IODP Expedition 372 Nuclear Magnetic Resonance Data Processing
Magnetic Resonance Measurement
The proVISION tool used during Expedition 372 measures the nuclear magnetic resonance properties of hydrogen in the formation. Initially, the hydrogen atoms are aligned in the direction of a static magnetic field (B0). The hydrogen atoms are then tipped by a short burst from an oscillating magnetic field that is designed so that they precess in resonance in a plane perpendicular to B0. The precession of the hydrogen atoms induces a signal in the tool antenna, and the decay of this signal is measured as the transverse relaxation time, T2. Because the formation contains hydrogen in different forms (in water in large pores, small pores, and bound in clay minerals, and in methane hydrate), there is a distribution of T2 times, here given from 1 ms to 5 s. The T2 distribution is the basic output of NMR measurement. It is further processed to give the total pore volume (the total porosity) and pore volumes within different ranges of T2, such as the bound and free fluid volumes. The presence of gas hydrate is indicated by the deviation of the magnetic resonance porosity log from other porosity logs (such as density porosity).
See https://www.slb.com/-/media/files/drilling/brochure/provision-plus-lwd-br.ashx and https://ux.uis.no/~s-skj/NMR/Schlumberger/O0_CMR_OilRev.pdf for a more detailed description of the tool and its applications.
Additional information:
Collett, T.S., 2001, Review of well-log analysis techniques used to assess gas-hydrate-bearing reservoirs: In Natural Gas Hydrates: Occurrence, Distribution, and Detection, American Geophysical Union, Geophysical Monograph 124, p. 189-210.
Horkowitz, J., Crary, S., Ganesan, K., Heidler, R., Luong, B., Morley, J., Petricola, M., Prusiecki, C., Speier, P., Poitzsch, M., Scheibal, J.R., and Hashem, M., 2002, Applications of a new magnetic resonance logging-while-drilling tool in a Gulf of Mexico deepwater development well: Proceedings of the Society of Professional Well Log Analyst Annual Logging Symposium, June 2-5, 2002, Paper EEE, 14p.
Data Quality
Like for other other tools, the caliper measurement can provide a good indication of the NMR data quality, as this is affected when the distance between the tool sensor and the borehole wall is greater than 1 inch. In Expedition 372, the caliper log acquired by the NeoScope tool shows where the hole was enlarged and the CMR tool sensor may been more than 1 inch from the borehole wall.
Processed Data
The processing was performed by Schlumberger. The NMR data are presented in two ASCII files:
1) Files named 'nmr.dat' contain the following 1-D NMR log data:
BFV (%): bound fluid volume
KTIM (mD): Permeability from ProVISION (Timur model)
MRP (%): magnetic resonance porosity
T2LM (ms): T2 Logarithmic mean
2) Files named ' t2dist.dat' contain the T2 distribution (spectra):
T2 (%): at each depth, values of % volume are given for 30 relaxation times (T2) ranging from 3 to 3000 msec. The scale is logarithmic, and T2 is given both in msec and as the log10 of the time in msec, from 0 to 29 (because this is a whole number, = 10 * log10(T2/3) ≠ 0.5).
Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition report, Proceedings of the International Ocean Discovery Program, Expedition 372. For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.
After the moratorium period you may direct your questions to:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu