real log data. This allows obtaining a reliable saturation-height function also in oil(or gas) bearing depth intervals.