Irreducible fluid saturation determined by pulsed field gradient NMR

A new laboratory procedure, using a pulsed field gradient (PFG) NMR technique, for measuring the relative volumes of movable and nonmovable fluid in cores is reported. The saturations determined are in qualitative agreement with values obtained from mercury porosimetry and centrifuged gravimetric saturation measurements. An advantage of the PFG NMR method is that it is fast and does not require exchange of fluids, i.e., progressive desaturation. This may be important if wettability changes are a concern or for measurements on unconsolidated cores. The bound volume index, BVI, of some core plugs was additionally determined by CPMG NMR which was recently established as a down-hole measurement with the new generation of NMR well logging tools. Since PFG NMR is not sensitive to surface relaxivity, this technique can be used as a quick and independent check on the BVI values obtained by CPMG NMR.