Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1351B

Expedition: 317

Location: Canterbury Basin (SW Pacific Ocean)

Latitude: 44 °53.0422' S

Longitude: 171° 50.406 ' E

Logging date: November 24-25, 2009

Sea floor depth (driller's): 132.7 m DRF

Sea floor depth (logger's): 134 m WRF (DIT/APS/HLDS/HNGS downlog)

Sea floor depth (logger's): 132.5 m WRF (DIT/APS/HLDS/HNGS main and repeat)

Sea floor depth (logger's): 133 m WRF (FMS/DSI/GPIT/HNGS downlog)

Total penetration:  1030.6 m DSF

Total core recovered: 304.52 m ( 29.5 % of cored section)

Oldest sediment recovered: Late Miocene

Lithologies:  mud, sandy mud, shell hash, sand, muddy sand, sand (sandstone), shell hash (limestone)

 

Data

 

The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in November 2009.

 

Logging Runs

Tool string Pass Top depth (m WMSF) Bottom depth (m WMSF) Pipe Depth (m WMSF) Notes
1.DIT/APS/HLDS/GPITHNGS
Downlog
0
969
82

HLDS not valid

Main
0
1029
82
Reference
Repeat
872
1029
Open Hole
2. FMS/DSI/GPIT/HNGS
Downlog
0
487
82
Calipers closed
Uplog
73
484
81

 

The hole was drilled to a total depth of 1030.6 m DSF. Minor drag on the drill string was reported by the driller over the lower portion of the hole (below 800 m DRF), but no overpulls or significant sticking, so the logging was conducted without a wiper trip in order to maximize hole quality. The logging operation was started with the DIT/APS/HLDS/GPIT/HNGS tool string for three passes, then followed by the FMS/DSI/GPIT/HNGS tool string for two passes. The average heave of the vessel was less than 0.3 m, so wireline heave compensator was not used.

 

The depths in the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). Generally, discrepancies may exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from a 'bottom felt' depth in soft sediment.

 

Processing

 

Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (-134, -132.5, m WRF for DIT/APS/HLDS/GPIT/HNGS downlog, main and repeat passes respectively, and 133.5 m WRF for the two FMS/DSI/GPIT/HNGS passes). The sea floor depth was determined by the step in gamma ray values observed on the logs. The depth-shifted logs were then depth-matched to those of the DIT/APS/HLDS/GPIT/HNGS main pass (reference).

 

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.

 

Environmental corrections. The HNGS data were corrected for hole size during the recording. The APS and HLDS data were corrected for standoff and hole size respectively during the recording.

 

High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded at sampling rates of 2.54 and 5.08 cm, respectively, in addition to the standard sampling rate of 15.24 cm. The enhanced bulk density curve is the result of Schlumberger enhanced processing technique performed on the MAXIS system onboard. While in normal processing short-spacing data is smoothed to match the long-spacing one, in enhanced processing this is reversed. In a situation where there is good contact between the HLDS pad and the borehole wall (low-density correction) the results are improved, because the short spacing has better vertical resolution.

 

Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes in both passes: P&S monopole (medium frequency), upper dipole (standard frequency), and lower dipole (low frequency). Because of the slow formation, the automatic picking of wave arrivals in the sonic waveforms did not provide consistently reliable results. Reprocessing of all the original waveforms was performed to validate the original data or extract meaningful compressional and shear velocities. The most reliable shear velocity value is the one derived from the lower dipole (VS1), where the lower source frequency used generated more cohert waveforms.

 

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 of the incoming signal. The thick-walled BHA attenuates the signal more than the thinner-walled drill pipe. The slightly stronger gamma ray signals from HNGS (FMS) compared to that from HNGS (DIT) are likely due to the residual radiation of the HLDS minitron from the main pass. Note that, because the minitron was on during the down run between repeat and main passes of the triple combo tool string, the first ~ 10 meters (1005 - 995 m WMSF) of gamma ray data from the main pass are invalid (i.e., too high).

Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (APS, HLDS). The caliper logs indicate that, except for the depth interval of 214 - 170 m WMSF, the rest of the borehole was washed out to the degree (>19") where it can adversely affect the tool response. Thus, density and porosity logs in most part of this borehole should be used with caution.

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

Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition reports, Proceedings of the Integrated Drilling Program, Expedition 317. For further questions about the logs, please contact:

 

 

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia

 

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu