Nuclear Magnetic Resonance Data

Science operator: BP Exploration( Alaska), Inc.

Hole: Mt. Elbert-01

Location: Milne Point, North Slope (Alaska)

Latitude: 70° 27' 20.304" N

Longitude: 149° 24' 38.8434" W

Logging date: February, 2007

Total penetration: 914 m (from kelly bushing)

Permafrost depth: 595 m (from kelly bushing)

Casing depth: 595 m (24.4 cm)

Kelly bushing: 16.8 m above sea level. Depth reference for all logs.

Ground elevation: 6.5 m above sea level

Gas hydrate zones: 649.8-666.3 m (Unit C), 614.4-627.9 m (Unit D)

Lithologies: Clay, silty clay, sand, silty sand, and interbedded pebbles.

The measurement of nuclear magnetic resonance (NMR) made by Schlumberger's Combinable Magnetic Resonance Tool (CMR) tool is summarized here. The basic technology behind this tool is based on the measurement of the relaxation time of the magnetically induced precession of polarized protons.

The Combinable Magnetic Resonance tool 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 0.3 ms to 3 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 porosity calculated from the density log).

See www.slb.com/-/media/files/fe/product-sheet/cmr-plus-ps 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.

Processed Data

The processing of the Mt. Elbert CMR data was performed by Schlumberger.

The NMR data are presented in the following ASCII files:

1) Files named 'cmr.dat' contain the following 1-D NMR log data (both main repeat pass included):

BFV (%) : CMR bound fluid volume

CMFF (%): CMR free fluid volume (%): free fluid volume

CMRP_3MS (%): CMR 3 ms porosity

KSDR (mD): permeability from CMR (Schlumberger model)

KTIM (mD): permeability from CMR (Timur model)

TCMR (%): CMR total porosity

T2LM (ms): T2 Logarithmic mean

2) Files named ' cmr-t2dist.dat' contain the T2 distribution (spectra; both main repeat pass included):

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).

3) File named cmr-proc.dat. According to the original Mt Elbert processing notes compiled by Tim Collett,"the repeat pass appears to be the better run of the two CMR runs. The gas hydrate saturation calculation in this file more closely resembles the EPT and resistivity-calculated gas hydrate saturations thanb the CMR main log".

All logs depths are referred to the kelly bushing, which is 5.6 m above sea level.

Additional information about the drilling and logging operations can be found in the Geological Survey of Canada Bulletin 601 (https://doi.org/10.4095/291751).

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.