Wireline Standard Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 1065A
Leg: 173
Location: Iberian Abyssal Plain (NE Atlantic)
Latitude: 40° 43.4469' N
Longitude: 11° 17.7236' W
Logging date: April, 1997
Bottom felt: 4781 mbrf
Total penetration: 617 mbsf
Total core recovered: 46.5 m (12.4 %)
Logging
Runs
Logging string 1: DIT/HLDT/APS/HNGS (main and repeat)
Logging string 2: FMS/SDT/GPIT/NGT
Wireline heave compensator was used to counter ship heave.
Bottom-hole
Assembly
The following bottom-hole assembly depths are as they appear on the logs after differential depth shift (see "Depth shift" section) and depth shift to the sea floor. As such, there might be a discrepancy with the original depths given by the drillers onboard. Possible reasons for depth discrepancies are ship heave, use of wireline heave compensator, and drill string and/or wireline stretch.
DIT/HLDT/APS/HNGS: Bottom-hole assembly at ~ 106 mbsf (main and repeat)
FMS/SDT/GPIT/NGT: Recorded open-hole.
Processing
Depth shift: Original logs have been interactively depth shifted with reference to HNGS from DIT/HLDT/APS/HNGS repeat run and to the sea floor (- 4779 m). This water depth value corresponds to the depth of the mudline as observed on the logs and as such it differs 2 m from the "bottom felt" depth given by the drillers. Due to the bad hole conditions, depth correlation among runs is often difficult and therefore this should be taken into account when comparing data from different runs. The program used is an interactive, graphical depth-match program which allows to visually correlate logs and to define appropriate shifts. The reference and match channels are displayed on the screen, with vectors connecting old (reference curve) and new (match curve) shift depths. The total gamma ray curve (SGR) from the NGT tool run on each logging string is used to correlate the logging runs most often. In general, the reference curve is chosen on the basis of constant, low cable tension and high cable speed (tools run at faster speeds are less likely to stick and are less susceptible to data degradation caused by ship heave). Other factors, however, such as the length of the logged interval, the presence of drill pipe, and the statistical quality of the collected data (better statistics is obtained at lower logging speeds) are also considered in the selection. A list of the amount of differential depth shifts applied at this hole is available upon request.
Gamma-ray processing: NGT data from the FMS/GPIT/SDT/NGT runs have been processed to correct for borehole size and type of drilling fluid. HNGS data from the DIT/APS/HLDT/HNGS tool string were corrected in real-time during the recording.
Acoustic data processing: The array sonic tool was operated in standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') and short-spacing (3-5-5-7') logs. Because of the extremely noisy character and low quality of the sonic logs, no processing has been performed at this stage. Processing of full sonic waveforms is recommended in order to get better results. Un-compensated velocity values have been calculated from edited the LTT2 (8 ft spacing) and should be used qualitatively only.
High-resolution data: No high resolution data was recorded in Hole 1065A.
Quality
Control
During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. The large (15" over most of the logged interval) and irregular borehole affects most recordings, particularly those that require eccentralization (APS, HLDT) and a good contact with the borehole wall. Both density and neutron porosity data recorded at this hole appear to be of very poor quality, due to the lack of proper eccentralization during both the main and the repeat pass. The standoff data clearly shows that the tool was not in contact with the borehole wall during most of the recording. Due to tool failure during the main pass, neutron porosity (APS) data was recorded only up to 325 mbsf; during the repeat pass the APS tool was fully functional. HLDT density data was collected during the entire main pass but only in the section below 325 mbsf the caliper worked and allowed for the correction for borehole size. Above this depth, the tool could not be properly eccentralized as the caliper arm was closed due to tool string sticking problems. Hole deviation can also affect the data negatively; the FMS, for example, is not designed to be run in holes deviated more than 10 degrees, as the tool weight might cause the caliper to close. Even though both density and neutron data are presented, extreme caution should be exercised when using them.
Data recorded through bottom-hole assembly, such as the HNGS data above 106 mbsf, should be used qualitatively only because of the attenuation on the incoming signal.
Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI) and on the FMS string (C1 and C2). Due to tool string sticking problems, the former was used only during the repeat pass of the DIT/HLDT/APS/HNGS tool string; it indicated that the hole was greater than 15", with a standoff often as high as 1". The latter indicated as well that the hole was, for the most part, larger than the maximum caliper reading of the FMS (15"). This greatly affected the quality of the FMS and acoustic data recorded.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 173. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia