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THE CPTWD METHOD

Besides this, the rangę of U has also been increased to 50 Bar in order to achieve test depths down to 300 m.

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2.3 MWD (Monitor While Drilling)

It is a commonly and widely used method employed mainly in the deep oil drillings. It has been defined in several different ways, according to the company who built it, but is intemationally known as MWD (Monitor While Drilling).

In order to monitor the reaction to the penetration of the soil in the drillrig, pressure sensors in the hydraulic oil circuitry, depth transducers, volume transducers, etc are applied. In the specific case of the CPTWD, the sensors signals are conditioned and amplified in the data collector, where they are stored and printed out in real time while drilling.

The measured parameters could be all the ones during the drilling. Still, they normally are:

Bit-load (thrust pressure)

Torque ( rotation pressure)

-    Mud pressure

RPM (number of revolutions per minutę )

-    ROP ( ratę of penetration)

Mud flow (volume of injected mud / min.)

2.4

Basically, the CPTWD (CONE PENETRATION TEST WHILE DRILLING) system is an integration of the techniąues described above. A wire-line core barrel has been modified, allowing it to keep a CPTU cone inside in the centre in such a way, that the cone is protruding from the bottom of the drill- bit by at least 35 cm.

A MWD data recording system is connected to the drill rig. In this case it is practical if the data collector is capable of handling both the drilling parameters and the CPTU data at the same time. Practically, the performance of such system are the following:

•    Continuous core drilling, using the common core barrels, samplers, etc, but with the possibility of monitoring even the c.c.drilling with MWD; That is, to have a registration of all the implemented parameters even while carrying out a wire-line c.c.drilling.

•    MWD with non coring drilling: A non coring tool, for example a tricone (always wire-line) is fixed inside the drillstring so that during the drilling the data collector records all the relevant drilling parameters every 2 cm. In this way, it is possible to (together with the monitoring of the cuttings) establish the stratigraphy.

•    CPTU+MWD test at the same time: The CPTU cone-core-barrel is placed inside the drillstring. While the drillstring moves forward (at a speed as close as possible to the standard, 2 cm/s) the MWD system is always in function. After a substantial penetration, the CPTU cone is recovered, the data is downloaded to the data collector and subsequently synchronized with the corresponding MWD data. As a result, at the end of the drilling, it is possible to obtain a data matrix which includes (for every 2 cm of depth) for example: Qc, Fs, U₂, U3, Bit load, Torque, Mud pressure, ROP, Mud volume and RPM. During an interruption of the sounding it is possible at any time in order to carry out dissipation tests. The evaluation of the drilling parameters in real time can be useful to the operator who eventually decides when to interrupt the penetration of the piezocone (i.e. because the soil is too dense). (Ref 3).

•    It is useful to use the formula of the specific energy. This gives the Energy needed to penetrate one cubic meter of the soil materiał. (Ref. 2) For this reason (MWD), the CPTWD should not be