Core Logging

Automated non-destructive testing
Any core collected for a science or engineering objective can benefit from detailed non-destructive analysis. The use of Multi Sensor Core Logger (MSCL) systems to rapidly obtain high-resolution, down-core data from sediment and rock cores has become a standard procedure over the past 20 years. Measurements are used by scientists and engineers both intrinsically, for their actual values (e.g., gamma density, P-wave velocity), or as proxies for changes in lithology or formation environment (e.g., magnetic susceptibility).

The Standard MSCL-S is the ideal equipment for obtaining these data on whole cores in an accurate, easy, reliable and efficient manner. Once the system is set up for the particular core size being used and calibrated, individual core sections are simply placed on one end of the track and removed from the other when completed. All the sensors systems work in parallel providing rapid real time data of up to 100 metres of core per day.

The MSCL-S can be supplied in a portable 20-foot laboratory with other analysis equipment for seagoing or shore-based operations. However, if logistics require it, the equipment suite can be installed in a laboratory space on board a vessel or inside a building.

Quality assurance for cores and sub-samples
When MSCL logging is carried out at sea, the high-resolution core log data sets for each core are generated within hours of core recovery. These data provide the client with a rapid QA assessment of the cores recovered, identifying cores not fit for purpose that might need to be retaken. Quality assurance of core is also important prior to sub-sampling cores. Sub-sampling of cores for a variety of tests is a routine but important operation. The collection and examination of non-destructive testing data prior to sub-sampling ensures representative sub-samples are taken every time.

Gamma density
Attenuation of a beam of gamma radiation is measured, providing high-resolution density profiles down the core with spatial resolutions typically of 1 cm. Calibration is normally achieved with machined aluminium samples mounted inside a water-filled liner. For most sediments this empirical calibration technique provides gamma density values that agree very well with bulk density measurements made gravimetrically. In saturated sediments, density changes as a function of sediment type (sands are usually more dense than clays) with the density also increasing with burial depth due to compaction and de-watering.

P-wave velocity
Travel time of a compressional wave pulse is measured across the diameter of the core, providing accurate profiles of P-wave velocity down the core at a spatial resolution of about 1 cm. Ultrasonic pulses are transmitted and received by a pair of rolling 230 kHz transducers that contact the dry core liner without the need for any acoustic coupling fluid (water or gel). The diameter of the core is simultaneously measured using laser callipers. Calibration is achieved using a length of liner filled with distilled water at a known temperature. P-wave velocity is primarily a function of density or porosity in unconsolidated sediments but increases rapidly in consolidated and/or lithified sediments and rocks.

Electrical resistivity
Electrical resistivity is measured in a non-contact mode using a matched pair of inductive coils that simultaneously measure the resistivity of both the core and free air. This differential measurement provides stable values of electrical resistivity over more than 2 orders of magnitude with a down-core spatial resolution of about 3-4 cm, depending on core diameter. Calibration is achieved using short lengths of core liner filled with saline water at different known salinities. Electrical resistivity is most sensitive to changes in pore water salinity, but also varies as a function of sediment porosity and permeability.

Magnetic susceptibility
Inductive measurements of magnetic susceptibility are made using Bartington MS2C loop sensors with an internal diameter close to the core size. This sensor provides down-core spatial resolutions of 3-4 cm, depending on the core diameter. Calibration is checked using using a factory-supplied sample of known magnetic susceptibility together with a correction that is applied to account for core and loop diameters. Magnetic susceptibility varies as a function of the mineral content, translating to changes in sedimentary provenance or diagenetic environment, and is often used to correlate nearby cores.

MSCL-S specifications

• Core accepted: Length: up to 155 cm; Diameter: up to 15 cm
• Gamma density: Lead-shielded ¹³⁷Cs 10 mCi source and NaI detector with a typical accuracy of ±0.01 g/cc
• P-wave velocity: Geotek 230 kHz acoustic rolling transducers and laser callipers. Typical accuracy ±5 m/s
• Electrical resistivity: Geotek non-contact inductive electrical resistivity sensor. Typical accuracy ±0.2 ohm•m
• Magnetic susceptibility: Bartington magnetic susceptibility MS2C loop sensor. Typical accuracy ±5%
• Core motion: Fully automated motion. Linear precision: 0.1 mm
• Data output: Tab-delimited ASCII files containing all measured parameters vs. depth in section and core: core diameter, gamma density, P-wave velocity, electrical resistivity, magnetic susceptibility, calculated porosity, and calculated acoustic impedance
• Scan speed: Typical logging speed 4 m/hr

  

  Download Geotek Core Logging Service flyer in PDF format below