Current Offshore Coring Tools and Technologies: an Overview

1. Current Offshore Coring Tools and Technologies: an Overview CVE 582 – Seabed Geotechnics Professor: Dr. Moran Presented by: Michael Jander Date: 12/04/2008

2. Introduction • Purpose of sampling: • Collecting representative and undisturbed samples of sediment to be investigated • Many factors affect the selections of sampling tools • Two different coring systems: • Gravity (Wire-line) Systems • Drilling Systems

3. Gravity (Wire-line) Systems • Functional principle: • Weights mounted on sampler  Provides force to drive it into the seafloor • Advantages: • Relatively inexpensive • Easy operation • Disadvantage: • Only a few meters of sample can be recovered • Main gravity systems: • Box Corer • Gravity Corer • Piston Corer

4. http://www.kc-denmark.dk Box Corer • Functional principle: • Weights mounted on box corer provide force to penetrate seafloor • After box is filled with sediment, securing the sample by moving the spade-lever arm underneath the sample • Advantages: • Minimal disturbance to sediments • Simple to operate • Great sample volume • Disadvantages: • Only for fine-grained sediments • Only for sampling top layers of sediment • Heavy to transport/deploy

5. http://www.kc-denmark.dk Gravity Corer • Functional principle: • Free-fall to the seafloor and penetration through own weight • Watertight valve at the top of the core liner prevents washout of the sample • Steel core catcher at the bottom • PVC core tubes for retaining the sample • Advantages: • Easy to use • Requires little maintenance • Disadvantages: • Heavy to deploy and recover • Disturbed samples (‘raking’ of core catcher)

6. Piston Corer • Purpose of triggering mechanism: free-fall over known height • Functional principle: • Core barrel slides past a piston (remains stationary) • Piston creates partial vacuum  facilitates sample entry • Advantage: undisturbed sample • Disadvantages: • Large vessel required due to large weight • Requires experienced operators

7. Drilling Systems • Originally derived from oil industry • First adopted by the Deep Sea Drilling Program (DSDP) • Mainly a combination of Hydraulic Piston Coring and Rotary Drilling • Advantages: • Better quality for undisturbed samples • Samples from further below the seafloor • Disadvantages: • Need of a drill ship or platform

8. Figure: Schematic of drilling equipment on the JOIDES Resolution drill ship (ODP) Drill Vessel/Platform • Drill String consists of: • Drill Pipe • Bottom hole assembly • Drill bit • Bottom-Hole Assembly (BHA) • Includes the core bit, outer core barrel, various subs, and drill collars • Provides weight to the drill or core bit • Active and passive heave compensator systems permits drilling/coring with ship heave of up to 4.9 m

9. Rotary Core Barrel (RCB) • Used in medium to hard crystalline sediments • Functional principle: • RCB inner core barrel free falls through the drill string and latches into the BHA • BHA is rotated with the drill string while bearings allow the inner core barrel to remain stationary • Inner core barrel can hold a 9.5 m core and is retrieved by wireline

10. Advanced Piston Corer (APC) • Functional principle: • Inner core barrel is run to bottom on wireline • Pump pressure is then applied to the drill pipe  severs the shear pins  strokes the inner core barrel 9.5 m into sediment • Inner core barrel retrieved by wireline • Advantages: • Compatibility to XCB • Rapid recovery of core • Recovery oriented core • Disadvantages: • Not functional in granular formations (such as sand) or hard ground • Core barrel may stick in firm sediments

11. Advanced Piston Corer (APC)

12. Extended Core Barrel (XCB) • Typically used when the formation is: • Too stiff for piston coring • Too soft for efficient recovery with RCB • Advantages: • Compatibility to APC • No artificial layering • Cutting shoe trims core • Not usable for: • Very soft sediments • Granular formations • Fractured rock or rubble • Hard igneous formations

13. Further Coring Technologies • Pressure Core Sampler (PCS) • Used in sediments while maintaining in situ pressure • Advanced Diamond Core Barrel (ADCB) • Used for firm to well lithified sedimentary or igneous formations • Used when APC, XCB and RCB are ineffective • Navidrill Core Barrel (NCB) • Motor-driven core barrel • Designed to apply diamond-coring technology to APC and XCB coring operations in the same BHA.

14. Conclusion • Variety of tools available for • Obtaining undisturbed and representative samples • Different sediment formations • Recovering samples from diverse depths below seafloor • Different objectives

15. Questions ???