2949775341

CPTWD (Cone Penetration Test While Drilling) a new method for deep geotechnical surveys

Authors :    Massimo Sacchetto-Engineer-: S P G drilling company -Adria (Ro) Italy

Kjell Elmgren - Engineer - ENVI Environmental mechanics - Alingsas Sweden Annalisa Trevisan - Engineer - S P G drilling company -Adria (Ro) Italy Kenth Melander - Engineer - ENVI Environmental mechanics - Alingsas Sweden

ABSTRACT: CPTWD represents integration of: wire-line drilling system, standard and modified piezocone, MDW-monitoring while drilling. During the CPTWD test the cone is protruding in front of the drill bit during drilling in the same way as a corer; CPTU data are stored in memory unit. At the same time as the CPTU data are logged, drilling parameters (MWD) are also recorded. The system allows for the change between CPT testing, continuous core drilling, down-hole testing and non coring drilling with MWD. The combination of CPT parameters and drilling parameters can be a very powerful basis for interpretation of the data. The advantages of this system compared to the other down hole type CPTU is that much longer strokes than the normal 3 m can be madę. In addition, the information from the drilling parameters is very useful, especially in hard formations where CPTU cannot be performed. It is expected that futurę development work will improve the method in terms of the test procedures and in terms of capabilities of the system itself, by adding new tools (e.g. field vane test, Permeameter, fluid sampler, thin wali samplers, dilatometric DMT).

Picture 1

The drill mud will flow in the annular space between the external wali of the core barrel and the internal wali of the rods and “lubricates” the walls of the hole while removing the cuttings.

Most of the time the mud is recycled and stored on the surface before it is put back into circulation.

The following Picture 2 shows a typical installation for a wire-line c.c.drilling:

1    INTRODUCTION

The CPTWD is the acronymous of Cone Penetration Test While Drilling. Basically it can be considered as an integration between a wire-line system (core barrel, non coring device, cable recovery system, etc), piezocone and the MWD (Monitoring While Drilling) system.

Prior to the introduction of the CPTWD, it is necessary to briefly outline every part of the system : the wire-line system, the piezocone, the MWD.

2    DESCRIPTION OF THE SYSTEM

Picture 2

There are different types of core barrels as well as different types of tools which can be placed inside the drillstring (rods). The following Picture 3 shows

2.1 WIRE-LINE SYSTEM The “recovery by cable or wire” system (hence the name “wire-line”) is based on the use of a core barrel which, integrated with the casing, makes a unique body. Pushing and rotation are conveyed by the same casing.

The system is essentially composed of:

♦Drilling rods (or "casing") inside which, at the bottom terminal part, there is an element (usually a slot) where the core barrel is lowered down by the wire and takes place inside, so allowing the drilling rods to rotate and push.

*Core barrel or drilling tool: this is placed inside (throughout the interior of) the drilling rods and has a hook up system. In the following Picture 1, the particulars of a four hooks system are shown: