Logging-While Drilling Processing
Coring and logging operator: MarE3
Hole: C0019H
Expedition: 405
Location: Japan Trench (NW Pacific Ocean)
Latitude: 37° 56' 20.424" N
Longitude: 143° 54' 47.442" E
Logging-while-drilling date: September 17-22, 2024
Sea floor depth (as seen on logs): 6925.7 mBRF
Total penetration: 7906 mBRF (980.3 m LSF)
Bit diameter: 8.5 in
Logging Tools
The downhole logs were recorded using the LWD/MWD (Logging-While-Drilling/Measurement-While-Drilling) system, which employs instruments that are part of the drill string itself. The advantages of this technique include being able to log in formations that would not provide a stable hole for wireline logging (e.g. the upper section of sedimentary formations) and logging a hole immediately during drilling, so that it is in good condition and largely free of wash-outs. The data is recorded in the tool's memory and downloaded when the drill string returns to the rig floor. A small subset of the data is transmitted up to the ship during drilling.
The following tools were deployed in Hole C0019H:
sonicScope (acoustic velocity data) / telescope (real-time transmission, deviation, inclination, pressure, temperature) / microScope (resistivity, resistivity images, gamma ray)
Data were recorded primarily during drilling, going down, but a subset of data was also recorded going up in the deepest section of the hole (7784 - 7540 mBRF) while reaming/recovering the tools.
The processing and all related documentation were coordinated and/or produced by the Logging Staff Scientists (LSS) of IODP Expedition 405.
Processing
Environmental corrections (SLB): gamma ray was environmentally corrected for bit size, tool size and mud weight. Resistivity was environmentally corrected for bit size, mud resistivity and bottom hole temperature.
Note on Bit Resistivity (RES_BIT and RES_BIT_RAW) (SLB): The curves from bit resistivity were initially delivered with a depth shift (of approximatively 6 m down compared to the other resistivity curves) due to unidentified errors in tool settings or processing. For the final data delivery, SLB delivered shifted RES_BIT_S curves.
Sonic processing and picking (SLB): onshore processing made by SLB was performed by intervals, where the best method (monopole high MH, monopole low leaky-P MLLP, quadrupole QP) insured the best picking. SLB notes and comments about their processing are available in the PDF sonic field log plots. Slowness logs (e.g. DTCO, DTSH) were delivered by interval (method-dependent), and as merged logs combining different intervals. Combined slowness logs were converted to velocity (VP and VS when available) by the LSS team.
Depth shift (LSS/TechLog): The original logs have been depth shifted to the sea floor (-6925.7 m) by the Logging Staff Scientist team.
Image processing (LSS/TechLog): resistivity images were oriented using the final survey data, the dynamic scale image was performed using a 5 m window.
Note on DLIS depth sampling rate unit and TechLog: DLIS datasets and metadata include properties about the sampling rate of each DLIS frame. Depending on the SLB team that provided original data, the DLIS files had a set depth sampling rate in imperial or metric system. These properties have been edited in the processed DLIS to remain in metric system during import and export in Techlog.
Quality Control
During the processing, quality control of the data is performed by inter-comparison of all logging data to ensure that reasonable values are returned for expected lithology types and features on the logs reflect true formation characteristics and are not artefacts. SLB recommendations for ensuring good electric images from microScope is to keep a ratio ROP(m/hr)/RPM(m/min) < 0.6, allowing some stick and slip and depth variation. SLB field engineers worked closely with the drilling team to keep an optimal ratio ROP/RPM during drilling operations. The overall quality of the logging data is good.
Additional information about the drilling and logging operations can be found in the Operations and Logging-while-drilling sections of the expedition report, Proceedings of the International Ocean Discovery Program, Expedition 405.
For questions about the logs, please contact:
Adam Wspanialy
E-mail: wspanialya@jamstec.go.jp
Erwan Le Ber
E-mail: erwan.le-ber@umontpellier.fr // elb51@le.ac.uk
Marisa Rydzy
E-mail: mbr8@leicester.ac.uk
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.