Core Logging Lab

Gamma Density A gamma ray source and detector are mounted across the core on a sensor stand that aligns them with the centre of the core. A narrow beam of collimated gamma rays is emitted from a 137-Caesium source with energies principally at 0.662 MeV. These photons pass through the core and are detected on the other side. At this energy level the primary mechanism for the attenuation of gamma rays is by Compton scattering. The incident photons are scattered by the electrons in the core with a partial energy loss. The attenuation, therefore, is directly related to the number of electrons in the gamma ray beam (core thickness and electron density). By measuring the number of transmitted gamma photons that pass through the core unattenuated the density of the core material can be determined.

P-wave velocity The centre frequency is 230 kHz, and the design achieves a Q-factor of lower than 3.5 as a result of the inherent material properties combined with careful attention to the mounting and matching. The sound beam is collimated by near field effects to core diameters of 100 mm. The high S/N (signal to noise) ratio resulting from the use of the lower frequency and good coupling, combined with the wide bandwidth, mean that precise repeatable and automatic timing measurements can be made, and they offer the option of further pulse processing in the frequency domain. Other frequency ranges can be made to order.

Magnetic Susceptibility An oscillator circuit in the sensor produces a low intensity of approximately 80 ampere per meter (A/m) root mean squared (RMS) non-saturating, alternating magnetic field (0.565 kHz for the MS2C sensor and 2 kHz for the MS2E sensor). Any material in the near vicinity of the sensor that has a magnetic susceptibility will cause a change in the oscillator frequency. The Geotek MSCL system electronics convert this pulsed frequency information into magnetic susceptibility values reported as SI or CGS.

Geoscan V linescan Imaging Single lines of image data are collected sequentially down the core. Line-scan images are far superior to area camera images because they do not suffer from uneven lighting, spherical distortion, montage or “stitching” effects. The entire image is suitable for calibrated sub-millimetre image analyses. Images can be collected over the full core width between 100 and 1000 lines per centimetre, corresponding to 100 and 10 micron pixel sizes, respectively. Images are output as 48-bit RGB TIFF images but are quickly and easily converted to JPEG or other formats as required. Each Geotek core section image has a companion XML metadata file, containing important metadata pertaining to the core section and imaging conditions. A ruler can be generated next to the image, depicting either depth in core section or depth in core.

Colour Spectrometry The CM-700d spectrophotometer uses a diffused illumination, 8 degree viewing angle with a pulsed xenon lamp providing the illumination. The instrument detector collects light in 10 nm increments between 400 nm and 700 nm wavelength ranges. The spectrophotometric method utilises multiple sensors to measure the spectral reflectance of the object at each wavelength or in each narrow wavelength range. The sensor’s electronics then calculate the tristimulus values from the spectral reflectance data using integration. The measuring aperture is selectable between 8 mm (MAV) and 3 mm (SAV). For each measurement, data for the specular components included (SCI) and excluded (SCE) are recorded simultaneously to analyse the core surface.

Equipment note: Core accepted: Length: up to 155 cm; Diameter: up to 11 cm. Core motion: Fully automated motion. Linear precision: 0.01 mm. Scan speed: Typical logging speed 4 m/hr Data output: Tab-delimited ASCII files containing all measured parameters vs. depth in section and core. Data collected from all sensors simultaneously, displaying co-registered data sets in real time.

Visually flat images can be created from scanned whole or split cores using software corrections. Data from the 14-bit digital flat panel is output to the user as 16-bit grayscale TIFF images with a typical resolution of 120 microns; these images can easily be converted to JPEG or other formats. Core can be rotated under manual or computer control to examine structures. X-ray source: 65W Voltage range: 45 to 130 kV X-ray spot size: 50 to 100µm Detector: 1920x1536 pixel Image resolution: 40 to 300µm Output: 16-bit TIFF Rotation accuracy: 0.002 degree

Equipment page URL: https://www.geotek.co.uk/x-ray-ct-system/geotek-xct/

Equipment note:

Detector: Standard X-ray CT System: A cabinet based lead-lined steel system fully enclosing an X-ray source, detector and samples to be imaged. The instrument will be specifically calibrated for different core samples and will collect images on split or whole cores on plastic or metal liners, up to 150cm long and 15cm diameter. X-ray data are acquired in accordance with ASTM D4452-14.

CORE ACCEPTED: Length: up to 150 cm. Diameter: up to 15 cm. CORE MOTION: Fully automated motion. Linear precision: 0.01 mm. Angular precision: 0.01 degrees. SCAN SPEED: Average linear scan time for standard resolution: 5 minutes / 150 cm.