Evaluation of Quality of Geochemical Log Data in ODP Hole 798B

Bristow, Jim; deMenocal, Peter B

doi:10.2973/odp.proc.sr.127128-2.221.1992

Cited by 7 publications

(3 citation statements)

References 8 publications

(14 reference statements)

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“…These break-outs occur over relatively small intervals (c. 2 m) and so only a small amount of logging data have been lost due to the stand-off effect. Individual tools are affected to different degrees by stand-off, but the ACT is particularly sensitive to this effect and as such can be used as a monitor of tool performance (Bristow & deMenocal 1992). In Hole 896A the A1 yields from the ACT rapidly fall in the break-outs, but in the remainder of the hole the small scale relief of the borehole does not significantly affect this tools performance (Fig.…”

Section: Logging Tools and Datamentioning

confidence: 99%

Ocean floor volcanism: constraints from the integration of core and downhole logging measurements

Brewer

Harvey

Lovell

et al. 1998

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The volcanic architecture of oceanic crust records the diversity in volcanic activity during its development in the neovolcanic zone of individual ridge systems. Potentially there exists a spectrum of lithological architectures which may primarily be related to the spreading rate and the dynamics of individual magma chambers along different ridges. Recent studies have emphasized the observable spatial variations within different neovolcanic zones, although direct extrapolation into the third dimension can only be achieved by the use of drilling results. To study the structure of the volcanic layer it is essential that individual lithologies (sheet flows, pillow lavas and/or breccias) can be discriminated from the core and/or logging results and mapped within the borehole. Unfortunately a problem with the drilling of the volcanic basement during the Ocean Drilling Program has been the generally low (typically c. 25%) and biased core recoveries, which produce an erroneous picture of the lithological diversity of the volcanics. This problem is further compounded by the difficulty in determining the volcanic stratigraphy, particularly when the key information is lost during coring (i.e. boundaries/contacts). Downhole logging provides near continuous records of the physical/chemical properties of the borehole which when integrated with core measurements, yield a detailed picture of the architecture of the volcanic layer. Logging results from ODP Hole 896A are of sufficient quality that sheet flows, pillow lavas and brecciated units can be discriminated and mapped effectively within the borehole. From their distribution it is evident that sheet flows become more abundant in the lower part of the hole, which probably correlates with ridge axis volcanism whereas, the predominance of pillow lava flows (< 340 mbsf (metres below sea floor)) in the upper part of the hole, is probably related to off-axis volcanism within the neovolcanic zone.

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Section: Logging Tools and Datamentioning

confidence: 99%

Ocean floor volcanism: constraints from the integration of core and downhole logging measurements

Brewer

Harvey

Lovell

et al. 1998

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“…In some environments logged by ODP certain elements are below the detection resolution of the tool (Bristow and deMenocal, 1992;Jarrard and Lyle, 1991). This is more often the case in high-porosity environments, where most of the detected gamma-ray spectrum is derived from Cl and H in the formation and borehole, rather than from the rock matrix.…”

Section: Reconstruction Of the Relative Elemental Yields From The Recmentioning

confidence: 96%

Data Report: Geochemical Logging Results from Vanuatu: Sites 829, 830, 831, and 833

Bristow¹,

Dove²,

Broglia³

et al. 1994

Proceedings of the Ocean Drilling Program

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Geochemical well logs were obtained in the igneous and sedimentary sequences drilled at Sites 829, 830, 831, and 833 of Ocean Drilling Program Leg 134. Corrections have been applied to the logs to account for variations in borehole size, borehole fluid composition, downhole temperature, and logging speed. Concentrations of the elements Th, U, and Gd, and the dry weight percentages of the oxides of Si, Ca, Al, Fe, Ti, and K have been derived. In each of the logged holes the log-derived geochemistry agrees well with shipboard carbonate-derived CaO and X-ray fluorescence core measurements.

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“…As an alternative to the gamma ray core measurement, Bristow & deMenocal (1992) use a 'proxy' terrugineous curve produced from core data to match to the logged gamma ray curve (SGR). This terrugineous curve is calculated as the residual opal content (100% minus opal wt% content).…”

Section: Incorrect Depth Assignmentmentioning

confidence: 99%

Aspects of core-log integration: an approach using high resolution images

Lofts¹,

Bristow

1998

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Core-log comparisons are often not considered routinely enough within the exploration environment. This may be for a number of reasons, such as problems with depth-matching the core and log datasets, the environment of acquisition of both datasets, the lack of understanding of log and core acquisition or a lack of confidence in laboratory or log measurements. These problems are discussed as a preliminary step to the development of a strategy aimed at improving core-log integration.Using recent technological advances in the side-by-side presentation of core and high resolution image data from logging tools, a strategy is presented with the aim of making core-log integration more rigid and routine. Features in both core and images are correlated interactively--thus ensuring the best possible integration. This is a two stage process involving core-to-image matching, and then image-to-log matching. This strategy has the potential to make core-log integration more accurate and as a result enable the interpreter to realize the most from sub-surface data.Borehole logging provides quasi-continuous (typically every 150mm), in situ measurements

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Evaluation of Quality of Geochemical Log Data in ODP Hole 798B

Cited by 7 publications

References 8 publications

Ocean floor volcanism: constraints from the integration of core and downhole logging measurements

Ocean floor volcanism: constraints from the integration of core and downhole logging measurements

Data Report: Geochemical Logging Results from Vanuatu: Sites 829, 830, 831, and 833

Aspects of core-log integration: an approach using high resolution images

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