Chevron Gulf of Mexico Gas Hydrate JIP Drilling Program

Standard Wireline Data

JIP drilling contractor: Chevron

JIP logging contractor: Schlumberger

Hole: KC151-3

Expedition: 1

Location: Keathley Canyon (Gulf of MExico)

Latitude: 26° 49' 22.68" N (NAD27)

Longitude: 92° 59' 11.94" W (NAD27)

Sea floor depth (step in GR log): 1335 mbrf
Sea floor depth (drillers'): 1333.6 mbrf
Total penetration: 444.1 mbsf

 

 

Data

 

The logging data was recorded by Schlumberger in DLIS format. Data were processed by personnel at LDEO-BRG.

 

Logging Runs

Tool string Pass Top depth (mbsf) Bottom depth (mbsf) Pipe depth (mbsf) Notes
1.DSI/GPIT/SGT
Downlog
50
342
123
Uplog
0
333
123
Reference
2. VSI
Uplog
26 stations

The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor, see below).

 

Processing

 

Depth match and depth shift to sea floor: The downhole logs were depth-matched to the GR log from the uplog of the DSI/GPIT/SGT tool string, and were then shifted to the sea floor (- 1335 m). The uplog pass was chosen as the reference run because it was more comprehensive  and reached the sea floor.

Depth-matching is typically done in the following way: one log is chosen as reference (base) log (usually the total gamma ray log from the run with the greatest vertical extent and no sudden changes in cable speed), and then the features in the equivalent logs from the other runs are matched to it in turn. This matching is performed manually. The depth adjustments that were required to bring the match log in line with the base log are then applied to all the other logs from the same tool string.

The sea floor depth was determined by the step in gamma ray values at 1335 mbrf.). Generally, discrepancies may exist between the sea floor depth determined from the downhole logs and that determined by the drillers from the pipe length. In this case, there is a discrepancy of 1.4 m bethween the drillers' and the loggers' depths.

Acoustic data: The dipole shear sonic imager (DSI) was run in both passes in monopole and cross dipole modes.

 

 

Quality Control

 

The quality of the data is assessed by checking against reasonable values for the logged lithologies, by repeatability between different passes of the same tool, and by correspondence between logs affected by the same formation property (e.g. the resistivity log should show similar features to the sonic velocity log).

Gamma ray logs recorded through bottom hole assembly (BHA) and drill pipe should be used only qualitatively, because of the attenuation on the incoming signal. The thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.

A null value of -999.25 may  replace   invalid  log values.

Additional information about the drilling operations can be found in the cruise report. For further questions about the logs, please contact:

 

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia