Standard LWD Data Processing
Science operator: Texas A&M University
Hole: U1520A
Expedition: 372
Location: Hikurangi Subduction Margin (SW Pacific Ocean)
Latitude: 38° 68.1640' S
Longitude: 179° 7.9350' E
Logging date: December 27, 2017
Sea floor depth (driller's): 3538.3 m DRF
Sea floor depth (logger's): 3532.2 DSF
Total penetration: 104 m DSF
Total core recovered:
Oldest sediment recovered:
Lithology:
Data
The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in December 2017.
The logging of Hole U1520A was started on December 27 of 2017, reaching the total depth of 104 m DSF. The logging-while-drilling (LWD) tool string was assembled and contained NeoScope, geoVISION, SonicScope, proVISION, and TeleScope tools. The LWD data include downhole measurements of borehole caliper, resistivity at bit, annular pressure, gamma ray, velocity, porosity, bulk density, and nuclear magnetic resonance (NMR).
Processing
Depth shift: Original logs have been depth-shifted to the sea floor (-3532.2 m). The sea floor depth was determined by the step in gamma ray and resistivity values at the sediment-water interface.
Gamma Ray data processing: Processing of the data was performed in real-time onboard by Schlumberger personnel. Gamma Ray data is measured as natural Gamma Ray (GR): the GR from the RAB tool has been corrected for hole size (bit size), collar size, and type of drilling fluid.
NMR data processing: Processing of the data was performed onshore by Schlumberger personnel. The neutron porosity measurements have been corrected for standoff, temperature, mud salinity, and mud hydrogen index (mud pressure, temperature, and weight).
Sonic slowness data: Processing of the data was performed onshore by Schlumberger personnel. The sonic slowness data was sampled with a sampling rate of 0.1524 m (0.5 ft).
Resistivity data: The array resistivity compensated data was sampled with a sampling rate of 0.1524 m (0.5 ft). The RAB resistivity was sampled with a sampling rate of 0.03048 m (1.2 in).
Quality
Control
During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. The best data is acquired in a circular borehole; this is particularly true for the density tool, which uses clamp-on stabilizers to eliminate mud standoff and to ensure proper contact with the borehole wall. A data quality indicator is given by the ultrasonic caliper (UCAV) measurement of hole diameter. For NMR logs, the data quality is generally high when the distance between the tool sensor and the wall of the borehole is less than 1 inch. The data quality may be degraded when this distance is greater than 1 inch. The caliper log shows 1-2 inches of the washout for most of the logged interval, indicating moderate quality of the processed NMR data. The processed sonic slowness data (DTCO) is of good quality.
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:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-8777
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-8777
E-mail: Cristina Broglia