D M T 2006D M T 2006

Electronic DMT for great depth

Drilling and coring

For shallow continuous coring bore-holes the commoniest method is using the “simple tube core barrel”As the name says it is a simple tube (commonly its length varying from 1,5 to 3 m) which is pushed into the soil by the drill rig. Depending on the type (loose, soft, cohesive, etc) of soil (i.e. clay, sand, gravel) the core barrel is simply pushed, pushed and rotated, sometimes hammered or also pushed by vibrating it. If the soil collapses (almost always) the hole is cased with the casing drillstrings.Therefore the commoniest method to perform continuous coring bore holes is an alternance of coring with the core barrel and casing the previously cored length of the hole, as shown in the following picture:

Coring and casing-sketch-C= coring

R= casing

THE CORE BARREL IS ALWAYS DRIVEN BY RODS WHICH ARE SCREWED AND UNSCREWED EVERYTIME

Advantages and disadvantages of using rods and casing

Advantages:• Simplicity of use • “idiot-proof” operations• low cost of the drilling tools•No special requirements for water/mud pumps•Fast installation of the drill rig

DISADVANTAGES:•Poor quality of the cores (the friction with the inside walls of the core barrel sometimes causes burning and cementation of the core)•Very often : poor recovery (expecially in loose soils)•Very slow operations by increasing the depth: the more is the depth the more rods have to be screwed (to lower down the core barrel) and unscrewed (to retrieve the core barrel)•Much more “hand-power” required (for screwing/unscrewing the rods hundreds times per day)•Much more power required to the drill rig, expecially for the casing

WIRE-LINE

• 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 sole body. Pushing and rotation are conveyed by the same casing.

• The system is essentially made up 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.

WIRE-LINEThe drill mud will flow into the annular space between the external wall of the core barrel and the internal wall of the rods and “lubricate” 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. There are different types of core barrels as well as different types of tools which can be placed inside the drill string (rods) The tool is lowered inside the drill string (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.

Mud pools in WL installation

Hooking systemAndOvershot

WIRE-LINE

The wire-line drilling operations are essentially executed as follows (referred to as c.c.drilling): 1 The drill rig pushes and rotates the casing inside which the core barrel i s placed (the shape and

length of the core barrel depends on the type of soil ). Normally , mud circulation inside the dril l string is used. The mud leaves the terminal part between the core barrel and the casing without interfering with the inside of the core barrel.

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

3 The core is taken out of the core barrel, which is cleaned and prepared for the next operation. • Th e core barrel is lowered insid eth e drill strin gagain an don emore rod is adde d at th eto p

of the dr ill strin ,g the rotar y head is connected to the ro ,ds m udis injected and the drilling starts again.

NOT A SINGLE ROD IS SCREWED/UNSCREWED FOR LOWERING AND RECOVERING THE CORE-BARREL

ONLY THE “CASING” RODS ARE SCREWED ONCE FOR DRILLING AND UNSCREWED ONCE FOR RETRIEVING

NO HAND-POWER REQUIRED -IT IS COMPLIANT TO ALL SAFETY REQUIREMENTS-

WIRE-LINE detailsCasing = drill rods

Internal core-barrel OR no-coring assemply ORSampler OR special tool (medusa, CPT, etc)The INTERNAL CORE-BARREL can be rotatingOr not rotating (having bearings under theHooking system preventing from rotation)

HOOKING SYSTEM

Water/mudflowing

WIRE-LINE drill rig

BASICALLY THE DRILL RIG APPLIES“ENERGY” TO THE CASING RODSIN FORM OF TORQUE (for rotation)THRUST (for pushing and pulling) ANDWATER/MUD PRESSURE (for “cutting” theSoil and lift the cuttings up)

Lowering CB

Lowering CB

HOOKING(the corebarrelLatches insideThe rods)

hooking

ROTATION

PUSHING

WATER/MUD INJECTION

CORING

END OF CORING

OVERSHOT

INSERTING THE

OVERSHOT

wire

LOWERING THE

OVERSHOT

UNLATCHING THE

COREBARREL

Lifting the CB up

Lifting the CB up

Lifting the CB up

Recovering the cb

ADVANTAGES OF WIRE-LINE

The advantages of the wire-line system, compared to the traditional method are: better quality of core, higher percentage of recovery, faster execution , less power required from the drill rig and the possibility to easily change between different types of tools. Therefore it is considered to be the best method to carry out deep geotechnical surveys and offshore/nearshore surveys

C P T W D:CONEPENETRATIONTESTWHILEDRILLING(uses wire-line)

NEARSHORE/OFFSHOREGEOTECHNICAL SURVEYS

ADVANTAGES OF WIRE-LINE•Quality•speed of execution almost independent from depth•Flexibility (wide choice of tools can be used: corebarrels, special tools, no-coring assembly, etc)•The hole is ALWAYS cased•Much less “horsepowers” are required to the drill rig (the casing is always rotating, no great friction outside the casing rods)•SAFETY•No “hand-power” is required, the Operators are not so much stressed•Can be used in ALL type of soils (it was born for rock coring)

DISADVANTAGES OF WIRE-LINE

•It is much more complicated than the “simple core + rods” method• it must be used ONLY by very-skilled (and smart) Operators•The installation of the drill rig is very slow, more or less same time is required for a 15 m or 150 m deep bore-hole!•The drilling tools are much more expensive, so as the mud-pumps, pools, etc• it is not raccomandable for shallow “environmental” surveys, because there is water/mud circulation (it might cause cross contamination)

MEDUSANothing to deal with jellyfish, but the way of moving looks like it

Basically is a standard dilatometer (in terms of sizes and principle of functioning); differently from the standard equipment it is managed electronically and the bottle of nitrogen is contained inside a special wire-line “core-barrel”.No tools are placed in the surface, no manometers, no bottle; just a laptop, in order to download data and show on the screen the operationsIt is used inside a standard wire-line, whose outer diameter is 130 mm.Same wire-line can be used for continuous coring, sampling, no coring (with or without MWD), CPTWD.

DMT blade

50 mm diameterrods

“core barrel” andHooking systemNitrogen bottle

electronicsGENERAL VIEWOF MEDUSA(underground)

(above the ground)

General view of the system

Wire-line Casing rods

DMT

Photo # 1

Photo # 2InternalCorebarrel

ProtrudingRods andDMT

• The Medusa equipment functions as follow:• Inside the wireline casing rods is lowered the “core-barrel”

containing the bottle of nitrogen, the electronics, and having the DMT protruding 1,6-3,2 m (the lenght depending on some factors, such as (but not only): soil stiffness, thrust power of the drill rig, swelling or collapsing of the bottom of the hole, etc); prior of lowering it there is a synchronisation between the laptop and the electronics of Medusa. It is programmed the test (DEPTH, TIMES, ect)

• Once lowered the medusa core-barrel latches into the casing rods

• The operator knows that he must push the rods according to certain steps (pre-programmed rate of penetration) and stop the medusa every 20 cm of penetration; IN THE LAPTOP IS SHOWN EXACTLY HOW THE MEDUSA IS MOVING ACCORDING TO THE TEST AS PROGRAMMED

•The electronics manages the bottle with a valve in such a way to enflate and deflate the membrane (exactly as the standard DMT)•A pressure sensor detects the A and B values•The values (time, A, B) are memorised into the internal RAM•During the testing the laptop shows to the Operator how the medusa is moving

Once the corebarrel is lowered and the “brain” is connected again to the laptopThe software dowloads the A, B values

Electronics, synchronisation

BASIC OPERATIONSPrior to any pushing it has to be done the SETTING of the Medusa:•refilling/controlling the pressure of the nitrogen bottle•Control the DMT and the membrane• connecting the electronics to the laptop •PROGRAM THE TEST

Electronics(microcomputerInside theCorebarrel)

valve

LAPTOP

Making: A

Time to Push:01:30

SCREEN OF THE LAPTOPDURING THE TESTING

Drilling to depth -100 m by using one of the following methods:-no coring drilling (with or without MWD)-continuous core-CPTWD-sampling or testing

-100

Step 1

Lifting the rods up to -98,50 mAnd recovering the drilling tool.The hole is always filled with water+bentonite and/or polymers

-98,40

Water+bentonite filling

Step 2

-98,40

-100,00

Inserting the Medusa Core Barrel and latching itInto the rodsPrior to the inserting the microcomputer inside the corebarrel isResetted and the synchronisation with depth is done

N.B. the lenght of the rods protrudingOut the bottom of the drilling rodsShould be a multiple of 20 cm, normally varyingFrom 80 to 320 cm, in this case is 160 cm

Step 3

Pushing the medusa into the soil, with 20 cm steps.After each interval (20 cm) the pushing is stopped for a certainTime interval, allowing the DMT test to be done

-100,20……-101,60

Step 4

END OF PUSHING

-100

Step 5 a

END OF PUSHINGAnd recovering the medusa Core Barrel

Remoulded soil

Step 5 B

INSERTING A CONTINUOUS CORE BARRELAND CORING THE REMOULDED SOIL FOR CALIBRATION WITH THE DMT RESULTS

Remoulded soil

Step 6

NEW WAY OF DMT TESTING

• WL MEDUSA WILL ALLOW TO ACHIEVE DMT DATA AT A GREATER DEPTH with no need to drill with rods (therefore in much less time)

• THE INTERPRETATION OF THE DATA IS AS PER THE STANDARD

• The tested ground can be cored so to have a “qualitative” evaluation

• The results are again “not sensitive” to the method of pushing

POSSIBILE FIELDS OF APPLICATIONOF MEDUSA TECHNOLOGY

•Offhore drilling: the possibility to obtain DMT data without using a static penetrometer on a barge together with the drill rig allows less costs and more reliable data at the same time.•Testing in sites where the penetrometer is not usable (i.e. shallow gravel and then clay or silt/sand)•Testing inside a bore-hole instead of using other unreliable and sometimes expensive kind of test

The WL Medusa has been projected by:Prof.Silvano MarchettiMr.Diego Marchetti -Engineer-

Mr.Massimo Sacchetto Engineer-

THANK YOU