Logging-While-Drilling Data Processing

IODP logging contractor: USIO/LDEO

Hole: U1379A

Expedition: 334

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 (driller's): 137 m DRF

Sea floor depth (logger's): 133 m LRF (from adnVISION and arcVISION)

Total penetration: 1103 m LRF (966 m LSF)

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 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.






Depth 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. Note that this differs 4 m from the seafloor depth tagged by the drillers at 137 m DRF.


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.


Neutron 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).

Density 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. Density data are available with two sampling rates: 0.1524 m (0.5 ft) and 0.0305 m (1.2 in). A porosity curve (DPHI) has been calculated from the IDRO curveusing a matrix density of 2.65 g/cc and a fluid density of 1.025 g/cc. This is included in the composite plot available online.



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 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:


Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia