Field test of an experimental pulsed nuclear magnetism tool

An experimental skid-type pulsed nuclear magnetic resonance logging tool (PNMT) has been evaluated in Shell’s Johnson City test well. The tool shows considerable promise for logging producible fluid, porosity and permeability. The skid-type design has excellent vertical resolution, eliminates doping the borehole mud with magnetite and is also unaffected by the salinity of the mud. The PNMT provides a continuous log of transverse relaxation time distributions that can be used to estimate pore size distributions and producible fluid volumes in sandstones. Good agreement has been found &th mercury capillary pressure and centrifuge measurements on 30 Johnson City core plugs. Values of total porosity from the PNMT agree with core data in the clean sandstone and carbonate lithologies present in the test well. In shales, PNMT porosity values were found to be less than core values, as the PNMT measurement is relatively insensitive to the clay bound water and small pores associated with these rocks. The attenuated response in shales was verified with fresh shale core placed directly against the PNMT skid. The PNMT was able to identify very thin permeable sands not resolved on any of the standard logging tools run at Johnson City over the years. This thin bed resolution was supported with the Fullbore Formation MicroImager (FMI*) tool and additionally confirmed with core. The ability to resolve thin permeable sands should be useful in evaluahg thinly laminated sand/shale sequences.