IODP logging contractor: USIO/LDEO
Location: Costa Rica Pacific Margin - CRISP (equatorial NE Pacific)
Latitude: 8° 40.8501 ' N
Longitude: 84° 2.0166' W
Logging-while-drilling date: March 20-23, 2011
Sea floor depth (logger's): 133 m LRF (from adnVISION and arcVISION)
Total penetration: 1103 m LRF (966 m LSF)
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.
following LWD/MWD tools were deployed in Hole U1379A:
adnVISION 675 (density, porosity, caliper)
arcVISION (resistivity, gamma ray, temperature, pressure)
geoVISION 675 (RAB resistivity and gamma ray)
TeleScope 675 (MWD tools, power and real-time transmission)
All tools are 6 3/4 in. in diameter in a BHA with 8 1/2 in. bit and 6 1/2 in. drill collars.
The drilling of hole U1379A proceeded smoothly with an almost with overall drilling rates of 8-15 m/hr. The sediment-basement interface was reached at about 893 m LSF; the basement was drilled and logged to a total depth of 966 m LSF, which exceeded by 75 m the original depth objective. A problem with the geoVISION data was observed by the Schlumberger engineers during the time-depth processing performed onboard; this processing could not be run because of an improper recording of time by the geoVISION clock. Since the data was otherwise good, it was sent to the Schlumberger Houston processing center to be corrected, but efforts to address the data acquisition problems were not successful. No geoVISION data are available for Hole U1379A.
shift: The original logs
have been depth shifted to the sea floor (- 133 m). The sea floor depth was
determined by the step in the density log from the adnVISION tool and arcVISION gamma ray.
Gamma Ray data processing: Processing of the data is performed onboard by Schlumberger personnel after downloading of the data from the tool. Gamma Ray data is measured as Natural Gamma Ray (GR): the GR from the arcVISION tool has been corrected for hole size (bit size), collar size, and type of drilling fluid.
porosity data processing: The
neutron porosity measurements have been corrected for standoff, temperature,
mud salinity, and mud hydrogen index (mud pressure, temperature, and weight).
The porosity data are available with a sampling rate of 0.1524 m (0.5 ft).
data processing: Density
data have been processed to correct for the irregular borehole using a
technique called 'rotational processing', which is particularly
useful in deviated or enlarged borehole with irregular or elliptical shape.
This method measures the density variation while the tool rotates
in the borehole, estimates the standoff (distance between the tool and the
borehole wall), and corrects the density reading.
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 that features on the logs reflect true formation characteristics
and are not artifacts. The best data are acquired in a circular borehole; this
is particularly true for the density tool, which uses clamp-on stabilizers to
reduce standoff and to ensure proper contact with the borehole wall. A
data quality indicator is given by the hole diamtere, measured by the density caliper (DCAV) and by the ultrasonic caliper measured along four axes (1-5,2-6,3-7 and 4-8); the calculated average of the ultrasonic measurements is given by the UCAV (ultrasonic caliper average). Another quality indicator is represented by the density
correction (DRHO and IDDR).
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 Integrated Drilling Program, Expedition 334. For further questions about the logs, please contact:
E-mail: Tanzhuo Liu
E-mail: Cristina Broglia