Abstract:

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.

Key words: NMR T2 spectra, capillary pressure curves, sandstone formations, log interpretation.