2949775342

the terminal part of a core barrel suitable for soft soils

Picture 3

The tool is lowered inside the drillstring (casing) and recovered by a cable or wire (therefore called “wire-line”) moved by a special hoist. The wire has a “fishing-tool” (called “overshot”) attached at its end. Such an overshot is designed in a way which allows the hooking/unhooking operation in an automatic way.

The wire linę drilling operations are essentially executed as follows (referred to as c.c.drilling):

*    The drill rig pushes and rotates the casing inside which the core barrel is placed (the shape and length of the core barrel depends on the type of soil). Normally, mud circulation inside the drillstring is used. The mud leaves the terminal part between the core barrel and the casing without interfering with the inside of the core barrel.

*When the drilling is completed, the rotary head of the drill rig is moved away laterally and the overshot is lowered down into the drillstring by the wire, driven by a “high-speed” hoist. The overshot hooks and the core barrel can be recovered.

*    The core is taken out of the core barrel, which is cleaned and prepared for the next operation,

*    The core barrel is lowered inside the drillstring again and one morę rod is added at the top of the drillstring, the rotary head is connected to the rods, mud is injected and the drilling starts again.

The advantages of the wire-line system, compared to the traditional method are: better ąuality of the cores, higher percentage of recovery, faster execution , less power reąuired from the drill rig and the possibility to easily change between different types of tools.

2.2 PEZOCONE CPTWD

For the experimental CPTWD system, a standard piezocone, having a memory data storage capability, has been used. (Ref. 1)

This type of cone, conforms with the following standard: "International Reference Test Procedurę for CPT/CPTU from ISSMGE Rev.3". The accuracy class is classl.

In its’ "standard" version it is a system which measures Q_c, F_s, U, (point resistance, local friction, porę pressure and inclination of the drillstring every 2 cm of penetration (versus time in case of use in “memory modę”, without cable)

During the sounding, two data files are produced: one in the internal microprocessor inside the CPTU cone, and the other in the data collector; Picture 4.

Picture 4

After recovering the cone, it is connected to the data collector and its CPTU data will be downloaded. Proper software in the data collector will allow for the synchronization between the memorized data as a function of time (inside the cone), and those as a function of depth (inside the data collector) . In this way, it is possible to obtain a normal data-file (Qc, Fs, U, incl.) versus depth.

In the special "CPTWD" version, Picture 5, an additional pressure sensor for the evaluation of the U in one morę point of the piezocone (Uj location according to the International Standards) and a rotation sensor have been added. The latter allowing one to determine whether the piezocone has been subject to rotation during the sounding, or not.

The reason to detect Ui was to determine whether or not the U is affected by the overpressure caused by the injection of mud.