Pressure Core Analysis
PCATS: Pressure Core Analysis and Transfer System
Pressure cores are taken in geological formations where the preservation of in situ pressures during recovery is important to maintain the physical, chemical or biological components of interest. The most common reason pressure cores have been recovered to date is for the preservation of gas hydrate and the sedimentary structures in which it forms.
Gas hydrate dissociates during or soon after core recovery as a result of decreasing pressure and increasing temperature. The dissociation of gas hydrate creates large volumes of gas that expand and can destroy the complete fabric of the core prior to it reaching the surface. Cores recovered at or near in situ pressures and temperature preserve the contents for analysis in the laboratory.
Pressure core handling and analysis under pressure
To complement coring systems that recover cores under in situ pressures, a core handling and analysis system is needed that can operate at the same high pressures.
Geotek specialises in providing such a system in the form of the PCATS, an integrated Pressure Core Analysis and Transfer System. The PCATS provides the mechanism and infrastructure whereby pressure cores can be transferred from the coring autoclave into a measurement chamber, non-destructively analysed providing simple geophysical data and X-ray images, sub-sampled, and transferred into customised pressure chambers for transport or further analysis. Controlled depressurization and degassing for on-board hydrate quantification is one of many potential further analyses.
Immediate core evaluation
As cores are withdrawn from a compatible pressure corer autoclave, they are X-rayed to determine the length, quality, and contents of the core.
These X-ray images allow the core to be immediately evaluated and the fate of the core decided: a) which parts of the core will be stored, and for what analyses; b) which parts will be rapidly de-pressurised for visual observations or storage in liquid nitrogen; and c) which parts will be slowly depressurised for gas hydrate quantification.
Rapid core assessment also permits identification of cores which have not recovered their targets and must be retaken.
The Pressure Multi-Sensor Core Logger (MSCL-P) is an integral component of the PCATS that enables automated, high-resolution, non-destructive measurements to be made on pressure cores at in situ conditions. Cores can be both translated and rotated under computer control past the MSCL-P sensors: gamma density, P-wave velocity, and X-ray CT.
Multiple data sets at varied orientations can be collected for each core, including movies of single locations being rotated in the X-ray beam. Full X-ray reconstructions of cores under pressure are currently in development.
These data, collected immediately onboard ship, provide the user with both quantitative information on the nature of the formation recovered as well as detailed qualitative information about the nature of sedimentary and other structures.
A new feature of the PCATS is its ability to section cores into shorter lengths while still at in situ pressures. Once all the non-destructive measurements have been completed in the MSCL-P, a core can be cut under pressure at multiple, client-defined locations along its length and the pieces transferred to customised storage or analysis chambers. This provides for much higher levels of flexibility than hitherto possible and greatly enhances the versatile nature of the device.
The main body of the Geotek PCATS is set up inside a portable 20-foot laboratory container for easy transportation to seagoing or shore-based operations. Once on site, portions of the PCATS extend from each end of the container.
Core processing speed
An average cycle of core extraction, non-destructive analysis (0.5 cm resolution, one data set), sub-sampling, transfer of core sections (4), and preparation of the PCATS to receive the next core can take approximately 2-5 hours, depending on core length. During intensive pressure coring operations, cores can be transferred to holding chambers for temporary storage at high pressure.
- Pressure rating: 350 bar maximum working pressure
- Temperature range: 4-20˚C working temperature
- Gamma density sensor: Lead-shielded 137Cs 10 mCi source and NaI detector
- P-wave velocity sensor: Geotek 250 kHz ultrasonic transducers
- X-ray CT imaging system: 130 kV microfocal X-ray source with digital image intensifier capture system
- Dimensions: 1m corers: 20-foot laboratory container with extensions; 3.5m corers: 3 x 20-foot laboratory containers
- Compatible coring systems: Aumann Associates HPTC & Hybrid PCS (3.5m), Fugro FPC (1m), Fugro FRPC (1m)
Download Geotek Pressure Core Analysis flyer in PDF format below