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doi:10.2204/iodp.proc.314315316.112.2009

Onboard data flow and quality check

For each operation, two types of data are collected: (1) real-time data that include all MWD-APWD data and selected LWD data and (2) LWD data that have been recorded downhole and stored in the tool’s memory. Data are originally recorded downhole at a preset frequency. The depth version is obtained after merging the time (downhole) with the time-depth relationship recorded on the surface by the IDEAL system. For the MWD-APWD, adnVISION, and geoVISION tools, both time and depth versions of the data exist. The raw sonicVISION data were only distributed versus depth and were processed onboard by the DCS specialist. In the same way, the seismicVISION data (check shots) were only available versus depth and distributed to the Shipboard Science Party for immediate processing and analysis. The time version of the data was made available in log ASCII standard (LAS) format. The depth version of the data was made available in digital logging interchange standard (DLIS) format for the MWD-APWD, adnVISION, geoVISION, and sonicVISION tools and in Society of Exploration Geophysicists standard (data format “Y”) for the seismicVISION tool.

After determining the position of the mudline by identifying a break in the gamma ray log (and resistivity logs, when available), the data were depth shifted to the seafloor (LWD depth below seafloor [LSF]). The depth-shifted version of the MWD-APWD, adnVISION, geoVISION, and processed data were distributed in the native format (DLIS), and the main scalar logs were extracted and converted into LAS files. All files (time based, depth based, original, and depth shifted) and associated documentation (quality check and operation reports) were distributed to the Shipboard Science Party through the onboard intranet data servers. Analyses, integration results, and reports produced by the Shipboard Scientific Party were then archived on the server for further distribution. Normal data flow is illustrated in FigureF8.

The Logging Staff Scientist performed initial conversion and output of the raw data received from the Wellsite Geologist, who received the data from the Schlumberger LWD engineer. Logging Staff Scientist duties include documentation of the MWD-APWD-LWD operations, data quality assessment (highlighting any abnormalities), depth shifting (i.e., converting depth below rig floor to depth below seafloor), and systematic distribution and documentation of data. Operations and quality assessment are described in two main plots (data versus time and data versus depth) related by a third time-depth relationship plot (Fig. F9). In the first plot (Plot 1), time-depth relationship (Panel 1.1), surface drilling and downhole parameters (Panel 1.2), and selected geophysical logs (Panel 1.3) are plotted versus time to identify the sequence of drilling events and further assess their possible impact on data quality. In the second plot (Plot 2), the time-time relationship (Panel 2.1) and operational surface and downhole data (Panel 2.2) are reported versus depth for large-scale assessment of drilling conditions on data quality. These first panels are completed by detailed analysis of the ultrasonic caliper, density, correction on bulk density, and comparison of the shallow and deep button resistivity scalar logs to further assess hole condition (cave, washout, or bridge) and possible impact on density/​porosity data, as well as invasion (Panel 2.3). Elapsed time of the main geophysical measurements after bit is also indicated in this third panel. In a fourth panel (Panel 2.4), changes in parameters of the sonic processing and a quality indicator of the resulting processed sonic log are documented. Finally, results of detailed quality assessment of borehole images (mostly shallow, medium, and deep button resistivity and gamma ray images) are documented in the last panel (Panel 2.5). The third time-depth relationship plot (Plot 3), made at the same scale as the two main time and depth plots, allows easy navigation between those two plots.

Quality of MWD-APWD-LWD data is mostly assessed by cross-correlating available logs. Available logs are of two types, as follows:

1. Drilling control logs including surface drilling surface parameters (e.g., ROP, surface weight on bit [SWOB], hook load [HKLD], standpipe pressure [SPPA]), and downhole drilling parameters (e.g., collar [bit] rotation [CRPM], hole deviation [HDEVI], radial shock rate [SKR_R], tangential shock rate [SKR_T], shock peak [SHKPK], and stick-slip indicator [SLIP]) and
2. Geophysical control logs such as calipers (ADIA, ECAL_RAB), gamma ray (GR), annular pressure (APWD), and temperature (ATMP_MWD).

Geophysical logging data may be degraded where borehole diameter greatly increases or is washed out. Deep investigation measurements such as resistivity and sonic velocity are least sensitive to borehole conditions. Nuclear measurements (density and neutron porosity) are more sensitive because of their shallow depth of investigation and the effect of drilling fluid volume on neutron and gamma ray attenuation. Corrections were applied to the original data to reduce these effects. The effects of very large washouts, however, cannot be corrected.

Azimuthal measurements and associated images are of low quality when the tool is not rotating (slip) or when its rotation exceeds 250 rpm. In zones of high stick-slip, even if tool rotation (CRPM) is set to a typical value of 100 rpm, CRPM can greatly vary locally (and exceed 250 rpm), resulting in images of lower quality. As all measurements even by the same tool are not sampled at the same time (sampling rate of adnVISION and geoVISION = 5 s), improper heave compensation and irregular movement of the BHA (vibration shocks or bending) can result in local depth shift between measurements by several tens of centimeters.

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