A New Method for Quality Control of Geological Cores by X-Ray Computed Tomography: Application in IODP Expedition 370

Abstract

X-ray computed tomography (XCT) can be used to identify lithologies and deformation structures within geological core, with the potential for the identification processes to be applied automatically. However, because of drilling disturbance and other artifacts, the use of large XCT-datasets in automated processes requires methods of quality control that can be applied systematically. We propose a new systematic method for quality control of XCT data that applies numerical measures to CT slices, and from this obtains data reflective of core quality. Because the measures are numerical they can be applied quickly and consistently between different sections and cores. This quality control processing protocol produces downhole radiodensity profiles from mean CT-values that can be used for geological interpretation. The application of this quality control protocols was applied to XCT data from International Ocean Discovery Program (IODP) Expedition 370 Site C0023 located at the toe of the Nankai accretionary complex. The evaluation of core quality based on this protocol was found to be a good fit to standard-evaluations based on the visual description of core, and could be used to select samples free from drilling disturbance or contamination. The quality-controlled downhole mean CT-value profile has features that can be used to identify lithologies within a formation, the presence and type of deformation structures and to distinguish formations.

Temperature limits to deep subseafloor life in the Nankai Trough subduction zone

“…The morphology of the authigenic minerals in veins and burrows suggest that the ingression of such fluids started before and continued throughout the deformation of underthrust sediments (15). Tsang et al (15) estimate the duration of individual hydrothermal fluid flow events by fitting a heat flow model, which predicts the spatial and temporal expansion of thermal aureoles along permeable sedimentary fabrics, to the actual size of hydrothermal veins and alteration patches observed by visual core description and radiodensity logging (14,50). They conclude that the ingression of hydrothermal fluids has occurred in the form of episodic short-term pulses, which have lasted for less than three days and altered sediment temperatures within up to 30 cm thick aureols around veins or alteration patches (15).…”

“…X-ray CT-imaging not only allows one to identify and to avoid core intervals with fractures prone to contamination, it also enables quantification of core integrity and thus contamination risk for each selected sample (50). Using automated image and data processing routines, pristine, high-quality areas can be distinguished from damaged areas based on the characteristic values and distribution patterns of radiodensity in each 0.625 mm thick slice image recorded as a DICOM file during X-ray CT scanning.…”

“…The resulting slice quality (SQ) is a quantitative measure for the relative abundance of drilling induced fractures in a given slice, with a SQ of 100% indicating the highest possible quality of a slice without any fractures. SQ has been shown to be an effective quality control measure, and automatic identification and removal of slices below a given SQ threshold generates quality-controlled downhole radiodensity profiles closely reflecting geological features (50). A detailed description and evaluation of this new method and its application during Expedition 370 are given in ref.…”

Potential of Dual and Multi Energy XRT and CT Analyses on Iron Formations

“…The idea of X-ray computed tomography (CT) was first mentioned in a Soviet-Russian publication of Korenblum et al in 1958 [ 7 ] but found lesser attention due to the language barrier than the well-known publication of Hounsfield in 1973 [ 8 ]. In both early cases, the method was developed for the use in medical imaging but today CT is also applied in other fields like earth sciences, and exploration and mining [ 9 , 10 , 11 ]. It is a non-destructive technique that allows three-dimensional (3D) visualization of internal structures of rock samples.…”

X-ray Computed Tomography as a Tool for Screening Sediment Cores: An Application to the Lagoons of the Po River Delta (Italy)

“…This analytical technique allows the non-destructive examination of bulk density, porosity, multiplanar visualisation of structures and 3D images of larger objects, burrows and gas bubbles, and it appears as a valuable tool for controlling core quality and identifying lithology (e.g. [2][3][4][5][6][7][8]).…”