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Publications > Expedition Publications > Logging Summaries

Logging Summaries

IODP Expedition 317:

Canterbury Basin Sea Level

Expedition 317 Scientific Party

Introduction

    Figure 1. Location of IODP Expedition 317 off the east coast of the South Island of New Zealand.

    Figure 2. Seismic line (EW00-01-66) showing the position of Expedition 317 sites along the shelf-to-slope transect. Site U1352 (dashed line), located ~5.8 km northwest of Line 66, is projected onto the line.

    The primary objective of Expedition 317 was to understand the relative importance of global sea level versus local tectonic and sedimentary processes in controlling sedimentary cycles on the continental margin. The expedition recovered sediments from the Eocene to recent period, with a particular focus on the sequence stratigraphy of the late Miocene to recent, when global sea level change was dominated by glacioeustasy. The Canterbury Basin, off the South Island of New Zealand, provides a unique environment to study the complex interactions between sedimentary processes because of the proximity of an uplifting mountain chain (the Southern Alps), high rates of sediment supply, and strong ocean currents.

    During Expedition 317, a shelf-to-slope transect of four sites was drilled in the Canterbury Basin (see Figure 1). The transect provides access to a stratigraphic record of depositional cycles across the shallow-water environment , which is most directly affected by relative sea level changes (see Figure 2). Lithologic boundaries and significant downhole variations that are provisionally correlative with seismic sequence boundaries have been identified in the three continental shelf sites (landward to basinward, Sites U1353, U1354, and U1351) and slope Site U1352. These data will be used to estimate the timing and amplitude of past global sea level changes and to document the sedimentary processes that operate during sequence formation, as well as providing insights into the origins of seismically resolvable sequences.

    One of the primary objectives of the logging program was to provide precise seismic-well correlations to constrain the seismic stratigraphy of the Canterbury Basin. Logging data were also critical for identifying the nature of key seismic reflections and unconformities, which could potentially coincide with intervals that would be difficult to recover using standard coring techniques.

    A complete overview of the expedition operations and preliminary scientific results is available in the Expedition 317 Preliminary Report.

     

Logging Tools and Operations

    Figure 3. Logging tool strings planned for Expedition 317. Some of the tool strings were reduced or reconfigured during the expedition, due to difficult hole conditions.

    The planned logging program included three logging tool strings for each site: the triple combo, the FMS/Sonic tool string, and the VSI tool string for vertical seismic profiles. Figure 3 shows the tool strings originally planned for deployment at the four primary sites of Expedition 317.

    Six holes were logged during Expedition 317: Holes U1351B, U1351C, U1352B, U1352C, U1353C, and U1354C. Hole preparation consisted of sweeping the hole with high-viscosity sepiolite/attapulgite mud, circulating twice the volume of the hole, and displacing the hole with mud or seawater. Borehole conditions were unstable at all drilled sites, particularly in the shallow intervals dominated by unconsolidated sand- and shell-rich sediments. As a result of collapsing and obstructed boreholes, many of the logging runs were unable to reach total depth and tool strings became stuck in two of the six holes logged (Holes U1351C and U1353C). The logged intervals at each site, compared to the total borehole depths, are shown in Figure 4.

    Figure 4. Logged intervals and tool strings run for each hole during Expedition 317. Intervals include logging through drill pipe between the seafloor and the drill bit, for which only gamma ray data is reliable. Pipe depth for each hole is indicated by horizontal dashed line.

    The triple combo and FMS/Sonic tool strings were run in at least one hole at Sites U1351, U1352, and U1353. Because of unstable hole conditions, the triple combo was run without radioactive sources in two holes, so no density or neutron porosity logs were recorded in these holes. A single modified tool string, the Sonic combo, was run at Site U1354 due to the potential for unstable hole conditions and limited time at the end of the expedition. Because of unstable hole conditions and large borehole diameters at all sites, it was not feasible to deploy the VSI tool string, which requires the tool to be firmly anchored against the borehole wall to record good waveforms.

    The following table summarizes logging operations carried out during the expedition.

     

     

     

Data and Results

    Overview

    We present here a summary of logging data collected during this expedition and show some highlights for each site. The base of the drill pipe was lowered to ~80-100 meters below the seafloor prior to logging, so wireline logs are generally recorded only below this depth. Although logging data are initially referenced to depth below the rig floor (WRF), after logging is completed, all data are shifted to a sea floor reference and depth-matched to remove offsets between different logging runs. The resulting depth scale is wireline matched depth below sea floor (WMSF) and all log data presented here are in meters WMSF.

    Porosity and density from resistivity

    In order to provide a measure of porosity and density for sites where poor hole conditions adversely affected density and neutron porosity measurements (U1352) or where the triple combo was run without radioactive sources (U1353 and U1354), we used Archie’s (1942) relationship to calculate porosity. Although electrical resistivity is not a direct measurement of porosity, it is highly sensitive to the presence of formation fluid and, therefore, to bulk porosity. Archie (1942) established an empirical relationship between porosity, formation resistivity, and pore water resistivity in sandy formations, but it has also been successfully used to estimate porosity in clay-rich formations with poor borehole conditions (Jarrard et al., 1989; Collett, 1998). For Expedition 317, porosity was calculated from the deep induction resistivity log (IDPH), because it is the log least affected by borehole conditions (Schlumberger, 1989), and combined with grain density from moisture and density (MAD) measurements on cores to derive a more reliable density profile.

    See the Proceedings of IODP Expedition 317 for a complete description of calculations for each site, including values for Archie coefficients and temperature and salinity estimations.

    Synthetic seismograms

    In order to correlate features in seismic stratigraphy, recorded in the time domain, to features in cores and logs, recorded in the depth domain, a time-depth relationship must be determined at each site. The time-depth relationship can be estimated by constructing synthetic seismograms, which are computed from reflection coefficients obtained from contrasts in compressional wave velocity and density, to match the seismic traces nearest to the borehole. Synthetic seismograms were constructed for sites where shipboard sonic logs provided reliable compressional wave velocity (U1352, U1353, and U1354), using the IESX seismic interpretation package (part of the Schlumberger GeoFrame software suite). Typically, the synthetic seismograms provided a very good match with reflections interpreted as sequence boundaries in the seismic stratigraphy, as shown in site figures.

     

    Site U1351

    Figure 5. Summary of logging data recorded with the Triple Combo at Site U1351.

    Figure 6. Summary of logging data recorded with the FMS/Sonic at Site U1351.

    Site U1351 was drilled as the deepest of three sites on the continental shelf, at 122 meters water depth. The primary objective at this site was to sample facies just landward of clinoform breakpoints in progradational seismic sequence boundaries, linking shelf and slope unconformities (middle Miocene to Holocene). Core recovery in the three holes drilled at this site ranged from 30% to 98%, with lowest recovery deeper than ~80 meters below sea floor. Sediments recovered at this site correspond to two lithologic units: Unit I (0-262 mbsf), consisting of mud and sandy mud with lesser amounts of shell hash and sand; and Unit II (262-1024 mbsf), consisting of sandy mud and muddy sand with lesser amounts of sand and shell hash.

    Downhole logs were recorded in Holes U1351B and logging-dedicated U1351C. The caliper logs recorded by the HLDS and FMS at this site show that the borehole was significantly larger than bit size above ~500 WMSF and less enlarged but very irregular below ~500 WMSF (see Figure 5 and Figure 6). Comparison of measurements between Holes U1352B and U1352C show very good agreement, even in the enlarged upper half of the hole, indicating that the density log was not seriously affected by the hole condition. Below ~620 WMSF, none of the questionable low gamma ray and resistivity excursions in Hole U1351B are matched in Hole U1351C, suggesting that they resulted from the irregular hole in the deeper section of Hole U1351B. High coherence in sonic logs suggests that the DSI should provide reliable velocity values; however, the automatic labeling of wave arrivals failed to recognize the compressional wave in some intervals. Additional post-cruise processing should correct these curves and allow for the construction of a synthetic seismogram.

    Three logging units were identified at this site, based on subtle changes in trends and characteristic features. Logging Unit 1 (83-260 WMSF) is characterized by relatively high-amplitude variations in gamma ray, with low gamma ray excursions corresponding to intervals with high resistivity and sonic velocity values. These are likely sand- and/or shell-rich layers, which is consistent with poor core recovery in these intervals. The overall log signature in this unit is indicative of alternating shelly or sandy beds and clay-rich beds. Logging Unit 2 (260-510 WMSF) is defined by low-amplitude variability and decreasing trends with depth in gamma ray and resisitivity. Three distinct intervals of increasing upward gamma ray within this unit suggest fining-upward subunits. Caliper readings consistently larger than 18.5 inches in Units 1 and 2 suggest that the formation has little cohesion. The top of Logging Unit 3 (510-1031 WMSF) is defined by a significant increase in gamma ray, accompanied by increases in density and resistivity. Below a ~50 m thick interval with high gamma ray, density, and resistivity values, the logs are variable and without clear trends. Logging Unit 3 corresponds to an interval where the borehole diameter is slightly smaller than in the upper units, suggesting more consolidated or cohesive sediments.


    Site U1352

    Figure 7. Summary of logging data recorded at Site U1352.

    The critical objectives of drilling at Site U1352 (at 344 meters water depth) were to sample slope facies of seismic sequence boundaries (middle Miocene to Holocene) as well as the Marshall Paraconformity, interpreted to be the result of intensified current erosion in the early Oligocene that accompanied the initiation of thermohaline circulation and the proto Antarctic Circumpolar Current following the separation of Australia and Antarctica. Core recovery was ~100% in the two shallow holes (<130 m penetration) and ranged from 51% to 74% in the two deep holes drilled at this site. Sediments recovered at this site correspond to three lithologic units: Unit I (0-711 mbsf), consisting of calcareous sandy mud, interbedded sandy mud and clay, interbedded sand and mud, massive sand, mottled sandy mud, homogenous mud, sandy mud, and marl; Unit II (711-1853 mbsf), consisting of calcareous sandy mud, sandy marls, chalk, sandy marlstone, and sandy limestone; and Unit III (1853-1924 mbsf), consisting of pelagic foraminifera-bearing nannofossil limestone.

    Downhole logs were recorded in Holes U1352B and U1352C.  Caliper logs from this site suggest an enlarged and irregular borehole for the entire logged interval (see Figure 7). Measurements from the two orthogonal FMS calipers suggest that the borehole cross-section was not circular, but likely elliptical below ~270 WMSF. Despite the enlarged borehole, comparison between gamma ray logs and natural gamma ray (NGR) measurements made on cores from Hole U1352B shows generally good agreement. However, the density log is seriously affected by the hole conditions, shown by the lack of agreement between logs and MAD core measurements. High coherence in the sonic waveforms suggests that the DSI data should provide reliable compressional and shear velocity values.

    The combined analysis of the logs allows for the identification of two logging units at this site, based on characteristic trends. Logging Unit 1 (82-250 WMSF) is characterized by relatively low-amplitude variations in gamma ray, resistivity, and acoustic velocities. There is a distinct increasing-upward trend in gamma ray from 250 WMSF up to a high gamma ray interval between 160-170 WMSF, which corresponds to an interval of homogeneous mud with clay beds in cores from Hole U1352B. Gamma ray values decrease upward above ~160 WMSF, which may reflect a generally decreasing clay content in this depth interval. The increasing-upward and then decreasing-upward pattern in gamma ray is consistent with gamma ray logs from an equivalent depth at nearby ODP Site 1119 (Shipboard Scientific Party, 1999). Logging Unit 2 (250-487 WMSF) is defined by a change to higher-amplitude variations in gamma ray, resistivity, and acoustic velocities. Gamma ray and velocity increase with depth. The borehole diameter in this unit is smaller but highly irregular, which may reflect the presence of more cohesive marls in the formation.

     

    Site U1353

    Figure 8. Summary of logging data recorded with the triple combo at Site U1353.

    Figure 9. Summary of logging data recorded with the FMS/Sonic and synthetic seismogram at Site U1353. 

    Site U1353 was the shallowest site drilled on the continental shelf, at 85 meters water depth. The primary objective of drilling at this site was to sample facies landward of clinoform breakpoints of seismic sequence boundaries, particularly the older unconformities (middle Miocene to Pliocene). Core recovery ranged from ~100% in the shallow hole (<60 m penetration) to 34% in the deep cored hole at this site. Sediments drilled at this site correspond to two lithologic units: Unit I (0-151 mbsf), consisting of mud with minor amounts of very fine sand, and Unit II (151-614 mbsf), consisting of very fine sandy mud and mud, typically with shells.

    Downhole logs were recorded in logging-dedicated Hole U1353C. While caliper logs from both HLDS and FMS indicate an enlarged and irregular borehole, all calipers maintained relatively good contact with the formation above ~350 WMSF and suggest that recorded data should be of good quality (see Figure 8 and Figure 9). Below this depth, hole diameter is close to the maximum reach of the HLDS caliper. The closely matched overlay between the two resistivity measurements with deep and medium depths of penetration indicates that the resistivity log is of good quality. Comparison of the gamma ray log with NGR core data also shows significant agreement, indicating good quality gamma ray log values. Clear arrivals and high coherence patterns in sonic logs indicate that the DSI should provide reliable velocity values.

    Two logging units were identified, based on combined analysis of the logs. Logging Unit 1 (105-260 WMSF) is characterized by an increasing-upward trend in gamma ray between ~250 and 180 WMSF, followed by a generally decreasing-upward trend from 180 WMSF to the top of the unit. These trends are interrupted by abrupt high-amplitude lows in gamma ray and peaks in resistivity and velocity that are interpreted as sandy intervals, many of which coincide with sand or gravel at corresponding depths in cored Hole U1353B. These features also show good correspondence with significant seismic reflections (see Figure 9). Logging Unit 2 (260-528 WMSF) is characterized by overall decreasing trends with depth in gamma ray and resistivity, with low variability. The top of the unit is roughly the same depth as the onset of low core recovery in Hole U1353B and the point at which the FMS/Sonic tool string encountered an impassable obstruction, suggesting a change in the properties of the formation across the unit boundary.

     

    Site U1354

    Site U1354, an intermediate depth shelf site at 120 meters water depth, was drilled with the primary objective of sampling facies landward of breakpoints of seismic sequence boundaries, particularly near the breakpoints of several late Miocene to Pliocene unconformities. Core recovery ranged from ~100% in shallow holes (<90 m penetration) to 42% in the deeper hole. Sediments drilled at this site correspond to two lithologic units: Unit I (0-251 mbsf), consisting of calcareous muddy sand, sandy marl, and homogenous marl and very well-sorted very fine to fine sand; and Unit II (251- 375 mbsf), consisting of very fine sandy mud and mud, typically with shells.

    Figure 10. Summary of logging data recorded with the Sonic Combo at Site U1354.

    Downhole logs were recorded in Hole U1354C with a single, modified tool string (dubbed the “Sonic Combo”, HNGS/DSI/GPIT/DIT), due to the potential for unstable hole conditions and time constraints at the end of the expedition. No caliper was run in this toolstring, but data quality was assessed by looking at correlations between different measurements, internal consistency, and comparisons between logs and core measurements. Significant increases in resistivity and velocity are accompanied by negative gamma ray excursions (see Figure 10), indicating that those intervals were likely consolidated sand-rich layers and that the changes in gamma ray represent valid lithology changes rather than intervals of enlarged borehole. A comparison with logs recorded at other shelf sites (Sites U1351 and U1353) also shows that the trends in gamma ray can be visually correlated across the shelf, indicating the good quality of logs recorded in Hole U1354C. There is a reasonable agreement between the gamma ray logs and NGR measurements on cores from Hole U1354C. The good agreement between the deep-penetration and medium-penetration resistivity curves is yet another indication that the borehole diameter was not anomalously large or irregular.

    The combined analysis of logs was used to identify two logging units defined by characteristic trends. Logging Unit 1 (110-285 WMSF) is characterized by an increasing trend in gamma ray from the top of the unit to ~185 WMSF, followed by a generally decreasing trend to the base of the unit, punctuated by abrupt high-amplitude lows in gamma ray and peaks in resistivity and velocity. This unit is identical to Logging Unit 1 at Site U1353 and the high-amplitude features at both sites correspond to coarser-grained intervals in cores. Preliminary synthetic seismograms show that the two most prominent of these sand-rich intervals coincide with seismic reflectors U10 and U11. Logging Unit 2 (285-384 WMSF) is characterized by slightly decreasing trends in gamma ray and resistivity, with limited variability, and increasing velocity. It is similar to Logging Unit 2 at Site U1353, which is characterized by low core recovery associated with sandy sediments.

     

    Log-Seismic Correlations

    Figure 11. Natural gamma ray, electrical resistivity, and sonic logs at Sites U1353, U1354, and U1351. Correlations between seismic sequence boundaries (U10-U13) and logs are highlighted in yellow intervals. In particular, U10 through U12 are distinct features in the logging data, characterized by low gamma radiation, high resistivity, and increased Vp and Vs, that can be correlated across the three shelf sites. Sonic logs from all three sites have been preliminarily reprocessed (Guerin, postcruise research). GR gamma radiation; IDPH deep induction resistivity log.

    Repeated trends in gamma ray, resistivity, and velocity logs in the upper ~300 meters below sea floor across the three shelf sites (landward to basinward, U1353, U1354, and U1351) strongly support the continuity of seismic stratigraphy across the continental shelf. Figure 11 shows a preliminary site-to-site correlation between logs and seismic sequence boundaries. These correlations are supported by good agreement between distinct seismic reflections (U10-U12) and synthetic seismograms at Sites U1353 and U1354 (Figures 9 and 10, respectively). Strong coherence patterns in velocity logs from shelf Site U1351 (Figure 6), which were not properly labeled by the shipboard algorithm, suggest that the corresponding sequence boundaries will also be apparent at Site U1351 when the sonic logs are reprocessed. Logs were recorded in younger sediments at slope Site U1352 and post-cruise analysis of synthetics may lead to correlations with younger seismic sequence boundaries (U14-U19).

References Cited

    Archie, G.E., 1942. The electrical resistivity log as an aid in determining some reservoir characteristics, J. Pet. Technol., 5, 1-8.

    Collett, T.S., 1998. Well log evaluation of gas hydrate saturations, Trans. SPWLA Annual  Logging Symp., 39, paper MM.

    Jarrard, R.D., Dadey, K.A., and Busch, W.H., 1989. Velocity and density of sediments of Eirik Ridge, Labrador Sea: control by porosity and mineralogy, Proc. ODP, Sci. Res., 105, College Station, TX (Ocean Drilling Program), 811-835.

    Schlumberger, 1989. Log Interpretation Principles/Applications: Houston (Schlumberger Educ. Services), SMP–7017.

    Shipboard Scientific Party, 1999. Site 1119: Drift Accretion on Canterbury Slope. In Carter, R.M., McCave, I.N., Richter, C., Carter, L., et al., Proc. ODP, Init. Repts., 181, College Station, TX (Ocean Drilling Program), 1-112.


    Angela Slagle: Logging Staff Scientist, Borehole Research Group Lamont-Doherty Earth Observatory of Columbia University, PO Box 1000, 61 Route 9W, Palisades, NY 10964, USA
    Email: Angela Slagle

    Saneatsu Saito: Logging Scientist, Institute for Frontier Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061 Japan
    email: Email: Saneatsu Saito

     


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