核磁共振T2谱法估算毛管压力曲线综述

用油藏实测NMRT2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。

DERIVING CAPILLARY PRESURE CURVES FROM NMR T2SPECTRA

NMR T2 distribution data obtained on reservoir real log are converted directly to capillary pressure curves. Firstly the T2 cut-off values were determined, and theT2spectra 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 T2 spectra at SW=1. Using a converting coefficient κ, theT2 spectra atSW=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 optimum κ. 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.