Logging-While-Drilling Data Processing


Operator and logging contractor: LDEO-BRG

Hole: 5A (proposed site KGGH02-A)

Expedition: NGHP-1

Location: Krishna-Godavari Basin, Eastern India (Bay of Bengal)

Latitude: 16° 1.722' N

Longitude: 81° 2.678' E

Logging date: May 24-25, 2006

Sea floor depth (drillers'): 963 mbrf

Sea floor depth (loggers'): 956 mbrf

Total penetration: 1163 mbrf (200 mbsf)

Lithology: Nannofossil-rich clay with occasional thin silt beds and abundant carbonatic nodules (from Hole 5C)


Logging Tools


The logs were recorded using the LWD (Logging-While-Drilling) system, which allows the acquisition of open-hole logs using 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 after it is drilled, so that it is in good condition and largely free of wash-outs.

The following LWD tools were deployed in Hole 5A:


EcoScope (phase and attenuation resistivity, density, porosity, geochemistry, gamma ray, temperature and pressure)

geoVision (resistivity-at-the-bit and gamma ray)

sonicVision (velocity)

TeleScope (drilling parameters)


In Hole 5A, the rate of penetration was approximately 20 m/hr.




Depth shift: The original logs have been depth shifted to the sea floor (- 956 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 is performed in real-time onboard by Schlumberger personnel. Gamma Ray data is measured as Natural Gamma Ray (GR): the GR from the GVR 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).


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 statistical 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 (a more detailed description of this technique is available upon request).


Resistivity data: The GVR resistivity is sampled with a 0.03048 m (1.2 in) sampling rate. The ARC resistivity is sampled with a 0.1524 m (0.5 ft) sampling rate.



Quality Control


During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. The best data are 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 density caliper (DCAV) measurement of hole diameter. Another quality indicator is represented by the density correction (DRHO).


For further questions about the processing, please contact:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia