Nuclear magnetic resonance pulse sequences for determining bound fluid volume

摘要

An NMR pulse sequence for use in a borehole logging tool includes a series of CPMG pulses according to:Tr - 90°±x - (tcp - 180°y - tcp - echoj) where j is the index of CPMG echoes gathered, Tr is wait time, tcp is the Carr-Purcell spacing. This pulse sequence is used to determine Bound Fluid Volume (BFV) which is subtracted from total porosity to yield Unbound Fluid Volume (UFV) of a formation surrounding the borehole. Measuring the BVF, the amount of rapidly relaxing fluid (less than 50 ms), is more efficient than measuring UFV (up to 2 secs), and is insensitive to motion of the logging tool.